NCT7491_16 [ONSEMI]
Remote Thermal Monitor and Fan Controller;
| 型号： | NCT7491_16 |
| 厂家： | 
ONSEMI |
| 描述： | Remote Thermal Monitor and Fan Controller |
| 文件： | 总80页 (文件大小：791K) |
| 中文： | 中文翻译 | 下载： | 下载PDF数据表文档文件 |
NCT7491
Remote Thermal Monitor
and Fan Controller with
PECI 3.0 Interface and
SMBus Compatible Master
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The NCT7491 is a two−wire serially programmable hardware
monitor. It can monitor 2 remote temperature zones and its own
ambient temperature. A PECI 3.0 single wire interface allows the
NCT7491 to monitor CPU temperatures. The NCT7491 also
implements an SMBus compatible master, allowing it to read
automatically from thermal sensors on the SMBus. The NCT7491 can
automatically control the speed of 3 fans using PWM control, and
monitor the speed of 4 fans. There are 4 analog inputs, used for
measuring 12 V, 5 V, 2.5 V and Vccp channels. The NCT7491 supply
QFN24
MN SUFFIX
CASE 485L
QSOP24
RQ SUFFIX
CASE 492B
voltage and PECI V
voltage are also monitored. Each of the
TT
measured temperature, voltage and fan speed values are compared
with programmable limits and if any channel is outside the
programmed limit an interrupt is generated via the ALERT output pin.
A THERM output is also available for fail−safe thermal control. Up to
3 GPIO pins are available for digital control or signalling.
MARKING DIAGRAMS
NCT
7491
ALYWG
G
Communication with the NCT7491 is accomplished via the
(Top View)
2
SMBus/I C interface which is compatible with industry standard
protocols. The SMBus address is set by 2 address selection pins.
The NCT7491 is available in a 24−lead QFN or QSOP package and
operates over a supply range of 3.0 V to 3.6 V.
A
L
Y
W
G
= Assembly Location
= Wafer Lot
= Year
= Work Week
= Pb−Free Package
Features
(Note: Microdot may be in either location)
• PECI 3.0 Master for CPU Monitoring
• SMBus Compatible Master
• On−chip Temperature Sensor
NCT7491
YYWWG
A
• 2 Remote Sensor Channels
• Series Resistance Cancellation on Remote Sensors
• 3 PWM Fan Control Outputs
• 4 Tach Monitoring Input
(Top View)
(Bottom View)
NCT7491 = Specific Device Code
A
YY
WW
G
= Assembly Location
= Year
= Work Week
• PWM Automatic Fan Speed Control
• 4 Analog Inputs for Voltage Monitoring
• Vdd Supply Voltage Monitoring
= Pb−Free Package
• PECI V Voltage Monitoring
TT
• Overtemperature Outputs
ORDERING INFORMATION
See detailed ordering and shipping information in the package
dimensions section on page 79 of this data sheet.
• Limit Comparison of Monitored Channels
• SMBus Address Selection Allows up to 3 Devices
• Meets SMBus 2.0 Electrical Specifications (fully SMBus 1.1
compliant)
• These Devices are Pb−Free, Halogen Free/BFR Free and are RoHS
Compliant
© Semiconductor Components Industries, LLC, 2016
1
Publication Order Number:
June, 2016 − Rev. 3
NCT7491/D
NCT7491
Table of Contents
Features . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1
NCT7491 QSOP Pinout . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3
NCT7491 QFN Pinout . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3
Absolute Maximum Ratings . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4
Specifications . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4
QSOP & QFN Package Pin Assignments . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7
Comparison of NCT7491 and ADT7490 QSOP pinouts . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8
Functional Comparison between the NCT7491 and the ADT7490 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8
Functional Block Diagram . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9
Typical System Connections . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10
SMBus Slave Interface . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11
Analog Temperature Measurement . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13
Push Registers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15
PECI 3.0 Interface . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15
SMBus Compatible Master Port . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19
Automatic Fan Control . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22
Fan Override Settings . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26
Fan Drive . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26
THERM Assertion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 32
THERM Timer . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 33
SMBALERT Functions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 34
Voltage Monitoring . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 35
GPIO Functions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 36
VCCP Low Detection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 37
XNOR Tree Test Mode . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 37
Register Tables . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 38
Ordering Guide . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 79
QSOP Package Dimensions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 79
QFN Package Dimensions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 80
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NCT7491
NCT7491 QSOP Pinout
24
23
22
21
20
PWM1/XTO
1
2
3
4
5
6
7
8
9
SDA_S
SCL_S
GND
Vccp
+2.5Vin/THERM
VDD
SDA_M/GPIO1
SCL_M/GPIO2
PECI
+12Vin
+5Vin
NCT7491
TOP VIEW
(Not to scale)
19 GPIO3/THERM/SMBALERT
18
17
16
15
14
13
D1+
D1−
VTT
TACH3
D2+
D2−
PWM2/SMBALERT 10
TACH4/THERM/SMBALERT/
ADDR SELECT
TACH1
TACH2
11
12
PWM3/ADDREN
NCT7491 QFN Pinout
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NCT7491
Table 1. ABSOLUTE MAXIMUM RATINGS
Parameter
Rating
3.6 V
Positive Supply Voltage (V
)
CC
Maximum Voltage on +12V Pin
14 V
IN
Maximum Voltage on +5V Pin
6.25 V
IN
Maximum Voltage on All Open−Drain Outputs (excluding PWM pins)
Maximum Voltage on PWM Pins
3.6 V
+5.5 V
Maximum Voltage on TACH Pins
+5.5 V
Voltage on Remaining Input or Output Pins
Input Current at Any Pin
−0.3 V to +4.2 V
5 mA
Package Input Current
20 mA
Maximum Junction Temperature (T
Storage Temperature Range
Lead Temperature, Soldering
IR Reflow Peak Temperature
Pb−Free Peak Temperature
)
150°C
J max
−65°C to +150°C
220°C
260°C
300°C
Lead Temperature (Soldering, 10 sec)
ESD Rating
HBM
2 kV
FICDM
0.5 kV
Stresses exceeding those listed in the Maximum Ratings table may damage the device. If any of these limits are exceeded, device functionality
should not be assumed, damage may occur and reliability may be affected.
Specifications
T
A
= T
to T
, V = V
to V
, unless
operating down to V
. Timing specifications are tested at
MIN
MAX
CC
MIN
MAX
MIN
otherwise noted. All voltages are measured with respect to
GND, unless otherwise specified. Typical voltages are at T
logic levels of V = 0.8 V for a falling edge, and V = 2.0 V
for a rising edge. SMBus timing specifications are
guaranteed by design and are not production tested.
IL IH
A
= 25°C and represent a parametric norm. Logic inputs accept
input high voltages up to V , even when the device is
MAX
Table 2. SPECIFICATIONS
Parameter
Min
Typ
Max
Unit
Test Conditions/Comments
POWER SUPPLY
Supply Voltage
3.0
3.3
1.5
3.6
5
V
Supply Current, I
mA
Interface inactive, ADC active
CC
TEMP−TO−DIGITAL CONVERTER
Local Sensor Accuracy
0.5
0.25
0.5
3.5
3.5
°C
°C
°C
0°C ≤ T ≤ 85°C
A
Local Sensor Resolution
Remote Diode Sensor Accuracy
0°C ≤ T ≤ 85°C
A
−40°C ≤ T ≤ 125°C
D
Remote Sensor Resolution
0.25
30
°C
mA
mA
mA
mA
W
Remote Sensor Source Current
Low Level 1
High Level 1
Low Level 2
High Level 2
240
37.5
300
Series Resistance Cancellation
270
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NCT7491
Table 2. SPECIFICATIONS
Parameter
Min
Typ
Max
Unit
Test Conditions/Comments
ANALOG−TO−DIGITAL CONVERTER (INCLUDING MUX AND ATTENTUATORS)
Total Unadjusted Error (TUE)
2
1.5
1
%
%
For 12 V channel
For all other channels
8 bits
Differential Nonlinearity (DNL)
Power Supply Sensitivity
LSB
%/V
ms
0.1
11
Conversion Time (Voltage Input)
Averaging enabled, 16 samples per
averaged reading.
Conversion Time (Local Temperature)
Conversion Time (Remote Temperature)
Input Resistance
38
38
ms
ms
Averaging enabled, 16 samples per
averaged reading.
Averaging enabled, 16 samples per
averaged reading.
224
110
kW
kW
For +12 V channel
For all other channels
FAN RPM−TO−DIGITAL CONVERTER
Accuracy
10
14
%
%
0°C ≤ T ≤ 85°C
A
−40°C ≤ T ≤ 125°C
A
Full−Scale Count
65,535
Nominal Input RPM
109
329
RPM
RPM
RPM
RPM
Fan count = 0xBFFF
Fan count = 0x3FFF
Fan count = 0x0438
Fan count = 0x021C
5,000
10,000
OPEN−DRAIN DIGITAL OUTPUTS, PWM1 TO PWM3, XTO
Current Sink, I
8.0
0.4
20
mA
V
OL
Output Low Voltage, V
I = −8.0 mA
OUT
OL
High Level Output Current, I
0.1
mA
V = V
OUT CC
OH
OPEN−DRAIN SERIAL DATA BUS OUTPUTS (SDA, SDA_M, SCL_M)
Output Low Voltage, V
0.4
1.0
V
I
= −4.0 mA
OUT
OL
High Level Output Current, I
0.1
mA
V = V
OUT CC
OH
SMBus DIGITAL INPUTS (SCL, SDA, SDA_M)
Input High Voltage, V
2.0
V
V
IH
Input Low Voltage, V
Hysteresis
0.4
IL
500
mV
DIGITAL I/O (PECI PIN)
Supply Voltage
V
TT
0.85
1.26
V
V
Input High Voltage, V
0.55*V
IH
tt
Input Low Voltage, V
Hysteresis
0.5*V
V
IL
tt
0.1V
−6
V
Hysteresis between input switching levels
Output High Voltage, V = 0.75*V
tt
High level output source current, I
mA
mA
SOURCE
OH
tt
Low level output sink current, I
Signal noise immunity, V
0.5
1.0
Output Low Voltage, V = 0.25*V
SINK
OL
tt
300
mV
Noise glitches from 10 − 100MHz
Width up to 50ns
noise
p−p
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NCT7491
Table 2. SPECIFICATIONS
Parameter
Min
Typ
Max
Unit
Test Conditions/Comments
DIGITAL INPUT LOGIC LEVELS (TACH INPUTS)
Input High Voltage, V
2.0
V
V
V
V
IH
5.5
0.8
Maximum input voltage
Minimum input voltage
Input Low Voltage, V
IL
−0.3
Hysteresis
0.5
V
p−p
DIGITAL INPUT LOGIC LEVELS (THERM)
Input High Voltage, V
0.75 x
V
V
IH
V
TT
Input Low Voltage, V
0.4
IL
DIGITAL INPUT CURRENT
Input High Current, I
1
1
mA
mA
pF
V
= V
IH
IN CC
Input Low Current, I
V
= 0
IL
IN
Input Capacitance, C
5
IN
SLAVE SERIAL BUS TIMING (See Figure 1)
Clock Frequency, f
10
100
50
kHz
ns
ms
SCLK
Glitch Immunity, t
SW
Bus Free Time, t
SCL Low Time, t
4.7
4.7
4.0
BUF
ms
LOW
SCL High Time, t
50
ms
HIGH
SCL, SDA Rise Time, t
1,000
300
ns
ns
ns
ms
r
SCL, SDA Fall Time, t
f
Data Setup Time, t
250
15
SU;DAT
Detect Clock Low Timeout, t
35
Can be optionally disabled
TIMEOUT
MASTER SERIAL BUS TIMING
Clock Frequency, f
100
kHz
SCLK
t
R
t
F
t
LOW
t
HD; STA
SCL
SDA
t
t
SU; STO
SU; STA
t
t
t
HIGH
t
SU; DAT
HD; STA
HD; DAT
t
P
BUF
S
P
S
Figure 1. SMBus Timing Diagram for Slave Port and Master Port
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NCT7491
Table 3. QSOP & QFN PACKAGE PIN ASSIGNMENTS
QSOP
QFN
Pin No.
Pin No.
Pin Name
Description
2
1
22
SDA_S
SMBus/I C Slave Serial Bi−directional Data Input/Output. Open−drain pin; Re-
quires a pull−up resistor.
2
3
4
5
23
24
1
SCL_S
GND
Serial Clock Slave Input. Open−drain pin; Requires a pull−up resistor.
Ground
VDD
Positive Supply Voltage
2
SDA_M / GPIO1
Open−drain pin; Requires a pull−up resistor.
GPIO1 = General purpose I/O pin
2
SDA_M = SMBus/I C Master Serial Bi−directional Data Input/Output.
6
3
SCL_M / GPIO2
Open−drain pin; Requires a pull−up resistor.
GPIO2 = General purpose I/O pin
SCL_M = Serial Clock Master Output.
7
8
4
5
PECI
VTT
PECI input to report CPU Thermal Information. PECI voltage level is referenced
to the VTT input.
Voltage reference for PECI. This is the supply voltage for the PECI interface and
must be present to communicate over the PECI interface.
9
6
7
TACH3
Fan tachometer input to measure Fan3
10
PWM2 / #SMBALERT
PWM output to control Fan2. Can be configured as an SMBALERT output.
Open−drain pin; Requires a pull−up resistor.
11
12
13
8
9
TACH1
TACH2
Fan tachometer input to measure Fan1
Fan tachometer input to measure Fan2
10
PWM3 /
PWM output to control Fan3. If pulled low on power−up the NCT7491 enters
Address Select mode and the ADDRESS SELECT pin determines the slave
address. Open−drain pin; Requires a pull−up resistor.
#ADDREN
14
11
TACH4/
#THERM/
Fan Tachometer Input to Measure Speed of Fan 4. May be reconfigured as a
bidirectional THERM. Can be connected to thePROCHOT output of a processor,
to time and monitor PROCHOT assertions. Can be used as an output to signal
an overtemperature condition. The SMBALERT pin is used to signal out−of−limit
comparisons of temperature, voltage, and fan speed. This is compatible with
SMBus alert. Can also be used at device powerup to assign the SMBus ad-
dress. If THERM or SMBALERT is enabled then a pull−up resistor is required.
#SMBALERT/
#ADDRESS SELECT
15
16
17
18
19
12
13
14
15
16
D2−
D2+
D1−
D1+
Negative Connection for Remote Temperature Sensor 2.
Positive Connection for Remote Temperature Sensor 2.
Negative Connection for Remote Temperature Sensor 1.
Positive Connection for Remote Temperature Sensor 1.
GPIO3/
#THERM/
General−Purpose Open−Drain Digital Input/Output. Requires a pull−up resistor.
Can be configured as a bidirectional THERM pin or as an SMBALERT pin.
#SMBALERT
20
21
22
17
18
19
+5Vin
+12Vin
Analog Input. 0 V to 5 V.
Analog Input. 0 V to 12 V.
+2.5V / #THERM
Analog Input. 0 V to 2.5 V. May be reconfigured as a bidirectional THERM pin.
Can be connected to the PROCHOT output of a processor, to time and monitor
PROCHOT assertions. Can be used as an output to signal an overtemperature
condition. In THERM mode it is an open−drain bidirectional pin and requires a
pull up resistor.
23
24
20
21
Vccp
Analog input. Monitors CPU core voltage (to maximum 0f 3.0 V). This pin must
be connected to the NCT7491 supply voltage if it is unused.
PWM1 / XTO
PWM output to control Fan 1. Open−drain pin; Requires a pull−up resistor. Also
functions as the output for the XNOR tree test enable mode.
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NCT7491
Table 4. COMPARISON OF NCT7491 AND ADT7490 QSOP PINOUTS
QSOP Pin No.
NCT7491
SDA_S
ADT7490
SDA
1
2
SCL_S
SCL
3
GND
GND
4
VDD
VDD
5
SDA_M / GPIO1
SCL_M / GPIO2
PECI
GPIO1
6
GPIO2
7
PECI
8
VTT
VTT
9
TACH3
TACH3
10
11
12
13
14
PWM2 / #SMBALERT
TACH1
PWM2 / #SMBALERT
TACH1
TACH2
TACH2
PWM3 /#ADDREN
PWM3 /#ADDREN
TACH4/#THERM/#SMBALERT/
#ADDRESS SELECT
TACH4/#THERM/#SMBALERT/
#ADDRESS SELECT
15
16
17
18
19
20
21
22
23
24
D2−
D2−
D2+
D2+
D1−
D1−
D1+
GPIO3/#THERM/#SMBALERT
+5Vin
D1+
IMON
+5Vin
+12Vin
+12Vin
+2.5V / #THERM
Vccp
+2.5V / #THERM
Vccp
PWM1 / XTO
PWM1 / XTO
Functional Comparison between the NCT7491 and the ADT7490
• NCT7491 supports PECI 3.0 commands.
• The NCT7491 register map is organized into two pages.
0x00−0xFF (page 1) and 0x100−0x1FF (page 2)
• NCT7491 uses an SMBus Master port to read digital
• The NCT7491 supports PWM look−up table automatic
fan control along with the Tmin/Trange control method
used in the ADT7490
temperatures.
• I
voltage monitoring pin (pin 19) on the ADT7490
is replaced with digital pin
MON
• The NCT7491 allows temperatures to be written to the
device from an external master. These values can be
assigned for fan control and Limit/THERM assertion
functions
(SMBALERT/THERM/GPIO) on the NCT7491
• NCT7491 does not support Dynamic Tmin fan control.
• NCT7491 allows any combination of temperature
sources to control any fan.
• PECI fan control can be implemented in relative or
absolute modes. Absolute mode uses the Tjmax value
read from the CPU plus the PECI temperature to
determine the actual core temperature.
• The reference for voltage measurement has changed
from 2.25 V on the ADT7490 to 2 V on the NCT7491.
• NCT7491 allows individual PWM responses to
THERM events.
• NCT7491 THERM behaviour is more flexible,
allowing stepped response to THERM events.
• REPLACE mode for PECI is not supported by the
NCT7491
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NCT7491
Functional Block Diagram
Figure 2. Functional Block Diagram of NCT7491
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NCT7491
Typical System Connections
Figure 3. System Connection Diagram
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10
NCT7491
SMBus Slave Interface
the data line high after the 10th clock rising edge to assert a
stop condition. In read mode, the master device overrides the
acknowledge bit by floating the data line high during the low
period before the ninth clock pulse; this is known as No
acknowledge. The master takes the data line low during the
low period before the 10th clock rising edge, and then high
afetr the 10th clock rising edge to assert a stop condition.
In the NCT7491, write operations contain either one or
two bytes, and read operations contain one byte. To write
data to one of the device data registers or read data from it,
the address pointer register must be set so that the correct
data register is addressed. Then data can be written into that
register or read from it. The first byte of a write operation
always contains an address that is stored in the address
pointer register. If data is to be written to the device, the write
operation must contain a second data byte that is written to
the register selected by the address pointer register.
This write operation is shown in Figure 4. The device
address is sent over the bus, and then R/W is set to 0. This
is followed by two data bytes. The first data byte is the
address of the internal data register to be written to, which
is stored in the address pointer register. The second data byte
is the data to be written to the internal data register.
When reading data from a register, there are two
possibilities:
Control of the NCT7491 is carried out using the serial
system management bus (SMBus). The NCT7491 is
connected to this bus as a slave device, under the control of
a master controller. The NCT7491 has a 7−bit serial bus
address. When the device is powered up with the ADDREN
pin high, the NCT7491 has a default SMBus address of
0101110 or 0x2E. The read/write bit must be added to get the
8−bit address.
If more than one NCT7491 is to be used in a system, each
additional NCT7491 is placed in address select mode by
strapping ADDREN low on power−up. The logic state of the
ADDRESS SELECT pin then determines the device’s
SMBus address.
The device address is latched on the first valid SMBus
transaction, more precisely on the low−to−high transition at
the beginning of the eighth SCL pulse, when the serial bus
address byte matches the selected slave address. Any
attempted changes in the address have no effect after this.
SMBus Addressing Options
Table 5. SETTING THE SMBUS ADDRESS
ADDREN
pin state
ADDRESS SELECT
pin state
Address
0
0
1
Low (10 kW to GND)
High (10 kW pull−up)
Don’t care
0101100 (0x2C)
0101101 (0x2D)
0101110 (0x2E)
• If the NCT7491 address pointer register value is
unknown or not the desired value, it must first be set to
the correct value before data can be read from the
desired data register. This is done by performing a write
to the NCT7491 as before, but only the data byte
containing the register address is sent because no data is
written to the register. This is shown in Figure 5.
A read operation is then performed consisting of the
serial bus address, R/W bit set to 1, followed by the
data byte read from the data register. This is shown in
Figure 6.
Data is sent over the serial bus in sequences of nine clock
pulses: eight bits of data followed by an acknowledge bit
from the slave device. Transitions on the data line must
occur during the low period of the clock signal and remain
stable during the high period, because a low−to−high
transition when the clock is high may be interpreted as a stop
signal. The number of data bytes that can be transmitted over
the serial bus in a single read or write operation is limited
only by what the master and slave devices can handle.
When all data bytes have been read or written, stop
conditions are established. In write mode, the master floats
• If the address pointer register is known to be already at
the desired address, data can be read from the
corresponding data register without first writing to the
address pointer register, as shown in Figure 6.
1
9
1
9
SCL
D6
D2
SDA
START BY
0
1
0
1
1
1
0
D7
D5
D4
D3
D1
D0
R/W
ACK. BY
ADT7490
ACK. BY
ADT7490
MASTER
FRAME 1
SERIAL BUS ADDRESS BYTE
FRAME 2
ADDRESS POINTER REGISTER BYTE
1
9
SCL (CONTINUED)
SDA (CONTINUED)
D5
D4
D3
D2
D1
D0
D7
D6
STOP BY
MASTER
ACK. BY
ADT7490
FRAME 3
DATA BYTE
Figure 4. Writing a Register Address to the Address Pointer Register, then Writing Data to the Selected Register
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11
NCT7491
1
0
9
1
9
SCL
SDA
D6
D2
1
0
1
1
1
0
D7
D5
D4
D3
D1
R/W
D0
ACK. B Y
ADT7490
START B Y
MASTER
ACK. B Y
ADT7490
STOP BY
MASTER
FRAME 1
SERIAL BUS ADDRESS BYTE
FRAME 2
ADDRESS POINTER REGISTER BYTE
Figure 5. Writing to the Address Pointer Register Only
1
0
9
1
9
SCL
D6
D2
1
0
1
1
1
0
D7
D5
D4
D3
D1
R/W
D0
SDA
START B Y
ACK. B Y
ADT7490
NO ACK. B Y STOP BY
MASTER MASTER
MASTER
FRAME 1
SERIAL BUS ADDRESS BYTE
FRAME 2
DATA BYTE FROM ADT7490
Figure 6. Reading Data from a Previously Selected Register
It is possible to read a data byte from a data register without
first writing to the address pointer register if the address
pointer register is already at the correct value. However, it
is not possible to write data to a register without writing to
the address pointer register because the first data byte of a
write is always written to the address pointer register.
In addition to supporting the send byte and receive byte
protocols, the NCT7491 also supports the read byte protocol
(see System Management Bus Specifications Rev. 2 for more
information; this document is available from the SMBus
organization).
6. The master asserts a stop condition on SDA and
the transaction ends.
For the NCT7491, the send byte protocol is used to write
a register address to RAM for a subsequent single−byte read
from the same address. This operation is illustrated in Figure 7.
1
2
3
4
5
6
SLAVE
ADDRESS
REGISTER
ADDRESS
S
W
A
A
P
Figure 7. Setting a Register Address for
Subsequent Read
If several read or write operations must be performed in
succession, the master can send a repeat start condition
instead of a stop condition to begin a new operation.
If the master is required to read data from the register
immediately after setting up the address, it can assert a repeat
start condition immediately after the final ACK and carry
out a single−byte read without asserting an intermediate stop
condition.
Write Operations
The SMBus specification defines several protocols for
different types of read and write operations. The ones used
in the NCT7491 are discussed here. The following
abbreviations are used in the diagrams:
Write Byte
In this operation, the master device sends a command byte
and one data byte to the slave device, as follows:
1. The master device asserts a start condition on SDA.
2. The master sends the 7−bit slave address followed
by the write bit (low).
• S – Start
• P – Stop
• R – Read
• /W – Write
3. The addressed slave device asserts ACK on SDA.
4. The master sends a command code.
5. The slave asserts ACK on SDA.
• A – Acknowledge
• /A – No acknowledge
The NCT7491 uses the following SMBus write protocols.
6. The master sends a data byte.
7. The slave asserts ACK on SDA.
8. The master asserts a stop condition on SDA, and
the transaction ends.
Send Byte
In this operation, the master device sends a single
command byte to a slave device, as follows:
1. The master device asserts a start condition on SDA.
2. The master sends the 7−bit slave address followed
by the write bit (low).
The byte write operation is illustrated in Figure 8.
1
2
3
4
5
6
7
8
SLAVE
ADDRESS
REGISTER
ADDRESS
S
W
A
A
DATA
A
P
3. The addressed slave device asserts ACK on SDA.
4. The master sends a command code.
5. The slave asserts ACK on SDA.
Figure 8. Single Byte Write to a Register
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NCT7491
Read Operations
The NCT7491 uses the following SMBus read protocols.
the bus is locked and releases the bus. This prevents the
device from locking or holding the SMBus expecting data.
Some SMBus controllers cannot work with the SMBus
timeout feature, so it can be disabled.
Register 0x11 <4> TODIS = 0, SMBus timeout enabled
(default). <4> TODIS = 1, SMBus timeout disabled.
Receive Byte
This operation is useful when repeatedly reading a single
register. The register address must be previously set up. In
this operation, the master device receives a single byte from
a slave device, as follows:
Register Map Paging
1. The master device asserts a start condition on SDA.
2. The master sends the 7−bit slave address followed
by the read bit (high).
3. The addressed slave device asserts ACK on SDA.
4. The master receives a data byte.
5. The master asserts NO ACK on SDA.
6. The master asserts a stop condition on SDA, and
the transaction ends.
The NCT7491 register map is organized into two pages:
• Page 1 contains register addresses 0x00 to 0xFF
• Page 2 contains register addresses 0x100 to 0x1FF
The default page on power up is page 1, so any SMBus
read/writes to the NCT7491 will be to addresses in the range
0x00−0xFF.
To access page 2 of the register map, bit 0 (RGMP) of
register 0xFF must be set to 1. Any subsequent read/writes
after that bit is set will be to addresses in the range 0x100 to
0x1FF, e.g. reading from address 0x22 when RGMP is set
will read from register 0x122. Bit 0 of register 0xFF is, in
effect, the MSb of the address pointer. To return to page 1,
bit 0 (RGMPCL) of register 0x1FF must be cleared to 0.
All register read/writes referenced in this document refer
to registers on SMBus Page 1 unless stated otherwise.
In the NCT7491, the receive byte protocol is used to read
a single byte of data from a register whose address has
previously been set by a send byte or write byte operation.
This operation is illustrated in Figure 9.
1
2
3
4
5
6
SLAVE
ADDRESS
S
R
A
DATA
A
P
Analog Temperature Measurement
A simple method of measuring temperature is to exploit
the negative temperature coefficient of a diode connected
transistor, measuring the base emitter voltage (V ) of a
transistor operated at constant current. However, this
technique requires calibration to null the effect of the
Figure 9. Single−Byte Read from a Register
Alert Response Address
Alert response address (ARA) is a feature of SMBus
devices that allows an interrupting device to identify itself
to the host when multiple devices exist on the same bus.
The SMBALERT output can be used as either an interrupt
output or an SMBALERT. One or more outputs can be
connected to a common SMBALERT line connected to the
master. If a device’s SMBALERT line goes low, the
following events occur:
BE
absolute value of V , which varies from device to device.
BE
The technique used in the NCT7491 measures the change
in V when the device operates at four different currents.
BE
Figure 10 shows the input signal conditioning used to
measure the output of an external temperature sensor. This
figure shows the external sensor as a substrate transistor, but
it can equally be a discrete transistor. If a discrete transistor
is used, the collector is not grounded but is linked to the base.
To prevent ground noise interfering with the
measurement, the more negative terminal of the sensor is not
referenced to ground, but is biased above ground by an
internal diode at the D− input. C1 may be added as a noise
filter (a recommended maximum value of 1000 pF).
However, a better option in noisy environments is to add a
filter, as described in the Noise Filtering section.
1. SMBALERT is pulled low.
2. The master initiates a read operation and sends the
alert response address (ARA = 0001 100). This is
a general call address that must not be used as a
specific device address.
3. The device whose SMBALERT output is low
responds to the alert response address, and the
master reads its device address. The address of the
device is now known and can be interrogated in
the usual way.
To measure DV , the operating current through the
4. If more than one device’s SMBALERT output is low,
the one with the lowest device address has priority
in accordance with normal SMBus arbitration.
5. Once the NCT7491 has responded to the alert
response address, the master must read the status
registers, and the SMBALERT is cleared only if
the error condition is gone.
BE
sensor is switched among 4 currents, 2 x 2 related currents.
As shown in Figure 10, N1 x I is a multiple of I and N2 x
1
1
I is a multiple of I . The currents through the temperature
2
2
diode are switched between I and N1 x I, giving DV ; and
BE1
then between I and N2 x I, giving DV . The temperature
BE2
is then calculated using the two DV measurements. This
BE
method cancels the effect of any series resistance on the
temperature measurement.
SMBus Timeout
The NCT7491 includes an SMBus timeout feature. If
there is no SMBus activity for 25 ms, the NCT7491 assumes
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NCT7491
Figure 10. Analog Temperature Measurement Method
Series Resistance Cancellation
ensures that the results read back from the two registers
come from the same measurement.
Parasitic resistance to the D+ and D− inputs to the
NCT7491, seen in series with the remote diode, is caused by
a variety of factors, including PCB track resistance and track
length and internal resistance in the CPU. This series
resistance appears as a temperature offset in the remote
sensor’s temperature measurement. This error typically
causes a 0.5 degree C offset per ohm of parasitic resistance
in series with the remote diode.
The NCT7491 automatically cancels the effect of this series
resistance on the temperature reading, giving a more accurate
result, without the need for user characterization of this
resistance. The NCT7491 is designed to automatically cancel
typically up to 270 W of resistance in series with the thermal
diode. By using an advanced temperature measurement
method, this process is transparent to the user. This feature
permits resistances to be added to the sensor path to produce
a filter, allowing the part to be used in noisy environments.
Theoretically, the temperature sensor and ADC can
measure temperatures from −64°C to +127.5°C with a
resolution of +0.25°C. However, this exceeds the operating
temperature range of the device, so local temperature
measurements outside the NCT7491 operating temperature
range are not possible.
• Remote1 result registers: 0x25 (MSB), 0x77 bits <3:2>
(2 LSb)
• Local result registers: 0x26 (MSB), 0x77 bits <5:4>
(2 LSb)
• Remote1 result registers: 0x27 (MSB), 0x77 bits <7:6>
(2 LSb)
Table 6. TWO’S COMPLEMENT FORMAT
Temperature
−64°C
Digital Output (10−Bit)
1100 0000 00
1100 1001 00
1101 1000 00
1111 0110 00
1111 1111 00
Temperature Measurement Results
−55°C
The results of the Local, Remote 1 and Remote 2 temperature
measurements are stored in the local (0x26), remote 1 (0x25)
and remote 2 (0x27) temperature value registers in two’s
complement format or Offset 64 format, depending on bit 0
if register 0x7C (1= 2’s complement, 0 = Offset 64). These
results are then compared with limits programmed into the
local, remote 1 and remote 2 high and low limit registers.
The high, low and THERM limits for the local, remote 1 and
remote 2 channels must be in the same format as the
temperature reading i.e. 2’s complement or Offset 64.
All the temperature measurement data for each channel is
stored in two registers, one for the MSB and one for the LSB.
This gives the temperature measurement resolution of
0.25°C. When reading the full external temperature value,
read the LSB first. This causes the MSB to be locked (that
is, the ADC does not write to it) until it is read. This feature
−40°C
−10°C
−1°C
−0.25°C
0°C
1111 1111 11
0000 0000 00
0000 1010 01
0001 1001 00
0111 1101 00
0111 1111 10
0111 1111 11
10.25°C
25°C
125°C
127.5°C
Diode Fault – 127.75
NOTE: Bold numbers denote the LSB bits from
extended resolution register 0x77.
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NCT7491
Offset 64 Format
• Local Low Limit register: 0x50
• Local High Limit register: 0x51
• Remote2 Low Limit register: 0x52
• Remote2 High Limit register: 0x53
In Offset 64 mode the range of values monitored is −64°C
to 191.5°C (as opposed to −64°C to +127.5°C in 2’s
complement mode). To read the temperature in this format
the user must subtract 64 from the value returned from the
temperature register. Offset 64 mode is enabled by setting bit
0 if register 0x7C to zero.
Offset Registers
Offset errors can be introduced into the temperature
measurements by clock noise or when the thermal diode is
located away from the hot spot. To achieve the specified
accuracy on this channel, these offsets must be removed.
The offset value is stored as an 8−bit, twos complement
value. The value in the offset register is added to, or
subtracted from, the measured value of the relevant
temperature. The offset register has a default value of 0°C
and has no effect unless the user writes a different value to
it. The resolution of the value in the offset register is
determined by bit 1 of register 0x7C. If the bit is 0 then the
resolution is 0.5°C. If the bit is 1 then the resolution is 1°C.
Table 7. OFFSET64
Register Code
Temperature
−64°C
−32°C
0°C
0
32
64
100
255
36°C
191°C
Round Robin Temperature Measurement
• Remote1 Offset, register 0x70
• Local Offset, register 0x71
• Remote2 Offset, register 0x72
The local and remote sensors are read in sequence in a
continuous loop when monitoring is enabled (setting bit 0 of
register 0x40). The user may decide which temperature
channels are included in the monitoring loop using bits
<2:0> in register 0x13.
Push Registers
• Setting <0> of register 0x13 includes the local channel
in the monitoring loop.
• Setting <1> of register 0x13 includes the remote1
channel in the monitoring loop.
The NCT7491 allows the user to program 4 temperatures
into the device that can then be used for fan control and
THERM/SMBALERT functions in the same way as other
temperature sources. These temperatures can be written by
the system SMBus master and should be programmed as 2’s
complement values.
• Setting <2> of register 0x13 includes the remote2
channel in the monitoring loop.
• Push0, register 0xC8
Any channel not required in an application should be
removed from the loop to reduce the overall monitoring
time. Voltage channels may also be selected for the
monitoring loop. See the Voltage Monitoring section for
more information.
• Push1, register 0xC9
• Push2, register 0xCA
• Push3, register 0xCB
Push Limit Registers
There are high, low and THERM limits associated with the
Push channels. The same limits are applied to all 4 channels.
• Push Low Limit register, 0xCF
• Push High limit register, 0xCE
• Push THERM Limit register, 0xD0
Temperature Averaging
The number of samples over which the temperature
readings (and voltage readings) are averaged is set by bits
<7:6> of register 0x40. The options are:
• 4 samples per averaged reading, <7:6> = <00>
• 8 samples per averaged reading, <7:6> = <01>
• 16 samples per averaged reading, <7:6> = <10>
• 32 samples per averaged reading, <7:6> = <11>
Averaging can be disabled for temperature readings by
setting bit <4> of register 0x73.
Push Tmin/Trange Registers
The Push channels also have associated Tmin/Trange
values for Automatic Fan Control. The hysteresis applied at
the Tmin value can also be programmed.
• Push Tmin, 0xCC
Temperature Limits
• Push Trange, 0xCD bits <3:0>
• Push Hysteresis, 0xEB bits <3:0>
Temperature limits can be set for each channel to detect an
out of limit condition. These registers are programmed in the
same format as the temperature reading, so if Offset64 mode
is enabled then these registers must be programmed in that
format, otherwise theay are programmed as 2’s
complement.
• Remote1 Low Limit register: 0x4E
• Remote1 High Limit register: 0x4F
PECI 3.0 Interface
The PECI 3.0 interface reads thermal data from the up to
4 CPUs located at PECI addresses between 0x30 and 0x37
(the first 4 addresses populated are used), and from 1 or 2
domains per CPU. The hottest reading from the domains for
each CPU is stored in the PECI temperature registers. It can
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NCT7491
also write thermal data to the Package Configuration Space
in the CPU. A PECI reading is a negative value, in degrees
Celsius, which represents the offset from the thermal control
also be set to indicate that at least one CPU was detected. If
any processors are detected then the PECI monitoring loop
will automatically start.
circuit (T ) activation temperature. PECI information is
The Vccp pin must be connected to an input voltage for the
PECI interface to function correctly. If it is not connected to
the CPU supply voltage then it should be connected to the
NCT7491 supply voltage, Vcc. If the system processor does
not support PECI 3.0 then the PECI monitoring loop will not
automatically start. In that case the user can write to the
PECI registers to manually configure the interface. The
register descriptions are given below.
CC
returned as a 16−bit 2’s complement value from which the
8−bit 2’s complement value is derived. See the Platform
Environment Control Interface (PECI) Specification from
Intel for more details on the PECI data format. The PECI
temperature stored for each CPU is an averaged value; the
averaging window is user programmable.
The NCT7491 automatically detects the presence of a
CPU at each of the supported addresses, and also detects the
number of supported domains for each CPU. The presence
of each CPU is indicated in the NCT7491 status registers.
On power up, the PECI interface will become active when
the voltage measured on VTT is above 0.5 V and the voltage
on Vccp is above 0.5 V. The returned CPU temperature will
determine the behavior of the fans on power−up.
PECI Error Detection
The PECI 3.0 protocol includes FCS (Frame Check
Sequence) bytes to guarantee data integrity. If there is a
mismatch between the data and the FCS then a status bit
indicates the communication failure (COMM status bit,
register 0x43 bit <2>). PECI 3.0 also supports processor
specific error codes to indicate error conditions relating to
the temperature sensor within the processor (DATA status
bit, register 0x43 bit <1>). These codes are shown in
Table 8:
Thermal data that is collected by the NCT7491 (e.g. the
DIMM temperatures) can be written to the CPU’s Package
Configuration Space (PCS) over the PECI 3.0 interface.
This data can be used by the CPU to modify memory
operations based on the DIMM temperature.
Table 8. DATA ERROR CODES
There are associated high and low limits for each PECI
reading that can be programmed. The limit values take the
same format as the PECI reading. Therefore, the
programmed limits are not absolute temperatures but a
relative offset in degrees Celcius from the TCC activation
temperature. An out−of−limit event is recorded as follows:
DATA code bits
<6:4>, 0x43
DATA
Error code
Description
<000>
<001>
0x8000
0x8002
General Sensor Error
Temperature below
operational range
• High Limit > comparison performed
• Low Limit ≤ comparison performed
<010>
0x8003
Temperature above
operational range
An out−of−limit event is recorded in the associated status
register and can be used to assert the SMBALERT pin.
A generic PECI 3.0 interface command structure is also
available to allow an external master to issue any PECI 3.0
command in addition to the commands implemented by the
NCT7491 monitoring loops.
PECI Completion Code
Each read or write operation to the CPU Package
Configuration Space returns a completion code to indicate
the success or failure of the operation. The completion codes
supported are shown in Table 9:
Table 9. COMPLETION CODES
Completion
PECI VTT Input
The PECI V voltage is used as the reference voltage for
TT
Code
the PECI interface. This voltage must be connected to the
NCT7491 in order for the PECI interface to be operational.
Description
0x40
0x80
Command Passed, data is valid
The PECI V input is also monitored by the NCT7491 and
TT
Command timed out. Processor cannot gener-
ate required response in a timely fashion.
Retry is appropriate.
has associated high and low limits to allow out−of–limit
detection on the V channel. The valid operational voltage
TT
range for PECI V is 0.85 V to 1.26 V.
TT
0x81
Command timed out. Processor cannot alloc-
ate resources for the request. Retry is appro-
priate.
PECI Startup Operation
On power up of the NCT7491 the PECI V pin and the
TT
0x90
0x91
Unknown/Invalid/Illegal request
Vccp pin are monitored. If the voltage on both of these pins
rises above 0.5 V then the NCT7491 will wait 5 ms and then
automatically scan the PECI port to check for the presence
of PECI 3.0 enabled processors. For any processors that are
detected the PECI address, the domain count, the Tcontrol
value and the Tjmax value will be read and stored in the
NCT7491. The CPU count bits will be set (bits <7:6> of
register 0x88). The PDET bit (bit <0> 0f register 0x37) will
PECI Control hardware, firmware or associ-
ated logic error. The processor cannot process
the request.
The completion code status bit in the NCT7491 (register
0x81 bit <0>) indicates the result of each read/write
operation.
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NCT7491
PECI Registers
PECI CPU Addresses:
The registers relating to the operation of the PECI 3.0
interface are as follows:
• PECI0 CPU Address, 0x00
• PECI1 CPU Address, 0x01
• PECI2 CPU Address, 0x02
Enabling the Interface:
• PECI Monitor, 0x40 bit 4
• PECI3 CPU Address, 0x03
Setting PECI Monitor to 1 enables the PECI temperature
monitoring loop. This will be automatically enabled on
These are the addresses used to access each CPU on the
PECI interface and are automatically populated by the
NCT7491 on power up. The values can be overwritten by the
user.
power up if the V and V
voltages have exceeded preset
TT
CCP
thresholds and any PECI 3.0 enabled processors have been
automatically detected.
PECI Temperature Values:
• PECI0 Temperature, 0x33
• PECI1 Temperature, 0x1A
• PECI2 Temperature, 0x1B
NOTE: The PDET bit (bit <0> 0x37) must also be set
for correct operation.
Detected number of CPUs:
• CPU Count, 0x88 bits <7:6>
• PDET, 0x37 <0>
• PECI3 Temperature, 0x1C
These are the relative temperature values returned by the
CPU. If a CPU is not populated then its associated
temperature register can be written to by an external master.
Data is tored in 2’s complement format.
CPU Count indicates the number of populated CPUs.
CPUs are automatically detected on power up by the
NCT7491 and the number found is set here. The number can
be overwritten by the user and sets the number of CPUs to
be included in the temperature monitoring loop. The number
of CPUs is 1 to 4, and the format is as shown in Table 10.
PDET is set if at least one PECI enabled processor is
detected. If it is not automatically set then it must be set by
the user.
PECI Absolute Temperature Values:
• PECI0_Abs Temperature, 0x04
• PECI1_Abs Temperature, 0x05
• PECI2_Abs Temperature, 0x06
• PECI3_Abs Temperature, 0x07
These are the absolute CPU temperature values. They are
automatically calculated by the NCT7491 from the relative
Table 10. CPU COUNT
0x88 <7:6>
<00>
CPU Count
temperature and the CPU T
value. See the PECI
JMAX
1
2
3
4
T
JMAX
Values section. Data is stored in unsigned format.
<01>
Absolute PECI mode
<10>
The user can enable Absolute PECI mode by setting bit 2
of register 0x73 (ABS/REL) which will use the value stored
in the PECI absolute temperature registers for fan control,
THERM behaviour and SMBALERT behaviour rather than
the relative PECI values.
<11>
Domain Count bits:
• DOM0, 0x36 bit 3
• DOM1, 0x88 bit 5
• DOM2, 0x88 bit 4
• DOM3, 0x88 bit 3
PECI Averaging
The number of samples over which the PECI master will
calculate an averaged temperature reading for each CPU can
be set in register 0x36, bits <2:0>:
• <000> = No averaging
• <001> = Averaged over 2 samples
• <010> = Averaged over 4 samples
• <011> = Averaged over 8 samples
• <100> to <111> are reserved
These bits indicate the number of supported domains per
CPU (0 = 1 domain, 1 = 2 domains). THE NCT7491
automatically detects these values on power up and sets the
appropriate bits. They can be overwritten by the user.
PECI Interval:
• PECI Update Rate, 0x37 bits <5:4>
This determines the rate at which the PECI temperature
registers are updated.
PECI Offsets:
• PECI0 Offset, 0x94
• PECI1 Offset, 0x95
• PECI2 Offset, 0x96
Table 11. UPDATE RATE
0x37 <5:4>
<00>
PECI Update Rate
1/sec
• PECI3 Offset, 0x97
Offset values can be assigned to each temperature channel
by programming these registers. The value programmed
should be in 2’s complement format. The resolution is 1°C.
<01>
2/sec
<10>
5/sec
<11>
10/sec
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NCT7491
PECI Limits:
The user can choose to use the relative or absolute PECI
temperature values for fan control. If Absolute PECI mode
is used then the maximum valid Tmin value is 175°C.
For full details on the Fan Control implementation see the
‘Fan Control’ section of this document
• PECI Low Limit, 0x34
• PECI High Limit, 0x35
These registers are used to set the allowable PECI
temperature range. If the temperature is above the high limit
or below the low limit then a status bit is set and pins
configured as SMBALERT will assert. The high and low
limit values are common to all PECI channels. The format
depends on whether Absolute PECI mode is enabled. If it is
then the limits are in unsigned format. If Absolute PECI
mode is not enabled then the format is 2’s complement.
PECI Status Bits:
• PECI0 limit error, 0x43 bit 0
• PECI1 limit error, 0x81 bit 3
• PECI2 limit error, 0x81 bit 4
• PECI3 limit error, 0x81 bit 5
• DATA error, 0x43 bit 1
• COMM error, 0x43 bit 2
• DATA type, 0x43 bits <6:4>
• PECI completion code, 0x81 bit 0
PECI T
Values:
CONTROL
• PECI0 T
• PECI1 T
• PECI2 T
• PECI3 T
, 0x3D
CONTROL
CONTROL
CONTROL
CONTROL
, 0x08
, 0x09
, 0x0A
• PECI0 T
• PECI1 T
• PECI2 T
• PECI3 T
exceeded, 0x89 bit 0
exceeded, 0x89 bit 1
exceeded, 0x89 bit 2
exceeded, 0x89 bit 3
CONTROL
CONTROL
CONTROL
CONTROL
These values set the fail−safe fan assertion temperature.
The response of the fans is determined by the THERM
configuration registers and is described in the ‘THERM
Assertion’ section of this document. These values can be
read from the CPU via the PECI interface or programmed
directly by the user.
The Data Type field indicates the returned code if a DATA
error is generated. Status bits in 0x43 and 0x81 can be
masked by setting the corresponding mask bits in registers
0x82 and 0x83.
The format depends on whether Absolute PECI mode is
enabled. If it is then the limit is in unsigned format. If
Absolute PECI mode is not enabled then the format is 2’s
complement.
Generic PECI Command Block
• CPU Address, 0xD1
• Data Write Length, 0xD2
• Data Read Length, 0xD3
PECI T
Values:
JMAX
• PECI0 T
• PECI1 T
• PECI2 T
• PECI3 T
, 0x0B
JMAX
JMAX
JMAX
JMAX
• Data Write Buffer, 0xD4 to 0xE0
• Data Read Buffer, 0xE1 to 0xE9
, 0x0C
, 0x0D
, 0x0E
• Generic PECI Configuration, 0xEA
These registers define the generic PECI interface. An
external master can populate these registers in order to
execute any supported PECI 3.0 commands.
Each CPU has a maximum junction temperature T
.
JMAX
These values for the populated CPUs are read via the PECI
3.0 interface by the NCT7491. They can also be
over−written by the user. They are used to determine the
absolute PECI temperature. These values are stored as
unsigned data.
The byte definitions for this block are as follows:
CPU Address sets the target address of the PECI client that
is to be accessed.
PECI Fan Control:
• PECI Tmin, 0x3B
Data Write Length sets the number of bytes to be
transferred to the PECI client. This byte should include the
AW FCS byte in its count. The AW FCS byte is
automatically calculated and appended by the NCT7491.
• PECI Trange, 0x3C bits <7:4>
• PWM1 Source1, 0x8A bits <6:3>
• PWM2 Source1, 0x8D bits <6:3>
Data Read Length sets the number of bytes to be returned
from the PECI client.
• PWM3 Source1, 0x90 bits <6:3>
Data Write Buffer is a 13 byte buffer that holds the data to
be transferred to the client. The first byte of this buffer is the
command code that defines the command to be executed.
Tmin sets the turn−on temperature for any fan that is
controlled by a PECI temperature.
Trange sets the range over which the PWM output will
increase from PWMmin to PWMmax.
Data Read Buffer is a 9 byte buffer that will hold the data
returned from the client.
The PECI Tmin and PECI Trange values are common to
all PECI channels.
The PWMX Source registers are used to assign
temperature control to a fan. The PECI assignment is done
with bits <6:3> in those registers.
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The PECI Configuration 5 register (address 0xEA)
functions. Enabling the SMBus master port overrides any
GPIO1/GPIO2 configuration settings.
enables the generic block and allows the command to be
executed. The configuration bits are:
• AW, bit 1
SMBus Compatible Master Registers
The registers relating to the control of the SMBus
compatible master interface are as follows:
• PEX, bit 2
Setting AW to 1 indicates that the transfer is an Assured
Write transaction.
Enabling the SMBus Master port:
• SMBus Master Enable, 0xB5 bit 0
Setting PEX to 1 causes the NCT7491 to execute the
command that has been set up in the generic command
block. This bit will automatically clear when the transaction
has completed.
If a communication error occurs when a Generic PECI
command is sent then the GCOMM status bit is set. This bit
can be masked.
Setting this bit configures pins 5 and 6 on the QSOP
package, or pins 2 and 3 on the QFN package as the SMBus
Master Port. It also enables the Thermal slave temperature
monitoring loop which will gather data from the devices
configured in the SMBus Master Addressing table.
When this bit is 0 and pins 5 and 6 on the QSOP package,
or pins 2 and 3 on the QFN package are not configured as
GPIOs then the SMBus slave port is internally connected to
the SMBus master port. This allows the master connected to
the NCT7491 to communicate directly with devices that are
on the NCT7491 master port.
• GCOMM, register 0x81 <2>
• GCOMM mask, register 0x83 <2>
SMBus Compatible Master Port
Thermal data is gathered from temperature monitoring
devices attached to the SMBus Master port on the NCT7491.
This port is used to automatically read temperature data
from DIMM sensors, the PCH chipset sensor, graphics
thermal sensors, or any thermal sensor with an SMBus
interface. Up to 8 thermal slave devices are supported on the
SMBus master port. The SMBus slave address for each
device is user programmable. The register address of the
thermal data within the slave device is also user
programmable. This is assumed to be a 1−byte address so
devices with a register address range of 0x00 to 0xFF are
suitable. Each slave device has associated programmable
configuration bits to indicate the protocol required to
communicate over the SMBus and the temperature data
format returned by the slave device. Status bits will indicate
if any checksum errors arise from communicating with the
slave devices.
The NCT7491 can be connected to the SMLINK1 port of
the PCH to allow the PCH thermal data to be read. Data is
automatically read from the PCH using the SMBus Block
Read protocol. The device can be configured to read the
DIMM temperature registers from the PCH.
The SMBus master and slave ports on the NCT7491 can
be connected together if required.
Temperature readings returned from the thermal devices
on the SMBus master port are available for use in the
Automatic Fan Control algorithm.
Temperature Addressing Table:
• Device0 Address, 0x98
• Device0 Pointer, 0x99
• Device1 Address, 0x9A
• Device1 Pointer, 0x9B
• Device2 Address, 0x9C
• Device2 Pointer, 0x9D
• Device3 Address, 0x9E
• Device3 Pointer, 0x9F
• Device4 Address, 0xA0
• Device4 Pointer, 0xA1
• Device5 Address, 0xA2
• Device5 Pointer, 0xA3
• Device6 Address, 0xA4
• Device6 Pointer, 0xA5
• Device7 Address, 0xA6
• Device7 Pointer, 0xA7
The DeviceX Address register sets the 7−bit (R/W bit not
included) SMBus address of the thermal sensor.
The DeviceX Pointer register sets the register address of
the temperature data in the thermal slave device.
Device0 can be used for SMBus Block Read commands.
In that case the block read command code should be written
to the Device0 Pointer register. If the NCT7491 Master port
is connected to the SMLINK1 port of the Intel PCH then the
PCH temperature (and possibly the DIMM temperatures)
can be read from this port. In that case Device0 should be
reserved for the PCH temperature and Device1 to Device 4
reserved for DIMM0 to DIMM3.
The SMBus thermal devices have associated high and low
temperature limit registers to allow out−of−limit conditions
to be detected. If the SMBus Master interface is disabled
then the SMBus master is internally connected to the slave
interface, if the pins have not been assigned to GPIO
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The NCT7491 will not attempt to read from a device that
has a Device Address byte that is set to 0.
Table 15. Device3 FORMATS
0xB2 <7:6>
Format
Temperature Values:
00
2’s Complement
• Device0 (PCH), 0xA8
• Device1 (DIMM0), 0xA9
• Device2 (DIMM1), 0xAA
• Device3 (DIMM2), 0xAB
• Device4 (DIMM3), 0xAC
• Device5, 0xAD
01
10
11
JEDEC SPD standard
Unsigned binary
reserved
Table 16. Device4 FORMATS
0xB3 <1:0>
Format
• Device6, 0xAE
00
2’s Complement
• Device7, 0xAF
01
10
11
JEDEC SPD standard
Unsigned binary
reserved
The results of the readings from each of the thermal slave
devices are stored here.
Thermal Slave Data Formats
It is necessary for the NCT7491 to be configured so that
the data format for each SMBus client device is known, e.g.
if the data is 2’s Complement or unsigned data, or if a JEDEC
standard SPD device is used so that the data can be correctly
read from the device. Each SMBus device has a bit field to
determine the data format for that device. The format
selected for the device determines its behaviour for
out−of−limit comparisons, THERM assertions and fan
control operation. For Device0, if the format is set to PCH
Block Read then the resulting data is stored as unsigned
binary. The VR12 literal mode can be selected to allow
temperature or power data be read from a VR12 controller
via the PMBus.
Table 17. Device5 FORMATS
0xB3 <3:2>
Format
00
2’s Complement
01
10
11
JEDEC SPD standard
Unsigned binary
VR12 Literal
Table 18. Device6 FORMATS
0xB3 <5:4>
Format
00
2’s Complement
01
10
11
JEDEC SPD standard
Unsigned binary
VR12 Literal
Table 12. Device0 FORMATS
0xB2 <1:0>
Format
00
01
10
11
2’s Complement
JEDEC SPD standard
Unsigned binary
PCH block reads
Table 19. Device7 FORMATS
0xB3 <7:6>
Format
00
2’s Complement
01
10
11
JEDEC SPD standard
Unsigned binary
VR12 Literal
Table 13. Device1 FORMATS
0xB2 <3:2>
Format
00
2’s Complement
SMBus Master Update Rate
The interval between successive reads from an SMBus
client device is determined by register 0xC7 bits <7:6>:
01
10
11
JEDEC SPD standard
Unsigned binary
reserved
Table 20. SMBus UPDATE
0xC7 bits <7:6>
SMBus Update Rate
250 ms
Table 14. Device2 FORMATS
00
01
10
11
0xB2 <5:4>
Format
500 ms
00
2’s Complement
750 ms
01
10
11
JEDEC SPD standard
Unsigned binary
reserved
1 sec
Thermal Slave Limits:
• SMB Slave High Limit, 0xC1
• SMB Slave Low Limit, 0xC2
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NCT7491
These registers are used to set the allowable Thermal slave
If 0xB5 <5> is 1 then registers 0xA9 and 0xAA are
overwritten by the Remote1 temperature reading.
If 0xB5 <6> is 1 then registers 0xAB and 0xAC are
overwritten by the Remote2 temperature reading.
If bit 7 of 0xB5 (DIMM from PCH) is set then bits 5 and
6 have no effect.
temperature range. If the temperature is above the high limit
or below the low limit then a status bit is set and pins
configured as SMBALERT will assert. The high and low
limit values are common to all SMBus Thermal slave
readings. The low limit is programmed as a 2’s Complement
value. The high limit is programmed as an unsigned value.
The difference between the two formats is necessary to cover
the alternate formats available for the SMBus slave devices.
Writing DIMM temperatures to the CPUs
The DIMM temperatures collected from SPD devices,
from the PCH or from the analog thermal sensors can be
automatically written to the CPU via PECI. To enable this
function set the PWEN bit, register 0x37 <7>. The
temperatures written will be the maximum DIMM
temperature for each CPU.
Thermal Slave THERM Value:
• SMBus THERM Limit, 0xC3
This value sets the fail−safe THERM assertion
temperature. The response of the fans is determined by the
THERM configuration registers and is described in the
‘THERM Assertion’ section of this document. This value is
programmed as an 8−bit unsigned value.
DIMM CPU assignments:
• DIMM0 CPU, 0x0F bits <1:0>
• DIMM1 CPU, 0x0F bits <3:2>
• DIMM2 CPU, 0x0F bits <5:4>
Thermal Slave Fan Control:
• SMB Device Tmin, 0xC6
• SMB Device Trange, 0xC7 bits <3:0>
• PWM1 Source2, 0x8B
• PWM2 Source2, 0x8E
• PWM3 Source2, 0x91
• DIMM3 CPU, 0x0F bits <7:6>
These bits set the CPU associated with each DIMM. This
information is necessary in order for the PECI loop to
program the maximum DIMM temperature for each CPU.
Selecting DIMMs To Be Written
Tmin sets the turn−on temperature for any fan that is
controlled by a Thermal slave device. Trange sets the
temperature range over which the PWM output will increase
from PWMmin to PWMmax. The Tmin and Trange values
apply to all Thermal slave devices. SMB Tmin is
programmed as an 8−bit unsigned value. The maximum
valid SMBus Tmin value is 175°C.
The PWMX Source registers are used to assign
temperature control to a fan.
For full details on the Fan Control implementation see the
‘Fan Control’ section of this document.
Each DIMM register can be enabled to be written to the
CPU individually. This is done in register 0x87 bits <7:4>.
If a DIMM is not populated then the corresponding bit in this
register should be set to zero:
Setting 0x87 bit <4> to 1 includes DIMM0 in the PECI write
Setting 0x87 bit <5> to 1 includes DIMM1 in the PECI write
Setting 0x87 bit <6> to 1 includes DIMM2 in the PECI write
Setting 0x87 bit <7> to 1 includes DIMM3 in the PECI write
SMBus Thermal Slave Error Response
How the NCT7491 responds to errors on the SMBus
master port can be configured in the following ways:
SMBus Master Communication Settings
• Repeated Start Enable, 0xB0 bits <7:0>
• SMBus Retry Interval, 0x10 bits <4:3>
• PWM1 Response, 0x11 bit 5
• PWM2 Response, 0x11 bit 6
• PWM3 Response, 0x11 bit 7
• PEC Supported, 0xB1 bits <7:0>
The Repeated Start bits enable/disable the repeated start
protocol for each device.
The PEC Supported bits can be set if an SMBus client
device supports CRC−8 PEC. If this bit is set for a client
device then the NCT7491 will read the PEC byte after the
data and set the corresponding bit in the PEC status register
(0xB7) if the PEC byte is incorrect.
SMBus Retry Interval: If an error is encountered when
communicating with a Thermal slave device then the
NCT7491 will attempt to carry out the command up to 3
times. These bits set the interval between the retry attempts.
Table 21. SMBUS ERROR RETRY TIMES
DIMM Temperatures from PCH
0x10 bits <4:3>
SMBus Retry Interval
• Read DIMM from PCH, 0xB5 bit 7
If this bit is set to 1 then the SMBus master port will read
the DIMM registers from the SMLINK1 port of the PCH and
store the results in registers 0xA9 to 0xAC. If it is 0 then it
will read DIMM temperatures from SMBus slave devices.
00
01
10
11
1 ms
2 ms
4 ms
8 ms
DIMM Temperatures from Remote Sensors
• DIMM 0/1 from Remote1, 0xB5 bit 5
• DIMM 2/3 from Remote2, 0xB5 bit 6
If the device fails 3 consecutive read attempts then the
PWMx Response bits determine the fan behaviour.
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NCT7491
will be calculated for each temperature and the highest
• If bit 5 of 0x11 is 1 then PWM1 will go to 100% duty
or Max duty. If bit 5 is 0 then the error is ignored.
• If bit 6 of 0x11 is 1 then PWM2 will go to 100% duty
or Max duty. If bit 6 is 0 then the error is ignored.
calculated PWM value will be output. If no temperature
sources are selected then the associated PWM channel
defaults to manual mode.
Registers for assigning zones to PWM1:
• If bit 7 of 0x11 is 1 then PWM3 will go to 100% duty
• Local/Remote1/Remote2 Control, 0x8A bits <2:0>
• PECI Control, 0x8A, bits <6:3>
• SMBus Thermal Slave Control, 0x8B bits <7:0>
• Push Temperature Control, 0x8C bits <3:0>
or Max duty. If bit 7 is 0 then the error is ignored.
Whether the PWM outputs go to 100% or Max duty is
determined by bits <4:2> of register 0x16. See the THERM
ASSERTION section of this document for more details.
Registers for assigning zones to PWM2:
SMBus Master Status Registers
• Local/Remote1/Remote2 Control, 0x8D bits <2:0>
• PECI Control, 0x8D, bits <6:3>
• Bad Block read byte count, 0x81 bit 6
• NACK bits, 0xB6 bits <7:0>
• SMBus Thermal Slave Control, 0x8E bits <7:0>
• PEC error bits, 0xB7 bits <7:0>
• Push Temperature Control, 0x8F bits <3:0>
Registers for assigning zones to PWM3:
• Local/Remote1/Remote2 Control, 0x90 bits <2:0>
• PECI Control, 0x90, bits <6:3>
• SMBus Thermal Slave Control, 0x91 bits <7:0>
• Push Temperature Control, 0x92 bits <3:0>
For example if the user wants to control PWM1 from the
hottest of the CPU temperature, PCH temperature and the
Remote1 sensor then the Control Source registers would be
programmed as:
• SMBus Timeout bits, 0xB8 bits <7:0>
• High/Low Limit exceeded bits, 0xB9 bits <7:0>
• PCH Data Invalid, 0xBA bits <4:0>
• THERM Limit exceeded, 0xBB bits <7:0>
Bad Block Read Count will assert if the byte count returned
by the block read command is insufficient to read the
required temperatures.
NACK bits will assert if a device does not acknowledge its
SMBus address.
PEC error bits will assert if the PEC byte is incorrect.
SMBus Timeout bits will assert if the bus is locked.
• 0x8A <3> = 1
• 0x8A <1> = 1
• 0x8B <0> = 1
(PECI0)
(Remote1)
High/Low Limit bits will assert if the temperature returned
is at or below the programmed low limit value.
(SMBus Device 0, PCH)
PCH Data Invalid bits will assert if the PCH returns
reserved temperature codes
Tmin/Trange Automatic Fan Control
The PWM channels can be put into Tmin/Trange in the
following way:
• Setting bit <0> of register 0x10 to 0 puts PWM1 in
Tmin/Trange mode
• Setting bit <1> of register 0x10 to 0 puts PWM2 in
Tmin/Trange mode
• Setting bit <2> of register 0x10 to 0 puts PWM3 in
Tmin/Trange mode
THERM Limit bits will assert if the returned temperature
is greater than the programmed THERM limit
The status bits ((except THERM status) will hold their
value until the registers are read through the SMBus slave
port. Status bits (except THERM status) can be masked by
setting the corresponding bits in registers 0xBB to 0xBF.
THERM Limit status bits will automatically clear when the
temperature is below the SMBus THERM limit, unless
THERM hysteresis is enabled (setting bit 0 of register 0x11)
in which case the temperature must drop below THERM
limit − Hysteresis.
100%
PWMmax
Automatic Fan Control
There are two automatic fan control methods that can be
selected in the NCT7491. Each PWM channel can be set to
use the Tmin/Trange control method or to use an 8 point
PWM Look−Up Table. In both cases one or more
temperature channels can be assigned to control each PWM
output.
PWMmin
Fan Off or
PWMmin
Assigning Temperature Zones for Automatic Fan Control
These registers allow the temperature zone to be assigned
to a PWM channel by setting the appropriate bit. Any
combination of temperature zones can be assigned to control
any fan. If more than one zone is selected then a PWM value
THERM
Tmin
Trange
Figure 11. PWM Control Curve in Tmin/Trange Mode
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NCT7491
The control loop behaviour in Tmin/Trange mode is
PECI Tmin
determined by the Tmin, PWMmin, Trange and PWMmax
values. Tmin sets the temperature at which the fan turns on
and PWMmin is the PWM value at Tmin. Trange sets the
temperature range over which the PWM output increases
from PWMmin to PWMmax. These settings set the slope of
the curve. Each temperature source has its own associated
Tmin/Trange values. The THERM limit associated with the
temperature channel can override the fan control curve if a
THERM event occurs.
PECI Tmin values must be programmed in the same
format selected for PECI fan control (selected by bit 2 of
register 0x73). If relative mode is selected then Tmin is
programmed in 2’s Complement format. If absolute mode is
selected then Tmin is programmed as an unsigned value. If
Absolute PECI mode is used then the maximum valid Tmin
value is 175°C.
Analog Sensor Tmin
The Tmin value for the analog sensors (Remote1/
Remote2/Local) must be written in the same format as the
measurement registers, i.e. if they are in Offset 64 format
then the Tmin value for these channels must also be written
in Offset 64 format. If they are in 2’s Complement format
then Tmin must be written in the range 0°C to 127°C.
Minimum PWM values:
• PWM1 Minimum Duty, 0x64
• PWM2 Minimum Duty, 0x65
• PWM3 Minimum Duty, 0x66
These set the lowest PWM at which the fan will run. One
Lsb equals 0.39% duty cycle. Minimum PWM values only
apply in Tmin/Trange mode.
SMBus Tmin
The SMBus Tmin value should be programmed as an
unsigned 8−bit value in the range 0°C to 175°C.
Push Tmin
The Push register Tmin value should be programmed as
a value in the range 0°C to 127°C.
Tmin Hysteresis
Hysteresis can be applied to the Tmin temperature to
prevent the fan from turning on and off rapidly around Tmin.
Each temperature has its own hysteresis value that can be
applied. The range of possible values is 0°C to 15°C.
Maximum PWM values:
• PWM1 Maximum Duty, 0x38
• PWM2 Maximum Duty, 0x39
• PWM3 Maximum Duty, 0x3A
These set the maximum duty at which the fans will run.
THERM assertions can be configured to over−ride this to
allow the fans to go to 100% duty on a THERM event. See
the THERM ASSERTION section for more details.
PWM duty cycle registers:
• PWM1 Duty, 0x30
• PWM2 Duty, 0x31
Table 22. HYSTERESIS REGISTERS
Temperature
Remote1
Local
Hystersis
Register 0x6D <7:4>
Register 0x6D <3:0>
Register 0x6E <7:4>
Register 0x6E <3:0>
Register 0xB5 <4:1>
Register 0xEB <3:0>
• PWM3 Duty, 0x32
The current duty cycle calculated by the control loop can
be read in these registers. If the PWM channel is not
associated with a temperature zone then that channel’s duty
cycle register will become writeable (manual mode).
Remote2
PECI
SMBus slave
Push registers
Tmin/Trange values for all Temperature Sources:
• PECI Tmin. 0x3B
• PECI Trange, 0x3C bits <7:4>
• Remote1 Tmin, 0x67
PWM Behaviour below Tmin:
• PWM1 on below Tmin, 0x62 bit 5
• PWM2 on below Tmin, 0x62 bit 6
• PWM3 on below Tmin, 0x62 bit 7
• Remote1 Trange, 0x5F bits <7:4>
• Local Tmin, 0x68
• Local Trange, 0x60 bits <7:4>
• Remote2 Tmin, 0x69
Setting these bits to 1 will cause the associated PWM
output to remain at the minimum PWM value rather than
shut off when the control temperature is below its Tmin
value minus hysteresis. This setting applies to both
Tmin/Trange mode and to Look−Up Table mode.
• Remote2 Trange, 0x61 bits <7:4>
• SMBus slave Tmin, 0xC6
• SMBus slave Trange, 0xC7 bits <3:0>
• Push temperature Tmin, 0xCC
• Push temperature Trange, 0xCD bits <3:0>
Trange Values
The Trange values determine the temperature range over
which the fan control curve will increase from the PWM
minimum value to the PWM maximum value associated
with the PWM output.
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The 4−bit Trange values that can be assigned for each
Setting the PWM Frequency
channel are shown in the following table:
Each PWM output can be set to high frequency PWM
mode or low frequency PWM mode. In high frequency
mode the output will run at 22 kHz. In low frequency mode
the frequency can be selected for each PWM output.
Table 23. TRANGE OPTIONS
Trange Bit Field
0000
Trange Value
2°C
2.5°C
3.33°C
4°C
Setting bit <3> of register 0x5F to 1 enables high frequency
for PWM1
0001
Setting bit <3> of register 0x60 to 1 enables high frequency
for PWM2
0010
0011
Setting bit <3> of register 0x61 to 1 enables high frequency
for PWM3
0100
5°C
0101
6.67°C
8°C
If low frequency is enabled (if bit <3> in 0x5F, 0x60 or 0x61
is 0) then the frequency is set as follows:
0110
0111
10°C
Table 25. LOW FREQUENCY PWM SELECTION
1000
13.33°C
16°C
0x5F, 0x60 or 0x61 bits <2:0>
Frequency
11.0 Hz
14.7 Hz
22.1 Hz
29.4 Hz
35.3 Hz
44.1 Hz
58.8 Hz
88.2 Hz
1001
000
001
010
011
100
101
110
111
1010
20°C
1011
26.67°C
32°C
1100
1101
40°C
1110
53.33°C
80°C
1111
Enabling Enhanced Acoustics on the PWM Outputs:
• PWM1 Max Ramp Rate, 0x62 bits <2:0>
• PWM1 enable acoustics, 0x62 bit 3
Look−Up Table Automatic Fan Control
In this mode the selected PWM output is controlled by an
8−point look−up table, where a temperature and PWM value
is programmed for each point. Each channel has its own
control table. Any combination of temperature sources can
be assigned to control the PWM output. When more than one
channel is assigned to control a PWM output in this mode the
channel that is the hottest will control the output. The
exception to this is if PECI relative temperatures are
assigned to contol a channel. Since PECI relative values are
always negative they cannot be combined with other
channels, since the other channels would always dominate
due to the fact that they are positive values. To allow PECI
readings to be combined with other readings the user can set
bit 2 of register 0x73 (ABS/REL). This will cause the
absolute PECI readings to be used for fan control, rather than
the relative readings.
• If relative PECI readings are assigned for fan control
then the control temperature values for that PWM
channel must be programmed in negative 2’s
complement format (−128°C to 127°C).
• If any temperature source other than relative PECI is
assigned for fan control (including absolute PECI
readings) then the control temperatures for that PWM
channel must be programmed in unsigned format (0°C
to 255°C).
• PWM2 Max Ramp Rate, 0x63 bits <6:4>
• PWM2 enable acoustics, 0x63 bit 7
• PWM3 Max Ramp Rate, 0x63 bits <2:0>
• PWM3 enable acoustics, 0x63 bit 3
These settings allow the user to limit the rate at which the
PWM output changes whenever the fan control loop
calculates a new value. As this prevents instant changes in
PWM the acoustic response of the system is improved.
These settings apply to both Tmin/Trange mode and to
Look−Up Table mode.
Table 24. ENHANCED ACOUSTICS TIMES
Ramp Rate code
Settling time
31.75 sec
15.7 sec
10.5 sec
6.33 sec
4 sec
000
001
010
011
100
101
110
111
2.66 sec
1.28 sec
0.75 sec
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NCT7491
• PWM values are programmed in the range 0x00 to
• Setting bit <1> of register 0x10 to 1 puts PWM2 in
0xFF. The resolution for this register is 1 lsb = 0.392%.
The NCT7491 linearly interpolates between the
programmed points. It is not necessary to program all 8
points. If fewer than 8 points are required then the user
should program from the lowest to the highest required
control temperature and set the unused control temperatures
to the maximum value (0x00 if relative PECI is assigned,
0xFF if the PWM channel is controlled by any other
temperature source).
Look−up Table mode
• Setting bit <2> of register 0x10 to 1 puts PWM3 in
Look−up Table mode
The registers used for setting the control temperatures and
PWMs for each channel are on page 2 of the register map.
To access these registers the user must first set bit 0 of
register 0xFF to 1. This will set the register page to page 2.
When programming the table is complete the user should
clear bit 0 of register 0xFF to zero to return to page 1 of the
register map.
• Setting bit <0> of register 0x10 to 1 puts PWM1 in
Look−up Table mode
Table 26. PWM1 LOOK−UP TABLE VALUES
PWM1 Control Points
Temperature Address
0x00 (0x100)
PWM Address
0x01 (0x101)
0x03 (0x103)
0x05 (0x105)
0x07 (0x107)
0x09 (0x109)
0x0B (0x10B)
0x0D (0x10D)
0x0F (0x10F)
PWM1 Control Point 1
PWM1 Control Point 2
PWM1 Control Point 3
PWM1 Control Point 4
PWM1 Control Point 5
PWM1 Control Point 6
PWM1 Control Point 7
PWM1 Control Point 8
0x02 (0x102)
0x04 (0x104)
0x06 (0x106)
0x08 (0x108)
0x0A (0x10A)
0x0C (0x10C)
0x0E (0x10E)
Table 27. PWM2 LOOK−UP TABLE VALUES
PWM2 Control Points
Temperature Address
0x10 (0x110)
PWM Address
0x11 (0x111)
0x13 (0x113)
0x15 (0x115)
0x17 (0x117)
0x19 (0x119)
0x1B (0x11B)
0x1D (0x11D)
0x1F (0x11F)
PWM2 Control Point 1
PWM2 Control Point 2
0x12 (0x112)
PWM2 Control Point 3
0x14 (0x114)
PWM2 Control Point 4
0x16 (0x116)
PWM2 Control Point 5
0x18 (0x118)
PWM2 Control Point 6
0x1A (0x11A)
0x1C (0x11C)
0x1E (0x11E)
PWM2 Control Point 7
PWM2 Control Point 8
Table 28. PWM3 LOOK−UP TABLE VALUES
PWM3 Control Points
Temperature Address
0x20 (0x120)
0x22 (0x122)
0x24 (0x124)
0x26 (0x126)
0x28 (0x128)
0x2A (0x12A)
0x2C (0x12C)
0x2E (0x12E)
PWM Address
0x21 (0x121)
0x23 (0x123)
0x25 (0x125)
0x27 (0x127)
0x29 (0x129)
0x2B (0x12B)
0x2D (0x12D)
0x2F (0x12F)
PWM3 Control Point 1
PWM3 Control Point 2
PWM3 Control Point 3
PWM3 Control Point 4
PWM3 Control Point 5
PWM3 Control Point 6
PWM3 Control Point 7
PWM3 Control Point 8
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NCT7491
Fan Override Settings
5
100%
There are bits in the NCT7491 that allow the PWM
outputs to be overdriven so that the outputs go to maximum
speed (as programmed in the maximum PWM registers), to
go to full speed (100% duty) or to be shut off. These bits will
override all other fan control settings.
• Setting bit 1 of register 0x11 to 1 runs the fans at the
maximum programmed PWM duty cycle
4
3
PWM
2
1
• Setting bit 3 of register 0x40 to 1 runs the fans at 100%
duty cycle. This bit has precedence over all others.
• Setting bit 0 of register 0x87 to 1 turns off PWM1
• Setting bit 1 of register 0x87 to 1 turns off PWM2
• Setting bit 2 of register 0x87 to 1 turns off PWM3
3
4 5
6,7,8
1
2
0°C
THERM Override
255°C
Temperature
Setting bit 5 of register 0x40 will allow assertions on any
pin configured as a THERM pin to drive the fans to 100%
duty cycle or Max PWM, deending on bits <4:2> of register
0x16. This will override all other fan settings. This allows an
external device to bypass the register settings of the
NCT7491 for fail safe operation.
Figure 12.
Figure 12 shows a typical look−up table curve. The
temperatures are programmed as unsigned data. In this
example 5 of the 8 control points are used and the remaining
3 are set to the maximum value of 255°C. This curve applies
if relative PECI values are not assigned to control the PWM
channel.
Fan Drive
The NCT7491 uses pulse width modulation (PWM) to
control fan speed. This relies on varying the duty cycle (or
on/off ratio) of a square wave applied to the fan to vary the
fan speed. The external circuitry required to drive a fan using
PWM control is extremely simple. For 4−wire fans, the
PWM drive may need only a pullup resistor. In many cases
the 4−wire fan PWM input has an internal pullup resistor.
The NCT7491 PWM frequency can be set to a selection of
low frequencies or a single high PWM frequency. The low
frequency options are used for 3−wire fans, while the high
frequency option is usually used with 4−wire fans. For
3−wire fans, a single N−channel MOSFET is the only drive
device required. The specifications of the MOSFET depend
on the maximum current required by the fan being driven
and the input capacitance of the FET. Because a 10 k (or
greater) resistor must be used as a PWM pullup, an FET with
large input capacitance can cause the PWM output to
become distorted and adversely affect the fan control range.
This is a requirement only when using high frequency PWM
mode. Typical notebook fans draw a nominal 170 mA,
therefore, SOT devices can be used where board space is a
concern. In desktops, fans typically draw 250 mA to 300 mA
each. If several fans are driven in parallel from a single
PWM output or drive larger server fans, the MOSFET must
handle the higher current requirements. The only other
stipulation is that the MOSFET should have a gate voltage
drive, VGS < 3.3 V, for direct interfacing to the PWM output
pin.
100%
5
4
3
PWM
2
1
3
4 5
6,7,8
1
2
0°C
−128°C
Temperature
Figure 13.
Figure 13 shows a typical look−up table curve that applies
when relative PECI values are assigned to control the PWM
channel. The temperatures are programmed as negative 2’s
complement values. In this example 5 of the 8 control points
are used and the remaining 3 are set to the maximum value
of 0°C, as this is the maximum value for relative PECI
values.
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NCT7491
Figure 14. Driving a 3−Wire Fan Using an N−Channel MOSFET
Figure 14 uses a 10 k pullup resistor for the TACH signal.
these devices are inexpensive, they tend to have much lower
current handling capabilities and higher on resistance than
MOSFETs. When choosing a transistor, care should be taken
to ensure that it meets the fan’s current requirements. Ensure
that the base resistor is chosen so that the transistor is
saturated when the fan is powered on.
This assumes that the TACH signal is an open−collector
from the fan. In all cases, the TACH signal from the fan must
be kept below 3.6 V maximum to prevent damaging the
NCT7491.
Figure 15 shows a fan drive circuit using an NPN
transistor such as a general purpose MMBT2222. While
Figure 15. Driving a 3−Wire Fan Using an NPN Transistor
Because the fan drive circuitry in 4−wire fans is not
switched on or off, as with previous PWM driven/powered
fans, the internal drive circuit is always on and uses the
PWM input as a signal instead of a power supply. This
enables the internal fan drive circuit to perform better than
3−wire fans, especially for high frequency applications.
Figure 16 shows a typical drive circuit for 4−wire fans.
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NCT7491
Figure 16. Driving a 4−Wire Fan
Driving Two Fans from PWM3
The NCT7491 has four TACH inputs available for fan
speed measurement, but only three PWM drive outputs. If a
fourth fan is being used in the system, it should be driven
from the PWM3 output in parallel with the third fan.
Figure 17 shows how to drive two fans in parallel using a
MOSFET. Because the MOSFET can handle up to 3.5 A, it
is simply a matter of connecting another fan directly in
parallel with the first. Care should be taken in designing
drive circuits with transistors and FETs to ensure the PWM
outputs are not required to source current, and that they sink
less than the 5 mA maximum current specified in the data
sheet.
Figure 17. Interfacing Two Fans in Parallel to the PWM3 Output Using a Single N−Channel MOSFET
Driving up to Three Fans from PWM3
Synchronization is not required in high frequency mode
when used with 4−wire fans.
Setting bit 4 of register 0x62 (SYNC) to 1 synchronizes
TACH2, TACH3, and TACH4 to PWM3.
TACH measurements for fans are synchronized to
particular PWM channels; for example, TACH1 is
synchronized to PWM1. TACH3 and TACH4 are both
synchronized to PWM3, so PWM3 can drive two fans.
Alternatively, PWM3 can be programmed to synchronize
TACH2, TACH3, and TACH4 to the PWM3 output. This
allows PWM3 to drive two or three fans. In this case, the
drive circuitry looks the same, as shown in Figure 17. The
SYNC bit in Register 0x62 enables this function.
TACH Inputs
Pins 9, 11, 12 and 14 on the QSOP package or pins 6, 8,
9 and 11 on the QFN package (when configured as TACH
inputs) are high impedance inputs intended for fan speed
measurement. Signal conditioning in the NCT7491
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NCT7491
accommodates the slow rise and fall times typical of fan
clamping must be included to keep inputs within an
acceptable range. Figure 18 to Figure 20 show circuits for
the most common fan TACH outputs. If the fan TACH
output has a resistive pullup to VCC, it can be connected
directly to the fan input, as shown in Figure 18.
tachometer outputs. The maximum input signal range is 0 V
to 3.6 V, even though VCC is 3.3 V. In the event that these
inputs are supplied from fan outputs that exceed 0 V to 3.6 V,
either resistive attenuation of the fan signal or diode
Figure 18. Fan with TACH Pullup to VCC
If the fan output has a resistive pullup to 12 V, or other
voltage greater than 3.6 V, the fan output can be clamped
with a zener diode, as shown in Figure 19. The zener diode
voltage should be chosen so that it is greater than VIH of the
TACH input but less than 3.6 V, allowing for the voltage
tolerance of the zener. A value of between 3.0 V and 3.6 V
is suitable.
Figure 19. Fan with TACH Pullup to Voltage > 3.6 V, for Example, 12 V Clamped with Zener Diode
If the fan has a strong pullup (less than 1 k_) to 12 V or a totem−pole output, a series resistor can be added to limit the zener
current, as shown in Figure 20.
Figure 20. Fan with Strong TACH Pullup to >VCC or Totem−Pole Output, Clamped with Zener Diode and Resistor
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NCT7491
TACH Measurement Overview
the fan TACH output (see Figure 21) so the accumulated
count is actually proportional to the fan tachometer period
and inversely proportional to the fan speed. N, the number
of pulses counted, is determined by the settings of the TACH
pulses per revolution register (0x7B). This register contains
two bits for each fan, allowing one, two (default), three, or
four TACH pulses to be counted.
The fan counter does not count the fan TACH output
pulses directly because the fan speed could be less than 1000
RPM, and it takes several seconds to accumulate a
reasonably large and accurate count. Instead, the period of
the fan revolution is measured by gating an on−chip 78 kHz
oscillator into the input of a 16−bit counter for N periods of
Figure 21. Fan Speed Measurement
Fan Speed Measurement Registers
Fan TACH Limit Registers
The fan tachometer registers are 16−bit values consisting
of a 2−byte read from the NCT7491.
The fan TACH limit registers are 16−bit values consisting
of two bytes.
• Register 0x28, TACH1 Low Byte
• Register 0x29, TACH1 High Byte
• Register 0x2A, TACH2 Low Byte
• Register 0x2B, TACH2 High Byte
• Register 0x2C, TACH3 Low Byte
• Register 0x2D, TACH3 High Byte
• Register 0x2E, TACH4 Low Byte
• Register 0x2F, TACH4 High Byte
• Register 0x54, TACH1 Minimum Low Byte = 0xFF
default
• Register 0x55, TACH1 Minimum High Byte = 0xFF
default
• Register 0x56, TACH2 Minimum Low Byte = 0xFF
default
• Register 0x57, TACH2 Minimum High Byte = 0xFF
default
• Register 0x58, TACH3 Minimum Low Byte = 0xFF
default
Reading Fan Speed from the NCT7491
• Register 0x59, TACH3 Minimum High Byte = 0xFF
The measurement of fan speeds involves a 2−register read
for each measurement. The low byte should be read first.
This causes the high byte to be frozen until both high and low
byte registers have been read, preventing erroneous TACH
readings. The fan tachometer reading registers report back
the number of 12.82 us period clocks (78 kHz oscillator)
gated to the fan speed counter, from the rising edge of the
first fan TACH pulse to the rising edge of the third fan TACH
pulse (assuming two pulses per revolution are being
counted). Because the device is essentially measuring the
fan TACH period, the higher the count value, the slower the
fan is actually running. A 16−bit fan tachometer reading of
0xFFFF indicates that either the fan has stalled or is running
very slowly (<100 RPM).
default
• Register 0x5A, TACH4 Minimum Low Byte = 0xFF
default
• Register 0x5B, TACH4 Minimum High Byte = 0xFF
default
Fan Speed Measurement Rate
The fan TACH readings are normally updated once every
second. When set, the FAST bit (Bit 3) of Configuration
Register 3 (0x78), updates the fan TACH readings every
250 ms.
DC Bits
If any of the fans are not being driven by a PWM channel
but are powered directly from 5.0 V or 12 V, their associated
dc bit in Configuration Register 3 (0x78) should be set. This
Because the actual fan TACH period is being measured,
falling below a fan TACH limit by 1 sets the appropriate
status bit and can be used to generate an SMBALERT
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NCT7491
allows TACH readings to be taken on a continuous basis for
TACH Pulses per Revolution Register 0x7B
• Bits [1:0], FAN1 default = 2 pulses per revolution
• Bits [3:2], FAN2 default = 2 pulses per revolution
• Bits [5:4], FAN3 default = 2 pulses per revolution
• Bits [7:6], FAN4 default = 2 pulses per revolution
• 00 = 1 pulse per revolution
fans connected directly to a dc source. For 4−wire fans, once
high frequency mode is enabled, the dc bits do not need to
be set because this is automatically done internally.
If any tach channels are not connected then the associated
DC bit should be set for that fan.
Calculating Fan Speed From Register Values
• 01 = 2 pulses per revolution
Assuming a fan with a two pulses per revolution, and with
the NCT7491 programmed to measure two pulses per
revolution, fan speed is calculated by Fan Speed (RPM) =
(78,000 x 60)/Fan TACH Reading where Fan TACH
Reading is the 16−bit fan tachometer reading.
• 10 = 3 pulses per revolution
• 11 = 4 pulses per revolution
Fan Spin−Up
The NCT7491 has a unique fan spin−up function. It spins
the fan at 100% PWM duty cycle until two TACH pulses are
detected on the TACH input. When two TACH pulses have
been detected, the PWM duty cycle goes to the expected
running value, for example, 33%. The advantage of this is
that fans have different spin−up characteristics and take
different times to overcome inertia. The NCT7491 runs the
fans just fast enough to overcome inertia and is quieter on
spin−up than fans programmed to spin up for a given
spin−up time.
Example:
TACH1 High Byte (Register 0x29) = 0x17
TACH1 Low Byte (Register 0x28) = 0xFF
What is Fan 1 speed in RPM?
Fan 1 TACH Reading = 0x17FF = 6143 (decimal)
RPM = (f x 60)/Fan 1 TACH Reading
RPM = (78000 x 60)/6143
Fan Speed = 762 RPM
Fan Pulses per Revolution
Fan Startup Timeout
Different fan models can output one, two, three, or four
TACH pulses per revolution. Once the number of fan TACH
pulses has been determined, it can be programmed into the
TACH pulses per revolution register (0x7B) for each fan.
Alternatively, this register can be used to determine the
number or pulses per revolution output by a given fan. By
plotting fan speed measurements at 100% speed with
different pulses per revolution setting, the smoothest graph
with the lowest ripple determines the correct pulses per
revolution value.
To prevent the generation of false interrupts as a fan spins
up, because the fan is below running speed, the NCT7491
includes a fan startup timeout function. During this time, the
NCT7491 looks for two TACH pulses. If two TACH pulses
are not detected, an interrupt is generated. Fan startup
timeout can be disabled by setting Bit 3 (FSPDIS) of
Configuration Register 7 (0x11).
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NCT7491
THERM Assertion
• If Offset64 mode is enabled then
Pins 14, 19 and 22 on the QSOP package, or pins 11, 16
and 19 on the QFN package can be configured as THERM
I/O pins. These are open−drain active low pins used to signal
that a critical temperature limit has been exceeded. If a
temperature measurement exceeds its associated THERM
limit (or Tcontrol limit for PECI) then the THERM pin will
assert low. THERM assertion can be enabled or disabled for
each thermal measurement channel. PWM outputs can be
configured to respond to THERM assertions. By default
THERM assertion will cause the PWM outputs to go to
100% duty cycle for fail safe cooling. This can be
individually disabled for each PWM output. THERM
assertion behavior can be modified so that the outputs do not
immediately go to 100% when THERM asserts. If this
function is enabled then an associated temperature step
register is used to increase the PWM duty in steps. For
example, if the step register is set to 4 degrees then the PWM
output will go to PWMStep1 at the THERM limit, to
PWMStep2 at THERM+4 and 100% at THERM+2x4,
where PWMStep1 and PWMStep2 are programmable
PWM levels.
Remote1/Local/Remote2 THERM limits should be
programmed in that format. Otherwise those limits
should be programmed as 2’s complement values.
• If PECI Absolute mode is enabled than PECI Tcontrol
limits should be programmed as unsigned values,
otherwise they should be programmed as 2’s
complement values.
• SMBus THERM limit should be programmed as an
unsigned value.
• Push THERM limit should be programmed as a 2’s
complement value.
THERM Status Bits
• PECI Tcontrol status bits = 0x89 <3:0>
• Remote1 THERM status bit = 0x89 <4>
• Local THERM status bit = 0x89 <5>
• Remote2 THERM status bit = 0x89 <6>
• SMBus slave THERM status bits = 0xBB <7:0>
• Push THERM status bits = 0x7E <7:4>
Enabling THERM/Tcontrol Assertions for the
Temperature Channels
THERM Pin Configuration
Configuring Pin 14 (QSOP), Pin 11 (QFN) as a THERM pin:
• Set 0x7C bit 4 to 1 to enable PECI T
pin
CONTROL
Setting bits <1:0> of register 0x7D to <01> sets pin 14 on the
QSOP package or pin 11 on the QFN package as a THERM
pin.
assertions
• Set 0x7C bit 5 to 1 to enable Remote1 THERM pin
assertions,
Configuring Pin 19 (QSOP), Pin 16 (QFN) as a THERM pin:
• Set 0x7C bit 6 to 1 to enable Local THERM pin
Setting bits <3:2> of register 0x7C to <01> sets pin 19 on the
QSOP package or pin 16 on the QFN package as a THERM
pin.
assertions,
• Set 0x7C bit 7 to 1 to enable Remote2 THERM pin
assertions,
Configuring Pin 22 (QSOP), Pin 19 (QFN) as a THERM pin:
• Set 0x16 bit 5 to 1 to enable Push temperature THERM
pin assertions,
Setting bit 1 of register 0x78 to 1 enables pin 22 on the QSOP
package or pin 19 on the QFN package as a THERM pin.
• Set 0x16 bit 6 to 1 to enable SMBus slave THERM pin
assertions
THERM/Tcontrol Limit Registers
• Remote1 THERM Limit, 0x6A
• Local THERM Limit, 0x6B
• Remote2 THERM Limit, 0x6C
• PECI0 Tcontrol Limit, 0x3D
• PECI1 Tcontrol Limit, 0x08
• PECI2 Tcontrol Limit, 0x09
• PECI3 Tcontrol Limit, 0x0A
PECI T
enable bit applies to all PECI channels
CONTROL
Push temperature THERM enable applies to all Push
channels
SMBus slave enable bit applies to all SMBus channels
The user should also ensure that the THERM Disable bit,
0x7D <2>, is 0. This is the THERM disable bit and when set
to 1 will disable all THERM pin assertions.
Enabling the PWM Response to THERM Assertions
• PWM1 responds to THERM, 0x17 bit 0
• PWM2 responds to THERM, 0x17 bit 1
• SMBus Device THERM Limit, 0xC3 (applies to all
SMBus devices)
• Push temperature THERM Limit, 0xD0 (applies to all
• PWM3 responds to THERM, 0x17 bit 2
Push channels)
If these bits are set to 1 then the associated PWM output
will be affected by a THERM assertion. There are 3 possible
responses: go to 100%, go to Maximum PWM or implement
the THERM Stepping function.
If any temperature channel exceeds its associated
THERM limit then a status bit will be set to indicate the
condition. If that channel is enabled for pin assertions and a
THERM pin has been configured then the pin will assert. If
the temperature value goes below its THERM limit then the
status bit will automatically clear and the pin will de−assert.
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NCT7491
Setting the PWM Level for THERM Events
• PWM1 Max/Full, 0x16, bit 2
Setting the PWM Levels for THERM Stepping
• PWMStep1 Value, 0x14
• PWMStep2 Value, 0x15
• PWM2 Max/Full, 0x16, bit 3
PWMStep1 sets the PWM level that is output when a
temperature exceeds its THERM limit (and Stepping is
enabled). PWMStep2 sets the PWM level if the temperature
exceeds THERM Limit + Step, where Step is the
programmed step size for the temperature channel.
PWMStep1 and PWMStep2 are absolute PWM values
and have a resolution of 1 lsb = 0.392%.
• PWM3 Max/Full, 0x16, bit 4
If these bits are set to 1 then the fans will go to 100% on
THERM assertion. If they are 0 then they will go to the
Maximum PWM value.
These bits are ignored if the THERM stepping function is
enabled.
NOTE: If stepping is enabled for a temperature channel
controlling a PWM output, then that PWM
output will only respond to THERM events
generated by its own temperature control
sources and will not respond to THERM events
from other temperature sources.
100%
PWMStep2
PWMStep1
THERM Timer
PWM
The NCT7491 has an internal timer to measure THERM
assertion time. For example, the THERM input can be
connected to the PROCHOT output of a CPU to measure
system performance. The THERM input can also be
connected to the output of a trip point temperature sensor.
The timer is started on the assertion of the NCT7491
THERM input and stopped when THERM is deasserted.
The timer counts THERM times cumulatively, that is, the
timer resumes counting on the next THERM assertion. The
THERM timer continues to accumulate THERM assertion
times until the timer is read (it is cleared on read), or until it
reaches full scale. If the counter reaches full scale, it stops
at that reading until cleared.
The 8−bit THERM timer value register (0x79) is designed
so that Bit 0 is set to 1 on the first THERM assertion. Once
the cumulative THERM assertion time has exceeded 45.52
ms, Bit 1 of the THERM timer is set and Bit 0 now becomes
the LSB of the timer with a resolution of 22.76 ms (see
Figure 23).
Step Step
Tmin
THERM
Temperature
Figure 22. THERM Stepping Function
THERM Stepping Function
If the THERM Stepping function is enabled then the
associated PWM output goes to PWMStep1 when the
temperature is higher than THERM. The PWM output goes
to PWMStep2 when the temperature is higher than
THERM+Step and goes to 100% if the temperature reaches
THERM+2xStep. THERM stepping does not apply to PWM
channels in look−up table mode.
THERM Stepping is enabled by writing a value greater
than 0°C to the THERM Step Size registers
After a pin has been configured as a THERM pin the timer
function can be enabled on the pin using bits <1:0> of
register 0x16:
• <00> = Timer disabled
• <01> = Timer enabled on pin 14 (QSOP), pin 11 (QFN)
• <10> = Timer enabled on pin 19 (QSOP), pin 16 (QFN)
• <11> = Timer enabled on pin 22 (QSOP), pin 19 (QFN)
Setting the THERM Step Size
• SMBus slave THERM Step, 0x18, bits <3:0>
• PECI THERM Step, 0x18 bits <7:4>
• Remote1/Local/Remote2 THERM Step, 0x19 bits <3:0>
• Push temperature THERM Step, 0x19 bits <7:4>
The range of temperature values that can be programmed
for the Step size is 0 to 15°C. If set to 0 then the stepping
function is disabled.
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33
NCT7491
Enabling Pins as SMBALERT Pins
• Setting bit 0 of register 0x78 sets pin 10 on the QSOP
package, or pin 7 on the QFN package as an
SMBALERT pin.
• Setting bits <1:0> of register 0x7D to <10> sets pin 14
on the QSOP package or pin 11 on the QFN package as
an SMBALERT pin.
• Setting bits <3:2> of register 0x7C to <00> sets pin 19
on the QSOP package or pin 16 on the QFN package as
an SMBALERT pin.
NCT7491 Status Bits
When a status bit is set and the SMBALERT output asserts
it may be necessary to read the status registers to determine
the source of the assertion. To minimize to number of
register reads required the NCT7491 uses Out Of Limit bits
(OOL bits) to indicate in which registers an assertion has
occurred.
By first reading Status OOL register address 0x12 it can
be determined which other status registers are active. Once
set, a status bit will remain set until the register that it is
contained in is read over the SMBus interface, even if the
fault that caused the assertion is no longer present.
Figure 23. THERM Timer
THERM Timer Limit
The THERM Timer limit register can be used to assert an
SMBALERT output when the timer measurement exceeds
the programmed limit value. If the value N is programmed
to the limit register then the limit time will be (N + 1) x 22.76
ms.
OOL register 0x12 Definitions:
• Bit 0 of 0x12 = 1 indicates an assertion in register 0x41
(Analog temperature and Voltage limit errors)
• Bit 1 of 0x12 = 1 indicates an assertion in register 0x7E
(Push register limit errors)
• Bit 2 of 0x12 = 1 indicates an assertion in register 0xB6
(SMBus Master NACK errors)
• Bit 3 of 0x12 = 1 indicates an assertion in register 0xB7
(SMBus Master PEC errors)
SMBALERT Functions
All of the measured temperatures, voltages and fan speeds
have associated limit registers to detect when an out of limit
condition occurs on any channel. Each of these channels has
an associated status bit that can be read over the SMBus to
determine the limit. There are also status bits to indicate the
success or failure of various functions, such as the PECI
interface or the SMBus Master Port interface. If a pin is
configured as an SMBALERT pin then any of the status bits
can assert the pin when they are set by the NCT7491. Most
of the status bits can be masked, allowing the user to prevent
assertion of the SMBALERT pins by functions that are not
required in an application. Descriptions of the limit registers
for each temperature, voltage or fan channel are described
in their relevant sections of this document.
• Bit 4 of 0x12 = 1 indicates an assertion in register 0xB8
(SMBus Master Timeout errors)
• Bit 5 of 0x12 = 1 indicates an assertion in register 0xB9
(SMBus Master limit errors)
• Bit 6 of 0x12 = 1 indicates an assertion in register
0xBA (SMBus Master Data Invalid errors)
• Bit 7 of 0x12 = 1 indicates an assertion in register 0x89
(Tcontrol/THERM assertions). This bit relates to
THERM function and does not affect the SMBALERT
pins.
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34
NCT7491
List of Status Registers
the nominal input voltage, and so has adequate headroom to
cope with overvoltages.
The complete list of status registers is given below along
with their associated mask registers. The definitions for the
status bits for each of the registers can be found in the
register tables at the end of this document. OOL bits in any
register do not require to be masked as they do not assert the
SMBALERT pin.
Voltage Input Circuitry
The internal structure for the analog inputs is shown in
Figure 24. The input circuit consists of an input protection
diode, an attenuator, plus a capacitor to form a first−order
low−pass filter that gives input immunity to high frequency
noise. The attenuators can be disabled for the voltage
channels, except for the Vcc channel.
Table 29. STATUS REGISTERS
Status
Register
Address
Mask
Register
Address
Status Bits
215.7 k
12 V
Indicates status assertions in re-
gisters 0x41, 0x7E, 0xB6, 0xB7,
0xB8, 0xB9, 0xBA and 0x89.
0x12
Not
applicable
2.6 pF
30.2 k
85.9 k
5 V
Voltage & Analog temperature
out of limit bits. OOL bit for re-
gister 0x42.
0x41
0x74
2.6 pF
2.6 pF
2.6 pF
36.6 k
Voltage, Fans, Diode Faults.
OOL bit for register 0x43.
0x42
0x43
0x75
0x82
49.4 k
2.5 V
Vcc
PECI0 out of limit, PECI COMM/
DATA error, THERM assertion,
DATA error code. OOL bit for re-
gister 0x81.
74 k
Mux
66.7 k
55.8 k
PECI completion code error,
THERM timer error, Generic
COMM error, PECI1−3 out of lim-
0x81
0x83
it bits, PCH byte count error, V
out of limit bit.
TT
41.1 k
82.3 k
Vccp
2.6 pF
2.6 pF
Push register out of limit bits
SMBus Master NACK errors
SMBus Master PEC errors
SMBus Master Timeout errors
SMBus Master out of limit bits
0x7E
0xB6
0xB7
0xB8
0xB9
0xBA
0x7F
0xBC
0xBD
0xBE
0xBF
0xC0
13.7 k
109.7 k
V
TT
Figure 24. Voltage Input Structures
SMBus Master Data Invalid errors
Voltage Measurement Registers
Voltage Monitoring
The NCT7491 has 5 external voltage measurement
channels. It can also measure its own supply voltage, V
The NCT7491 can measure 5 V, 12 V, and 2.5 V supplies,
and the processor core voltage V (0 V to 3 V input). The
2.5 V input can be used to monitor a chipset supply voltage
in computer systems. The V supply voltage measurement
• Reg. 0x1E, V Reading = 0x00 default
TT
• Reg. 0x20, 2.5 V Reading = 0x00 default
.
CC
• Reg. 0x21, V
Reading = 0x00 default
CCP
• Reg. 0x22, V Reading = 0x00 default
CC
CCP
• Reg. 0x23, 5 V Reading = 0x00 default
• Reg. 0x24, 12 V Reading = 0x00 default
CC
is carried out through the V pin. The PECI V voltage
CC
TT
Extended Resolution Registers
is also measured and is the dedicated reference voltage for
the PECI circuitry.
Voltage measurements can be made with higher accuracy
using the extended resolution registers (0x1F, 0x76 and
0x77). Whenever the extended resolution registers are read,
the corresponding data in the voltage measurement registers
(0x1E, 0x20 to 0x24) is locked until their data is read. That
is, if extended resolution is required, the extended resolution
register must be read first immediately followed by
the appropriate voltage measurement register.
Analog−to−Digital Converter
All analog inputs are multiplexed into the on−chip,
successive− approximation, analog−to−digital converter.
This has a resolution of 10 bits. The basic input range is 0 V
to 2 V, but the inputs have built−in attenuators to allow
measurement of 2.5 V, 3.3 V, 5 V, 12 V, and the processor
core voltage V
without any external components. To
CCP
allow the tolerance of these supply voltages, the ADC
produces an output of 3/4 full scale (768 dec or 300 hex) for
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35
NCT7491
Voltage Measurement Selection
Additional ADC Functions for Voltage Measurements
A number of other functions are available on the
NCT7491 to offer the system designer increased flexibility.
The functions described below are enabled by setting the
appropriate bit in configuration register 2 (0x73).
The user can select which voltage channels to include in
the monitoring loop. By only including the channels that are
required the loop monitoring time can be reduced.
• Setting <2> of register 0x11 includes the V channel
TT
in the monitoring loop.
Turn−Off Voltage Averaging
• Setting <3> of register 0x13 includes the 12V channel
in the monitoring loop.
The averager length that is applied to the temperature
readings is also applied to the voltage readings. The averager
length is programmable as 4, 8, 16 or 32 samples. These
values can be selected in register 0x40 bits <7:6>.
When faster conversions are needed, setting Bit 3 of
Configuration Register 2 (Reg. 0x73) turns voltage
averaging off. This gives a faster reading, but the reading
can be noisier. The default round−robin cycle time takes
TBD ms.
• Setting <4> of register 0x13 includes the 5 V channel in
the monitoring loop.
• Setting <5> of register 0x13 includes the Vccp channel
in the monitoring loop.
• Setting <6> of register 0x13 includes the 2.5 V channel
in the monitoring loop.
• Setting <7> of register 0x13 includes the Vcc channel
in the monitoring loop.
Bypass Individual Voltage Input Attenuators
Bits <7:3> of Configuration Register 4 (0x7D) can be
used to bypass individual voltage channel attenuators.
Voltage Measurement Resolution
The NCT7491 uses a reference voltage of 2 V. The ADC
is 10−bit giving a resolution of 1.953 mV per lsb. This is the
resolution that applies when the attenuators are disabled.
With attenuators enabled the resolution for each channel is
as follows:
Table 30. BYPASSING VOLTAGE ATTENUATORS
Configuration Register 4 (0x7D)
Bit
3
Channel Attenuated
Bypass V attenuator
• 12 V resolution = 15.92 mV per lsb
• 5 V resolution = 6.54 mV per lsb
• 2.5 V resolution = 3.26 mV per lsb
• Vccp resolution = 2.93 mV per lsb
• Vcc resolution = 4.29 mV per lsb
TT
4
Bypass 2.5 V attenuator
5
Bypass V
attenuator
CCP
6
Bypass 5 V attenuator
Bypass 12 V attenuator
7
• V resolution = 2.2 mV per lsb
TT
The input range of the ADC without the attenuators is 0 V
to 2 V.
Voltage Limit Registers
Associated with each voltage measurement channel is a
high and low limit register. Exceeding the programmed high
or low limit causes the appropriate status bit to be set.
Exceeding either limit can also generate SMBALERT
interrupts.
GPIO Functions
There are up to 3 pins that can be configured as open−drain
general purpose digital I/O pins. These are pins 5 (GPIO1),
6 (GPIO2) and 19 (GPIO3) on the QSOP package and pins
2 (GPIO1), 3 (GPIO2) and 16 (GPIO3) on the QFN package.
GPIO1 and GPIO2 are shared with the SMBus Master Port
pins SCL_M and SDA_M. GPIO3 is shared with THERM
and SMBALERT functions.
• Reg. 0x84, V Low Limit
TT
• Reg. 0x86, V High Limit
TT
• Reg. 0x44, 2.5 V Low Limit
• Reg. 0x45, 2.5 V High Limit
There are 2 bits that must be programmed to enable the
GPIO1 and GPIO2 functions:
• Reg. 0x46, V
• Reg. 0x47, V
Low Limit
High Limit
CCP
• Setting bit 1 of register 0x80 to 1 enables GPIO1 and
CCP
GPIO2
• Reg. 0x48, V Low Limit
CC
• Clearing bit 0 of register 0xB5 to 0 disables the SMBus
Master Port. This bit has priority over the GPIO enable
bit so must be cleared for GPIOs to function.
• Reg. 0x49, V High Limit
CC
• Reg. 0x4A, 5 V Low Limit
• Reg. 0x4B, 5 V High Limit
• Reg. 0x4C, 12 V Low Limit
• Reg. 0x4D, 12 V High Limit
GPIO3 is enabled by setting bits <3:2> of register 0x7C to
<10>.
Each GPIO pin has associated direction, polarity and data
bits.
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36
NCT7491
GPIO1
Setting bit 6 of register 0x10 enables the Vccp Low
function. In this mode, if the Vccp voltage falls below the
value in the Vccp Low Limit register (0x46) then the Vccp
status bit is set, the THERM timer function is disabled, PECI
errors are cleared, SMBus Master errors are cleared and all
PWM outputs shut down. When the Vccp voltage increases
above the Vccp Low Limit then any of the above functions
that were previously enabled will become active again.
• Bit 7 of register 0x80 sets GPIO1 direction. 1=Input,
0=Output
• Bit 5 of register 0x80 sets GPIO1 polarity. 1=active
high, 0=active low
• Bit 3 of register 0x80 is GPIO1 data. If GPIO1 is an
input this bit shows the pin state. If it is an output then
this bit sets the output state.
XNOR Tree Test Mode
GPIO2
The NCT7491 includes an XNOR tree test mode. This
mode is useful for in−circuit test equipment at board−level
testing. By applying stimulus to the pins included in the
XNOR tree, it is possible to detect opens, or shorts, on the
system board.
The XNOR tree test is invoked by setting Bit 0 (XEN) of
the XNOR Tree Test Enable register (Register 0x6F).
Figure 25 shows the signals that are exercised in the XNOR
tree test mode.
• Bit 6 of register 0x80 sets GPIO2 direction. 1=Input,
0=Output
• Bit 4 of register 0x80 sets GPIO2 polarity. 1=active
high, 0=active low
• Bit 2 of register 0x80 is GPIO2 data. If GPIO2 is an
input this bit shows the pin state. If it is an output then
this bit sets the output state.
GPIO3
• Bit 7 of register 0x85 sets GPIO3 direction. 1=Input,
0=Output
PWM2
PWM3
• Bit 6 of register 0x85 sets GPIO3 polarity. 1=active
high, 0=active low
• Bit 5 of register 0x85 is GPIO3 data. If GPIO3 is an
input this bit shows the pin state. If it is an output then
this bit sets the output state.
When writing to a GPIO pin that is configured as an output
the polarity must be taken into account. For example, if the
pin is set as active low then writing a 1 to the data bit will pull
the GPIO pin low.
TACH1
TACH2
TACH3
When GPIOs are configured as inputs the data bit always
shows the actual pin state.
VCCP Low Detection
PWM1/XTO
TACH4
If the processor core voltage is being monitored on the
Vccp channel and the NCT7491 is run from the auxiliary
rail, then the user can enable a function to suspend various
functions in the NCT7491 when the core voltage falls below
a programmable threshold.
Figure 25. XNOR Tree Test
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37
NCT7491
Table 31. REGISTER TABLES
Address R/W
Description
PECI0 Address
PECI1 Address
PECI2 Address
PECI3 Address
PECI0_Abs
Bit 7
Bit 6
Bit 5
Bit 4
Bit 3
Bit 2
Bit 1
Bit 0
0x00
0x01
0x02
0x03
0x04
0x05
0x06
0x07
0x08
0x09
0x0A
0x0B
0x0C
0x0D
0x0E
0x0F
0x10
R/W
R/W
R/W
R/W
R
7
6
5
4
3
2
1
0
7
6
5
4
3
2
1
0
7
6
5
4
3
2
1
0
7
6
5
4
3
2
1
0
7
6
5
4
3
2
1
0
R
PECI1_Abs
7
6
5
4
3
2
1
0
R
PECI2_Abs
7
6
5
4
3
2
1
0
R
PECI3_Abs
7
6
5
4
3
2
1
0
R/W
R/W
R/W
R
PECI1 Tcontrol
PECI2 Tcontrol
PECI3 Tcontrol
PECI0 Tjmax
PECI1 Tjmax
PECI2 Tjmax
PECI3 Tjmax
PECI Config 4
Config. 6
7
6
5
4
3
2
1
0
7
6
5
4
3
2
1
0
7
6
5
4
3
2
1
0
7
6
5
4
3
2
1
0
R
7
6
5
4
3
2
1
0
R
7
7
6
6
5
5
4
3
2
2
1
1
0
0
R
4
3
R/W
R/W
DM3CPU
DM3CPU
DM2CPU
IFT
DM2CPU
SMBRT1
DM1CPU
SMBRT0
DM1CPU
DM0CPU
DM0CPU
V
Low
PWM3
Mode
PWM2
Mode
PWM1
Mode
CCP
0x11
0x12
0x13
0x14
0x15
0x16
R/W
R
Config. 7
Interrupt Status 6
Config. 8
SMBFS3
SMBFS2
SMBFS1
TODIS
FSPDIS
VTT
OOL5
Rem2
2
FSPD
OOL4
Rem1
1
THERMHys
OOL10
OOL9
2.5V
6
OOL8
Vccp
5
OOL7
OOL6
12V
3
OOL0
Local
0
Vcc
7
5V
4
R/W
R/W
R/W
PWMStep1
PWMStep2
7
6
5
4
3
2
1
0
THERM Config1
SMBus
THERM
Push
THERM
Max/Full 3 Max/Full 2 Max/Full 1
TMRP1
TMRP0
0x17
0x18
0x19
0x1A
0x1B
0x1C
0x1D
0x1E
0x1F
0x20
0x21
0x22
0x23
0x24
0x25
0x26
0x27
0x28
0x29
0x2A
0x2B
R/W
R/W
R/W
R
THERM Config2
THERM Config3
THERM Config4
PECI1
P3TH
P2TH
P1TH
PECSTEP PECSTEP PECSTEP PECSTEP SMBSTEP SMBSTEP SMBSTEP SMBSTEP
PSHSTEP PSHSTEP PSHSTEP PSHSTEP SNRSTEP SNRSTEP SNRSTEP SNRSTEP
7
7
7
7
9
6
6
6
6
8
5
5
4
4
3
3
3
3
5
2
2
2
2
4
1
1
1
1
3
0
0
0
0
2
R
PECI2
R
PECI3
5
4
R
Device ID
5
4
R
Vtt measurement
Extended resolution 3
2.5 V Measurement
7
6
R
Vtt
7
Vtt
6
R
9
9
8
8
5
5
4
4
3
3
3
3
3
3
3
3
1
9
1
9
2
2
2
2
2
2
2
2
0
8
0
8
R
V
Measurement
Measurement
7
6
CCP
R
V
CC
9
8
7
6
5
4
R
5 V Measurement
12 V Measurement
Remote 1 Temperature
Local Temperature
Remote 2 Temperature
TACH 1 Low Byte
9
8
7
6
5
4
R
9
8
7
6
5
4
R
9
8
7
6
5
4
R
9
8
7
6
5
4
R
9
8
7
6
5
4
R
7
6
5
4
3
2
R
TACH 1 High Byte
TACH 2 Low Byte
15
7
14
6
13
5
12
4
11
3
10
2
R
R
TACH 2 High Byte
15
14
13
12
11
10
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38
NCT7491
Table 31. REGISTER TABLES
Address R/W
Description
TACH 3 Low Byte
Bit 7
Bit 6
Bit 5
Bit 4
Bit 3
Bit 2
Bit 1
Bit 0
0x2C
0x2D
0x2E
0x2F
0x30
0x31
0x32
0x33
0x34
0x35
0x36
0x37
0x38
0x39
0x3A
0x3B
0x3C
0x3D
0x3E
0x3F
0x40
R
7
15
7
6
14
6
5
13
5
4
12
4
3
2
1
0
R
TACH 3 High Byte
11
10
9
8
R
TACH 4 Low Byte
3
2
1
0
R
TACH 4 High Byte
15
7
14
6
13
5
12
4
11
10
9
8
R/W
R/W
R/W
R
PWM1 Current Duty Cycle
PWM2 Current Duty Cycle
PWM3 Current Duty Cycle
PECI0
3
2
1
0
7
6
5
4
3
2
1
0
7
6
5
4
3
2
1
0
7
6
5
4
3
2
2
1
0
R/W
R/W
R/W
R/W
R/W
R/W
R/W
R/W
R/W
R/W
R
PECI Low Limit
7
6
5
4
3
3
1
0
PECI High Limit
7
6
5
4
2
1
0
PECI configuration Register 1
PECI Config 3
DOM0
AVG2
AVG1
AVG0
PWEN
Rate1
Rate0
RTYDIS
PDET
Max PWM 1 Duty Cycle
Max PWM 2 Duty Cycle
Max PWM 3 Duty Cycle
7
6
5
4
3
3
3
3
2
2
2
2
1
1
1
1
0
0
0
0
7
6
5
4
7
6
5
4
PECI T
7
RANGE
7
6
RANGE
6
5
RANGE
5
4
RANGE
4
MIN
PECI T
RANGE
CONTROL
PECI0 T
3
3
2
1
0
Company ID Number
Version/Revision
Configuration 1
7
6
5
4
2
1
0
R
Ver3
AVELN1
Ver2
AVELN0
Ver1
Ver0
4−wire
PECI
RDY
REV1
LOCK
REV0
STRT
R/W
THERM
Override
PECI
Monitor
Fan
Boost
0x41
0x42
R
R
Interrupt Status 1
Interrupt Status 2
OOL
R2T
LT
R1T
5 V
V
V
2.5 V
12 V
CC
CCP
D2
FAULT
D1
FAULT
FAN4
FAN3
FAN2
FAN1
OOL
0x43
R
Interrupt Status 3
OOL3
DAT2
DAT1
DAT0
OVT
(THERM
Temp
COMM
DATA
PECI0
Limit)
0x44
0x45
0x46
0x47
0x48
0x49
0x4A
0x4B
0x4C
0x4D
0x4E
0x4F
0x50
0x51
0x52
0x53
0x54
0x55
R/W
R/W
R/W
R/W
R/W
R/W
R/W
R/W
R/W
R/W
R/W
R/W
R/W
R/W
R/W
R/W
R/W
R/W
2.5 V Low Limit
2.5 V High Limit
7
7
7
7
7
7
7
7
7
7
7
7
7
7
7
7
7
15
6
6
6
6
6
6
6
6
6
6
6
6
6
6
6
6
6
14
5
5
5
5
5
5
5
5
5
5
5
5
5
5
5
5
5
13
4
4
4
4
4
4
4
4
4
4
4
4
4
4
4
4
4
12
3
3
3
3
3
3
3
3
3
3
3
3
3
3
3
3
3
11
2
2
2
2
2
2
2
2
2
2
2
2
2
2
2
2
2
10
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
9
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
8
V
Low Limit
High Limit
Low Limit
High Limit
CCP
V
CCP
V
CC
V
CC
5 V Low Limit
5 V High Limit
12 V Low Limit
12 V High Limit
Remote 1 Temp Low Limit
Remote 1 Temp High Limit
Local Temp Low Limit
Local Temp High Limit
Remote 2 Temp Low Limit
Remote 2 Temp High Limit
TACH1 Minimum Low Byte
TACH1 Minimum High Byte
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39
NCT7491
Table 31. REGISTER TABLES
Address R/W
Description
Bit 7
7
Bit 6
Bit 5
5
Bit 4
4
Bit 3
3
Bit 2
2
Bit 1
Bit 0
0x56
0x57
0x58
0x59
0x5A
0x5B
0x5C
R/W
R/W
R/W
R/W
R/W
R/W
R/W
TACH2 Minimum Low Byte
TACH2 Minimum High Byte
TACH3 Minimum Low Byte
TACH3 Minimum High Byte
TACH4 Minimum Low Byte
TACH4 Minimum High Byte
6
14
6
1
0
15
7
13
5
12
4
11
3
10
9
8
2
1
0
15
7
14
6
13
5
12
4
11
3
10
9
1
8
0
2
15
14
13
12
INV
11
10
9
8
PWM1 Configuration
Register
SPIN
SPIN
SPIN
0x5D
0x5E
0x5F
0x60
0x61
R/W
R/W
R/W
R/W
R/W
PWM2 Configuration
Register
INV
SPIN
SPIN
SPIN
SPIN
SPIN
SPIN
PWM3 Configuration
Register
INV
Remote 1 T /PWM
RANGE
RANGE
RANGE
RANGE
RANGE
RANGE
RANGE
RANGE
RANGE
RANGE
RANGE
RANGE
RANGE
HF/LF
HF/LF
HF/LF
FREQ
FREQ
FREQ
FREQ
FREQ
FREQ
FREQ
FREQ
FREQ
1 Frequency
Local T /PWM 2
RANGE
Frequency
Remote 2 T /PWM3
RANGE
Frequency
0x62
0x63
0x64
0x65
0x66
0x67
0x68
0x69
0x6A
R/W
R/W
R/W
R/W
R/W
R/W
R/W
R/W
R/W
Enhance Acoustics Reg. 1
Enhance Acoustics Reg. 2
PWM1 Min Duty Cycle
PWM2 Min Duty Cycle
PWM3 Min Duty Cycle
MIN3
MIN2
MIN1
SYNC
EN1
ACOU1
ACOU1
ACOU1
EN2
7
ACOU2
ACOU2
ACOU2
EN3
3
ACOU3
ACOU3
ACOU3
6
6
6
6
6
6
6
5
5
5
5
5
5
5
4
4
4
4
4
4
4
2
2
2
2
2
2
2
1
1
1
1
1
1
1
0
0
0
0
0
0
0
7
3
7
3
Remote 1 Temp T
7
3
MIN
Local Temp T
7
3
MIN
Remote 2 Temp T
7
3
MIN
Remote 1 THERM Temp
Limit
7
3
0x6B
0x6C
R/W
R/W
Local THERM Temp Limit
7
7
6
6
5
5
4
4
3
3
2
2
1
1
0
0
Remote 2 THERM Temp
Limit
0x6D
0x6E
R/W
R/W
Remote 1 and Local
HYSR1
HYSR2
HYSR1
HYSR2
HYSR1
HYSR2
HYSR1
HYRS
HYSL
HYSP
HYSL
HYSP
HYSL
HYSP
HYSL
HYSP
Temp/T
Hysteresis
MIN
Remote 2 and PECI
Temp/T Hysteresis
MIN
0x6F
0x70
R/W
R/W
XNOR Tree Test Enable
XEN
0
Remote 1 Temperature
Offset
7
6
5
4
3
2
1
0x71
0x72
R/W
R/W
Local Temperature Offset
7
7
6
6
5
5
4
4
3
3
2
2
1
1
0
0
Remote 2 Temperature
Offset
0x73
0x74
0x75
0x76
0x77
0x78
R/W
R/W
R/W
R
Configuration Register 2
Interrupt Mask 1 Register
Interrupt Mask 2 Register
Extended Resolution 1
Extended Resolution 2
Config. 3
Shutdown
FQ1
R2T
D1
FQ0
LT
TAVG
RIT
VAVG
5 V
ABS/REL
V
CC
V
2.5 V
12 V
2.5 V
12 V
CCP
D2
5 V
FAN4
FAN3
FAN2
FAN1
5 V
V
CC
V
CC
V
CCP
V
CCP
2.5 V
12 V
R
TDM2
DC4
TDM2
DC3
LTMP
DC2
LTMP
DC1
TDM1
FAST
TDM1
R/W
THERM/2.
5V
ALERT
Enable
0x79
0x7A
R
THERM Timer Value
THERM Timer Limit
TMR
LIMT
TMR
LIMT
TMR
LIMT
TMR
LIMT
TMR
LIMT
TMR
LIMT
TMR
ASRT/
TMRO
R/W
LIMT
LIMT
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40
NCT7491
Table 31. REGISTER TABLES
Address R/W
Description
Bit 7
Bit 6
Bit 5
Bit 4
Bit 3
Bit 2
Bit 1
Bit 0
0x7B
R/W
TACH Pulses per
Revolution
FAN4
FAN4
FAN3
FAN3
FAN2
FAN2
FAN1
FAN1
0x7C
R/W
Configuration Register 5
R2
THERM
O/P
Local
THERM
O/P
R1
THERM
O/P
PECI
THERM
O/P
PIN19
Func
PIN19
Func
Temp
Offset
TWOS
COMPL
0x7D
R/W
Configuration Register 4
BpAtt 12 V
BpAtt
5 V
BpAtt
BpAtt
2.5 V
BpAtt Vtt
THERM
Disable
Pin 14
Func
Pin 14
Func
V
CCP
0x7E
0x7F
0x80
R
Interrupt Status 5
Interrupt Mask 5
OVT_P3
OVT_P2
OVT_P1
OVT_P0
PUSH3
PUSH3
GPIO1
PUSH2
PUSH2
GPIO2
PUSH1
PUSH1
GPEN
PUSH0
PUSH0
R/W
R/W
GPIO Configuration
register
GPIO1
DIR
GPIO2
DIR
GPIO1
POL
GPIO2
POL
0x81
0x82
R
Interrupt Status 4
Interrupt Mask 3
V
TT
SMBCNT
PECI3
PECI2
PECI1
GCOMM
COMM
TTS
PCC
R/W
OVT
THERM
Temp
DATA
PECI0
Limit
0x83
0x84
0x85
0x86
0x87
0x88
0x89
0x8A
0x8B
0x8C
0x8D
0x8E
0x8F
0x90
0x91
0x92
0x93
0x94
0x95
0x96
0x97
0x98
0x99
R/W
R/W
R/W
R/W
R/W
R/W
R
Interrupt Mask 4
V
SMBCNT
6
PECI3
5
PECI2
4
PECI1
3
GCOMM
2
TTS
1
PCC
0
TT
V
TT
Low Limit
7
GPIO Config 2
High Limit
GPIO3 DIR GPIO3 POL
GPIO3
5
V
TT
7
6
4
3
2
1
0
Configuration 9
PECI Config 2
D4V
D3V
D2V
D1V
PWM3OFF PWM2OFF PWM1OFF
#CPU
OOL11
#CPU
OVT_R2
PEC3
SMB6
DOM1
OVT_LOC
PEC2
SMB5
DOM2
OVT_R1
PEC1
SMB4
DOM3
OVT3
PEC0
SMB3
PUSH3
PEC0
SMB3
PUSH3
PEC0
SMB3
PUSH3
3
Interrupt Status 7
OVT2
REM2
SMB2
PUSH2
REM2
SMB2
PUSH2
REM2
SMB2
PUSH2
2
OVT1
REM1
SMB1
PUSH1
REM1
SMB1
PUSH1
REM1
SMB1
PUSH1
1
OVT0
LOC
SMB0
PUSH0
LOC
SMB0
PUSH0
LOC
SMB0
PUSH0
0
R/W
R/W
R/W
R/W
R/W
R/W
R/W
R/W
R/W
PWM1 Source Control 1
PWM1 Source Control 2
PWM1 Source Control 3
PWM2 Source Control 1
PWM2 Source Control 2
PWM2 Source Control 3
PWM3 Source Control 1
PWM3 Source Control 2
PWM3 Source Control 3
Revision
SMB7
SMB7
SMB7
PEC3
SMB6
PEC2
SMB5
PEC1
SMB4
PEC3
SMB6
PEC2
SMB5
PEC1
SMB4
7
7
7
7
7
6
6
6
6
6
6
6
5
5
5
5
5
5
5
4
4
4
4
4
4
4
R/W
R/W
R/W
R/W
R/W
R/W
PECI0 Offset
3
2
1
0
PECI1 Offset
3
2
1
0
PECI2 Offset
3
2
1
0
PECI3 Offset
3
2
1
0
SMB Device0 Address
3
2
1
0
SMB Device 0 Command
Code
7
3
2
1
0
0x9A
0x9B
0x9C
0x9D
0x9E
0x9F
0xA0
0xA1
0xA2
R/W
R/W
R/W
R/W
R/W
R/W
R/W
R/W
R/W
SMB Device1 Address
SMB Device1 Pointer
SMB Device2 Address
SMB Device2 Pointer
SMB Device3 Address
SMB Device3 Pointer
SMB Device4 Address
SMB Device4 Pointer
SMB Device5 Address
6
6
6
6
6
6
6
6
6
5
5
5
5
5
5
5
5
5
4
4
4
4
4
4
4
4
4
3
3
3
3
3
3
3
3
3
2
2
2
2
2
2
2
2
2
1
1
1
1
1
1
1
1
1
0
0
0
0
0
0
0
0
0
7
7
7
7
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41
NCT7491
Table 31. REGISTER TABLES
Address R/W
Description
SMB Device5 Pointer
SMB Device6 Address
SMB Device6 Pointer
SMB Device7 Address
SMB Device7 Pointer
SMB Device0 Value (PCH)
SMB Device1 Value (DIMM0)
SMB Device2 Value (DIMM1)
SMB Device3 Value (DIMM2)
SMB Device4 Value (DIMM3)
SMB Device5 Value
SMB Device6 Value
SMB Device7 Value
SMB Config1
Bit 7
Bit 6
Bit 5
Bit 4
Bit 3
Bit 2
Bit 1
Bit 0
0xA3
0xA4
0xA5
0xA6
0xA7
0xA8
0xA9
0xAA
0xAB
0xAC
0xAD
0xAE
0xAF
0xB0
0xB1
0xB2
0xB3
0xB4
0xB5
0xB6
0xB7
0xB8
0xB9
0xBA
0xBB
0xBC
0xBD
0xBE
0xBF
0xC0
0xC1
0xC2
0xC3
0xC4
0xC5
0xC6
0xC7
0xC8
0xC9
0xCA
0xCB
0xCC
0xCD
0xCE
0xCF
R/W
R/W
R/W
R/W
R/W
R
7
6
5
4
3
2
1
0
6
5
4
3
2
1
0
7
6
5
4
3
2
1
0
6
5
4
3
2
1
0
7
6
5
4
3
2
1
0
7
6
5
4
3
2
1
0
R
7
6
5
4
3
2
1
0
R
7
6
5
4
3
2
1
0
R
7
6
5
4
3
2
1
0
R
7
7
6
6
5
5
4
4
3
3
2
2
1
1
0
0
R
R
7
6
5
4
3
2
1
0
R
7
6
5
4
3
2
1
0
R/W
R/W
R/W
R/W
R
RS7
PEC7
TFMT3
TFMT7
RS6
PEC6
TFMT3
TFMT7
RS5
PEC5
TFMT2
TFMT6
RS4
PEC4
TFMT2
TFMT6
RS3
PEC3
TFMT1
TFMT5
RS2
PEC2
TFMT1
TFMT5
RS1
PEC1
TFMT0
TFMT4
RS0
PEC0
TFMT0
TFMT4
SMB Config2
SMB Config3
SMB Config4
Reserved
R/W
R
SMB Config5
PCHDIMM
R2DIMM
R1DIMM
NACK5
PEC5
TO5
HILO5
TIV5
TH5
NACK5
PC5
TO5
HILO5
TIV5
5
SHYS3
NACK4
PEC4
TO4
HILO4
TIV4
TH4
NACK4
PC4
TO4
HILO4
TIV4
4
SHYS2
SHYS1
SHYS0
SMBMEN
SMB Status 1
NACK7
NACK6
NACK3
NACK2
NACK1
NACK0
R
SMB Status 2
PEC7
PEC6
PEC3
PEC2
PEC1
PEC0
R
SMB Status 3
TO7
TO6
TO3
TO2
TO1
TO0
R
SMB Status 4
HILO7
HILO6
HILO3
HILO2
HILO1
HILO0
R
SMB Status 5
TIV7
TIV6
TIV3
TIV2
TIV1
TIV0
R
SMB Status 6
TH7
TH6
TH3
TH2
TH1
TH0
R/W
R/W
R/W
R/W
R/W
R/W
R/W
R/W
R
SMB Mask 1
NACK7
NACK6
NACK3
NACK2
NACK1
NACK0
SMB Mask 2
PC7
PC6
PC3
PC2
PC1
PC0
SMB Mask 3
TO7
TO6
TO3
TO2
TO1
TO0
SMB Mask 4
HILO7
HILO6
HILO3
HILO2
HILO1
HILO0
SMB Mask 5
TIV7
TIV6
TIV3
TIV2
TIV1
TIV0
SMB High Limit
SMB Low Limit
7
6
3
2
1
0
7
6
5
4
3
2
1
0
SMB THERM Limit
Reserved
7
6
5
4
3
2
1
0
7
6
5
4
3
2
1
0
R
Reserved
7
6
5
4
3
2
1
0
R/W
R/W
R/W
R/W
R/W
R/W
R/W
R/W
R/W
R/W
SMB Device Tmin
SMB Device Trange
Push0 Value
7
6
5
4
3
2
1
0
SMBINT1
SMBINT0
RNG
RNG
RNG
RNG
7
7
7
7
7
6
6
6
6
6
5
5
5
5
5
4
4
4
4
4
3
2
1
0
Push1 Value
3
2
1
0
Push2 Value
3
2
1
0
Push3 Value
3
3
2
2
1
1
0
0
Push Tmin
Push Trange
RNG
3
RNG
2
RNG
1
RNG
0
Push High Limit
Push Low Limit
7
7
6
6
5
5
4
4
3
2
1
0
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42
NCT7491
Table 31. REGISTER TABLES
Address R/W
Description
Push THERM Limit
Generic PECI Address
Write Length
Read Length
WRDAT0
Bit 7
7
Bit 6
Bit 5
5
Bit 4
4
Bit 3
3
Bit 2
2
Bit 1
1
Bit 0
0
0xD0
0xD1
0xD2
0xD3
0xD4
0xD5
0xD6
0xD7
0xD8
0xD9
0xDA
0xDB
0xDC
0xDD
0xDE
0xDF
0xE0
0xE1
0xE2
0xE3
0xE4
0xE5
0xE6
0xE7
0xE8
0xE9
0xEA
0xEB
R/W
R/W
R/W
R/W
R/W
R/W
R/W
R/W
R/W
R/W
R/W
R/W
R/W
R/W
R/W
R/W
R/W
R/W
R/W
R/W
R/W
R/W
R/W
R/W
R/W
R/W
R/W
R/W
R
6
6
6
6
6
6
6
6
6
6
6
6
6
6
6
6
6
6
6
6
6
6
6
6
6
6
7
5
4
3
2
1
0
7
5
4
3
2
1
0
7
5
4
3
2
1
0
7
5
4
3
2
1
0
WRDAT1
7
5
4
3
2
1
0
WRDAT2
7
5
4
3
2
1
0
WRDAT3
7
5
4
3
2
1
0
WRDAT4
7
5
4
3
2
1
0
WRDAT5
7
5
4
3
2
1
0
WRDAT6
7
5
4
3
2
1
0
WRDAT7
7
5
4
3
2
1
0
WRDAT8
7
5
4
3
2
1
0
WRDAT9
7
5
4
3
2
1
0
WRDAT10
WRDAT11
WRDAT12
RDDAT0
7
5
4
3
2
1
0
7
5
4
3
2
1
0
7
5
4
3
2
1
0
7
5
4
3
2
1
0
RDDAT1
7
5
4
3
2
1
0
RDDAT2
7
5
4
3
2
1
0
RDDAT3
7
5
4
3
2
1
0
RDDAT4
7
5
4
3
2
1
0
RDDAT5
7
5
4
3
2
1
0
RDDAT6
7
5
4
3
2
1
0
RDDAT7
7
5
4
3
2
1
0
RDDAT8
7
5
4
3
2
1
0
PECI Config 5
Push Hyst
Reserved
PEX
AW
PushHys3 PushHys2 PushHys1 PushHys0
0xEC
to 0xFE
0xFF
0x100
0x101
0x102
0x103
0x104
0x105
0x106
0x107
0x108
0x109
0x10A
0x10B
0x10C
0x10D
R/W
R/W
R/W
R/W
R/W
R/W
R/W
R/W
R/W
R/W
R/W
R/W
R/W
R/W
R/W
Page Select
RGMP
Fan1 LUT Temp1
Fan1 LUT PWM1
Fan1 LUT Temp2
Fan1 LUT PWM2
Fan1 LUT Temp3
Fan1 LUT PWM3
Fan1 LUT Temp4
Fan1 LUT PWM4
Fan1 LUT Temp5
Fan1 LUT PWM5
Fan1 LUT Temp6
Fan1 LUT PWM6
Fan1 LUT Temp7
Fan1 LUT PWM7
7
7
7
7
7
7
7
7
7
7
7
7
7
7
6
6
6
6
6
6
6
6
6
6
6
6
6
6
5
5
5
5
5
5
5
5
5
5
5
5
5
5
4
4
4
4
4
4
4
4
4
4
4
4
4
4
3
3
3
3
3
3
3
3
3
3
3
3
3
3
2
2
2
2
2
2
2
2
2
2
2
2
2
2
1
1
1
1
1
1
1
1
1
1
1
1
1
1
0
0
0
0
0
0
0
0
0
0
0
0
0
0
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43
NCT7491
Table 31. REGISTER TABLES
Address R/W
Description
Fan1 LUT Temp8
Fan1 LUT PWM8
Fan2 LUT Temp1
Fan2 LUT PWM1
Fan2 LUT Temp2
Fan2 LUT PWM2
Fan2 LUT Temp3
Fan2 LUT PWM3
Fan2 LUT Temp4
Fan2 LUT PWM4
Fan2 LUT Temp5
Fan2 LUT PWM5
Fan2 LUT Temp6
Fan2 LUT PWM6
Fan2 LUT Temp7
Fan2 LUT PWM7
Fan2 LUT Temp8
Fan2 LUT PWM8
Fan3 LUT Temp1
Fan3 LUT PWM1
Fan3 LUT Temp2
Fan3 LUT PWM2
Fan3 LUT Temp3
Fan3 LUT PWM3
Fan3 LUT Temp4
Fan3 LUT PWM4
Fan3 LUT Temp5
Fan3 LUT PWM5
Fan3 LUT Temp6
Fan3 LUT PWM6
Fan3 LUT Temp7
Fan3 LUT PWM7
Fan3 LUT Temp8
Fan3 LUT PWM8
Reserved
Bit 7
7
7
7
7
7
7
7
7
7
7
7
7
7
7
7
7
7
7
7
7
7
7
7
7
7
7
7
7
7
7
7
7
7
7
Bit 6
Bit 5
5
5
5
5
5
5
5
5
5
5
5
5
5
5
5
5
5
5
5
5
5
5
5
5
5
5
5
5
5
5
5
5
5
5
Bit 4
4
4
4
4
4
4
4
4
4
4
4
4
4
4
4
4
4
4
4
4
4
4
4
4
4
4
4
4
4
4
4
4
4
4
Bit 3
3
3
3
3
3
3
3
3
3
3
3
3
3
3
3
3
3
3
3
3
3
3
3
3
3
3
3
3
3
3
3
3
3
3
Bit 2
2
2
2
2
2
2
2
2
2
2
2
2
2
2
2
2
2
2
2
2
2
2
2
2
2
2
2
2
2
2
2
2
2
2
Bit 1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
Bit 0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0x10E
0x10F
0x110
0x111
0x112
0x113
0x114
0x115
0x116
0x117
0x118
0x119
0x11A
0x11B
0x11C
0x11D
0x11E
0x11F
0x120
0x121
0x122
0x123
0x124
0x125
0x126
0x127
0x128
0x129
0x12A
0x12B
0x12C
0x12D
0x12E
0x12F
R/W
R/W
R/W
R/W
R/W
R/W
R/W
R/W
R/W
R/W
R/W
R/W
R/W
R/W
R/W
R/W
R/W
R/W
R/W
R/W
R/W
R/W
R/W
R/W
R/W
R/W
R/W
R/W
R/W
R/W
R/W
R/W
R/W
R/W
6
6
6
6
6
6
6
6
6
6
6
6
6
6
6
6
6
6
6
6
6
6
6
6
6
6
6
6
6
6
6
6
6
6
0x130−
0x1CF
0x1D0
0x1D1
0x1D2
0x1D3
0x1D4
0x1D5
0x1D6
0x1D7
0x1D8
R/W
R/W
R/W
R/W
R/W
R/W
R/W
R/W
R/W
Test Reg 1
Test Reg 2
Test Reg 3
Test Reg 4
Test Reg 5
Test Reg 6
Test Reg 7
Test Reg 8
Test Reg 9
7
7
7
7
7
7
7
7
7
6
6
6
6
6
6
6
6
6
5
5
5
5
5
5
5
5
5
4
4
4
4
4
4
4
4
4
3
3
3
3
3
3
3
3
3
2
2
2
2
2
2
2
2
2
1
1
1
1
1
1
1
1
1
0
0
0
0
0
0
0
0
0
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NCT7491
Table 31. REGISTER TABLES
Address R/W
Description
Bit 7
Bit 6
Bit 5
Bit 4
Bit 3
Bit 2
Bit 1
Bit 0
0x1D9 –
0x1DF
Reserved
0x1E0
0x1E1
0x1E2
0x1E3
0x1e4
0x1E5
0x1E6
0x1E7
0x1E8
0x1E9
0x1EA
0x1EB
0x1FF
R/W
R/W
R/W
R/W
R/W
R/W
R/W
R/W
R/W
R/W
R/W
R/W
R/W
Fuse Reg 1
Fuse Reg 2
Fuse Reg 3
Fuse Reg 4
Fuse Reg 5
Fuse Reg 6
Fuse Reg 7
Fuse Reg 8
Fuse Reg 9
Fuse Reg 10
Fuse Reg 11
Fuse Reg 12
Page Select Clear
7
7
7
7
7
7
7
7
7
7
7
7
6
6
6
6
6
6
6
6
6
6
6
6
5
5
5
5
5
5
5
5
5
5
5
5
4
4
4
4
4
4
4
4
4
4
4
4
3
3
3
3
3
3
3
3
3
3
3
3
2
2
2
2
2
2
2
2
2
2
2
2
1
1
1
1
1
1
1
1
1
1
1
1
0
0
0
0
0
0
0
0
0
0
0
0
RGMPCL
Table 32. PECI ADDRESS REGISTERS (Note 1) (Power−On Default = 0x00)
Register Address
R/W
R/W
R/W
R/W
R/W
Description
0x00
0x01
0x02
0x03
PECI0 CPU Address
PECI1 CPU Address
PECI2 CPU Address
PECI3 CPU Address
1. These registers are automatically populated when the PECI interface is enabled. They can be over−written if necessary.
Table 33. PECI_Abs REGISTERS (Note 2) (Power−On Default = 0x00)
Register Address
R/W
R/W
R/W
R/W
R/W
Description
0x04
0x05
0x06
0x07
PECI0 absolute value. 8 bit unsigned.
PECI1 absolute value. 8 bit unsigned.
PECI2 absolute value. 8 bit unsigned.
PECI3 absolute value. 8 bit unsigned.
2. These registers return the absolute CPU temperature calculated using the Tjmax value for each PECI channel.
Table 34. PECI Tcontrol LIMIT REGISTERS (Note 3) (Power−On Default = 0x00)
Register Address
R/W
R/W
R/W
R/W
R/W
Description
PECI0 Tcontrol
PECI1 Tcontrol
PECI2 Tcontrol
PECI3 Tcontrol
0x3D
0x08
0x09
0x0A
3. If any PECI reading exceeds its T
limit, all PWM outputs drive their fans at 100% duty cycle. This is a fail−safe mechanism
CONTROL
incorporated to cool the system in the event of a critical over−temperature. It also ensures some level of cooling in the event that software
or hardware locks up. If set to 0x80, this feature is disabled. The PWM output remains at 100% until the temperature drops below T
limit − hysteresis.
CONTRO
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NCT7491
Table 35. PECI TJMAX REGISTERS (Note 4) (Power−On Default = 0x00)
Register Address
R/W
R
Description
PECI0 Tjmax
PECI1 Tjmax
PECI2 Tjmax
PECI3 Tjmaxl
0x0B
0x0C
0x0D
0x0E
R
R
R
4. The maximum junction temperature for each CPU is returned in these registers. These are automatically read from the PECI interface on
power−up
Table 36. REGISTER 0x0F − PECI Configuration Register 4 (Power−On Default = 0x00)
Bit
Mnemonic
R/W
Description
<1:0>
DM0CPU
R/W
Sets the DIMM0 CPU assignment:
00 = CPU0
01 = CPU1
10 = CPU2
11 = CPU3
<3:2>
<5:4>
<7:6>
DM1CPU
DM2CPU
DM3CPU
R/W
R/W
R/W
Sets the DIMM1 CPU assignment:
00 = CPU0
01 = CPU1
10 = CPU2
11 = CPU3
Sets the DIMM2 CPU assignment:
00 = CPU0
01 = CPU1
10 = CPU2
11 = CPU3
Sets the DIMM3 CPU assignment:
00 = CPU0
01 = CPU1
10 = CPU2
11 = CPU3
Table 37. REGISTER 0x10 − Configuration Register 6 (Power−On Default = 0x18)
Bit
Mnemonic
R/W
Description
<0>
PWM1Mode
R/W
0 = PWM1 uses Tmin/Trange control
1 = PWM1 uses LUT control
<1>
<2>
PWM2Mode
PWM3Mode
R/W
R/W
R/W
0 = PWM 2 uses Tmin/Trange control
1 = PWM2 uses LUT control
0 = PWM3 uses Tmin/Trange control
1 = PWM3 uses LUT control
<4:3>
SMBRT
(Note 5)
Sets the SMBus Master Retry delay time:
00 = 1 ms
01 = 2 ms
10 = 4 ms
11 = 8 ms
<5>
IFT
R/W
1 = Ignore first tach pulse during tach measurement. This can be used to stabilize readings from
fans that produce erroneous glitches in 3−wire mode.
5. If an error occurs in the SMBus Master sequence then the interface will attempt to read from the slave device again. The interval between
read attempts is set by SMBRT
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NCT7491
Table 37. REGISTER 0x10 − Configuration Register 6 (Power−On Default = 0x18)
Bit
Mnemonic
Low
R/W
Description
<6>
V
R/W
VCCPLow = 1. When the power is supplied from 3.3 V STANDBY and the core voltage (VCCP)
drops below its VCCP low limit value (Reg. 0x46), the following occurs:
CCP
Status Bit 1 in Status Register 1 is set.
SMBALERT is generated, if enabled.
PROCHOT monitoring is disabled.
Everything is re−enabled once VCCP increases above the VCCP low limit.
When VCCP increases above the low limit:
PROCHOT monitoring is enabled.
Fans return to their programmed state after a spin−up cycle.
<7>
Reserved
R
5. If an error occurs in the SMBus Master sequence then the interface will attempt to read from the slave device again. The interval between
read attempts is set by SMBRT
Table 38. REGISTER 0x11 − Configuration Register 7 (Power−On Default = 0x04)
Bit
Mnemonic
R/W
Description
<0>
THERMHys
R/W
Setting this bit to 1 enables THERM hysteresis. Note that hysteresis on THERM is disabled
by default. To enable hysteresis this bit must be set to logic 1 and also bit <2> of register
0x7D must be cleared to 0.
<1>
FSPD
R/W
When set to 1, this bit runs all fans at max speed as programmed in the max PWM duty
cycle registers (0x38 to 0x3A). Power−on default = 0. This bit is not locked at any time.
<2>
<3>
Vtt
R/W
R/W
Setting this bit to 1 includes Vtt in the analog monitoring cycle
FSPDIS
Logic 1 disables fan spin−up for two TACH pulses. Instead, the PWM outputs go high for the
entire fan spin−up timeout selected.
<4>
TODIS
R/W
When this bit is set to 1, the SMBus timeout feature is disabled.
In this state, if at any point during an SMBus transaction involving the NCT7491 activity
ceases for more than 35 ms, the NCT7491 assumes the bus is locked and releases the bus.
This allows the NCT7491 to be used with SMBus controllers that cannot handle SMBus
timeouts. (Lockable.)
<5>
<6>
<7>
SMBFS1
SMBFS2
SMBFS3
R/W
R/W
R/W
PWM1 response to 3 consecutive SMBus Slave device errors; 0=no response; 1=PWM1 go
to max speed or 100%
PWM2 response to 3 consecutive SMBus Slave device errors; 0=no response; 1=PWM2 go
to max speed or 100%
PWM3 response to 3 consecutive SMBus Slave device errors; 0=no response; 1=PWM3 go
to max speed or 100%
Table 39. REGISTER 0x12 − Interrupt Status 6 (Power−On Default = 0x00)
Bit
Mnemonic
OOL0
R/W
R
Description
<0>
<1>
<2>
<3>
<4>
<5>
<6>
<7>
1 = ALERT assertion in register 0x41
1 = ALERT assertion in register 0x7E
1 = ALERT assertion in register 0xB6
1 = ALERT assertion in register 0xB7
1 = ALERT assertion in register 0xB8
1 = ALERT assertion in register 0xB9
1 = ALERT assertion in register 0xBA
1 = ALERT assertion in register 0x89
OOL4
R
OOL5
R
OOL6
R
OOL7
R
OOL8
R
OOL9
R
OOL10
R
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NCT7491
Table 40. REGISTER 0x13 − Configuration Register 8 (Power−On Default = 0xFF)
Bit
Mnemonic
Local
Rem1
Rem2
12V
R/W
R/W
R/W
R/W
R/W
R/W
R/W
R/W
R/W
Description
<0>
<1>
<2>
<3>
<4>
<5>
<6>
<7>
Setting this bit to 1 includes Local temperature in the analog monitoring cycle
Setting this bit to 1 includes Rem1 temperature in the analog monitoring cycle
Setting this bit to 1 includes Rem2 temperature in the analog monitoring cycle
Setting this bit to 1 includes 12V in the analog monitoring cycle
Setting this bit to 1 includes 5V in the analog monitoring cycle
Setting this bit to 1 includes Vccp in the analog monitoring cycle
Setting this bit to 1 includes 2.5V in the analog monitoring cycle
Setting this bit to 1 includes Vcc in the analog monitoring cycle errors.
5V
Vccp
2.5V
Vcc
Table 41. PWM STEPPING LEVEL REGISTERS (Power−On Default = 0x00)
Register Address
Register
PWMStep1
PWMStep2
R/W
R/W
R/W
Description
0x14
0x15
Sets the PWM level on a THERM assertion if THERM stepping is enabled
Sets the PWM level if THERM stepping is enabled and the temperature is greater
than THERM + Step (Note 6)
6. The temperature interval for each step is programmed in registers 0x18 and 0x19
Table 42. REGISTER 0x16 − THERM Configuration Register 1 (Power−On Default = 0x1C)
Bit
Mnemonic
R/W
Description
<1:0>
TMRP
R/W
00 = Disabled
01 = Pin 14 (QSOP), Pin 11 (QFN) is THERM timer input
10 = Pin 19 (QSOP), Pin 16 (QFN) is THERM timer input
11 = Pin 22 (QSOP), Pin 19 (QFN) is THERM timer input
<2>
<3>
<4>
<5>
<6>
<7>
Max/Full 1
Max/Full 2
Max/Full 3
R/W
R/W
R/W
R/W
R/W
R
1= PWM1 goes to 100% on THERM
0= PWM1 goes to Max programmed PWM on THERM
1= PWM2 goes to 100% on THERM
0= PWM2 goes to Max programmed PWM on THERM
1= PWM3 goes to 100% on THERM
0= PWM3 goes to Max programmed PWM on THERM
Push
THERM
1 = THERM assertions enabled for Push temperatures
0 = THERM assertions disabled for Push temperatures
SMBus
THERM
1 = THERM assertions enabled for SMBus slave temperatures
0 = THERM assertions disabled for SMBus slave temperatures
Reserved
Table 43. REGISTER 0x17 − THERM Configuration Register 2 (Power−On Default = 0x07)
Bit
Mnemonic
P1TH
R/W
R/W
R/W
R/W
R
Description
If set to 1 then PWM1 will respond to THERM events
If set to 1 then PWM2 will respond to THERM events
If set to 1 then PWM3 will respond to THERM events
<0>
<1>
<2>
<3>
<4>
<5>
<6>
<7>
P2TH
P3TH
Reserved
Reserved
Reserved
Reserved
Reserved
R
R
R
R
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NCT7491
Table 44. REGISTER 0x18 − THERM Configuration Register 3 (Power−On Default = 0x00)
Bit
Mnemonic
R/W
Description
<3:0>
SMBSTEP
R/W
Sets the Step size used by the THERM stepping function when applied to SMBus Master
device THERM assertions
<7:4>
PECSTEP
R/W
Sets the Step size used by the THERM stepping function when applied to PECI Tcontrol
assertions
Table 45. REGISTER 0x19 − THERM Configuration Register 4 (Power−On Default = 0x00)
Bit
Mnemonic
R/W
Description
<3:0>
SNRSTEP
R/W
Sets the Step size used by the THERM stepping function when applied to Remote1/Local/
Remote2 sensor THERM assertions
<7:4>
PSHSTEP
R/W
Sets the Step size used by the THERM stepping function when applied to Push temperature
THERM assertions
Table 46. PECI READING REGISTERS (Power−On Default = 0x80)
Register Address
R/W
R
Description
PECI0: This register reads the 8 bits representative of PECI0
PECI1: This register reads the 8 bits representative of PECI1
PECI2: This register reads the 8 bits representative of PECI2
PECI3: This register reads the 8 bits representative of PECI 3
0x33
0x1A
0x1B
0x1C
R
R
R
Table 47. DEVICE ID REGISTER (Power−On Default = 0x91)
Register Address
R/W
Description
Power−On Default
0x1D
R
Device ID
0x91
Table 48. VTT READING REGISTER (Power−On Default = 0x00)
Register Address
R/W
Description
0x1E
R
Reflects the voltage measurement at the V input on Pin 8 of the QSOP package, Pin 5 of the
QFN package (8 MSBs of reading). Input range of 0 to 2v
TT
Table 49. REGISTER 0x1F EXTENDED RESOLUTION 3 (Power−On Default = 0x00)
Bits
R/W
R
Description
<3:0>
<5:4>
<7:6>
RESERVED
R
Bits <5:4> hold the two LSB’s of the 10−bit V measurement
TT
R
RESERVED
Table 50. VOLTAGE READING REGISTERS (Power−On Default = 0x00) (Note 7)
Register Address
R/W
Description
0x20
R
Reflects the voltage measurement at the 2.5 V input on Pin 22 of the QSOP package, Pin 19 of
the QFN package (8 MSBs of reading).
0x21
0x22
0x23
0x24
R
R
R
R
Reflects the voltage measurement (Note 8) at the V
Pin 20 of the QFN package (8 MSBs of reading).
input on Pin 23 of the QSOP package,
CCP
Reflects the voltage measurement (Note 9) at the V input on Pin 4 of the QSOP package,
CC
Pin 1 of the QFN package (8 MSBs of reading).
Reflects the voltage measurement at the 5 V input on Pin 20 of the QSOP package, Pin 17 of
the QFN package (8 MSBs of reading).
Reflects the voltage measurement at the 12 V input on Pin 21 of the QSOP package, Pin 18 of
the QFN package (8 MSBs of reading).
7. If the extended resolution bits of these readings are also being read, the extended resolution registers (Reg. 0x76, 0x77) must be read first.
Once the extended resolution registers have been read, the associated MSB reading registers are frozen until read. Both the extended
resolution registers and the MSB registers are frozen.
8. If V
Low (Bit 6 of 0x10) is set, V
can control the sleep state of the NCT7491.
CCP
CCP
9. V (Pin 4 on the QSOP package, Pin1 on the QFN package) is the supply voltage for the NCT7491.
CC
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NCT7491
Table 51. TEMPERATURE READING REGISTERS (Power−On Default = 0x80) (Notes 10, 11, 12)
Register Address
R/W
R
Description
0x25
0x26
0x27
Remote 1 temperature reading (Notes 12, 13) (8 MSB of reading).
Local temperature reading (8 MSB of reading).
R
R
Remote 2 temperature reading (Notes 12, 13) (8 MSB of reading).
10.If the extended resolution bits of these readings are also being read, the extended resolution registers (Reg. 0x76, 0x77) must be read first.
Once the extended resolution registers have been read, all associated MSB reading registers are frozen until read. Both the extended
resolution registers and the MSB registers are frozen.
11. These temperature readings can be in twos complement or offset 64 format; this interpretation is determined by Bit 0 of Configuration Register
5 (0x7C).
12.In twos complement mode, a temperature reading of −128°C (0x80) indicates a diode fault (open or short) on that channel.
13.In offset 64 mode, a temperature reading of −64°C (0x00) indicates a diode fault (open or short) on that channel.
Table 52. FAN TACHOMETER READING REGISTERS (Power−On Default = 0x00) (Note 14)
Register Address
0x28
R/W
R
Description
TACH1 low byte.
TACH1 high byte.
TACH2 low byte.
TACH2 high byte.
TACH3 low byte.
TACH3 high byte.
TACH4 low byte.
TACH4 high byte.
0x29
R
0x2A
R
0x2B
R
0x2C
R
0x2D
R
0x2E
R
0x2F
R
14.These registers count the number of 11.11 ms periods (based on an internal 90 kHz clock) that occur between a number of consecutive fan
TACH pulses (default = 2). The number of TACH pulses used to count can be changed using the fan pulses per revolution register (Reg.
0x7B). This allows the fan speed to be accurately measured. Because a valid fan tachometer reading requires that two bytes be read, the
low byte must be read first. Both the low and high bytes are then frozen until read. At power−on, these registers contain 0x0000 until the first
valid fan TACH measurement is read into these registers. This prevents false interrupts from occurring while the fans are spinning up.
A count of 0xFFFF indicates that a fan is one of the following: stalled or blocked (object jamming the fan), failed (internal circuitry destroyed),
or not populated. (The NCT7491 expects to see a fan connected to each TACH. If a fan is not connected to that TACH, its TACH minimum
high and low bytes should be set to 0xFF.)
Table 53. CURRENT PWM DUTY CYCLE REGISTERS (Power−On Default = 0xFF) (Note 15)
Register Address
R/W
R/W
R/W
R/W
Description
0x30
0x31
0x32
PWM1 current duty cycle (0% to 100% duty cycle = 0x00 to 0xFF).
PWM2 current duty cycle (0% to 100% duty cycle = 0x00 to 0xFF).
PWM3 current duty cycle (0% to 100% duty cycle = 0x00 to 0xFF).
15.These registers reflect the PWM duty cycle driving each fan at any given time. When in automatic fan speed control mode, the NCT7491
reports the PWM duty cycles back through these registers. The PWM duty cycle values vary according to temperature in automatic fan speed
control mode. During fan startup, these registers report back 0x00. In manual mode, the PWM duty cycle outputs can be set to any duty cycle
value by writing to these registers.
Table 54. REGISTER 0x33 PECI0 READING REGISTER (Power−On Default = 0x80)
Register Address
R/W
Description
0x33
R
PECI0: This register reads the 8 bits representative of PECI Client Address stored in register 0x00
Table 55. PECI LIMIT REGISTERS REGISTER
Register Address
R/W
R/W
R/W
Description
PECI Low Limit
PECI High Limit
Power−On Default
0x34
0x35
0x81
0x00
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Table 56. REGISTER 0x36 PECI CONFIGURATION REGISTER 1 (Power−On Default = 0x00)
BIT
NAME
R/W
Description
<2:0>
AVG
R/W
PECI Averaging Count
Code
000
001
010
011
100
101
110
111
Averaged Samples
1
2
4
8
Reserved
Reserved
Reserved
Reserved
<3>
DOM0
R/W
CPU Domain Count information. Set to 0 indicates that CPU 1 associated with the PECI0 reading
has a single domain (Default). Set to 1 indicates that the system CPU 1 contains two domains.
<4>
<5>
Reserved
Reserved
Reserved
<7:6>
Table 57. REGISTER 0x37 PECI CONFIGURATION REGISTER 3 (Power−On Default = 0x32)
Bit
Name
R/W
Description
<0>
PDET
R/W
1 = at least one PECI enabled processor detected
0 = no processors detected
<1>
RTYDIS
R/W
1 = PECI retry bit is disabled
0 = PECI retry bit is enabled
This bit allows the user to disable the PECI retry bit for any subsequent commands following a
bad Completion Code from the CPU. It is enabled by default.
<2>
<3>
Reserved
Reserved
Rate
R
R
<5:4>
R/W
PECI update rate
00 = 1/sec
01 = 2/sec
10 = 5/sec
11 = 10/sec
<6>
<7>
Reserved
PWEN
R/W
1=PECI CPU writes are enabled
0=PECI CPU writes are disabled
Table 58. MAXIMUM PWM DUTY CYCLE (Power−On Default = 0xFF) (Note 16)
2
Register Address
R/W
R/W
R/W
R/W
Description
0x38
0x39
0x3A
Maximum duty cycle for PWM1 output, default = 100% (0xFF.)
Maximum duty cycle for PWM2 output, default = 100% (0xFF).
Maximum duty cycle for PWM3 output, default = 100% (0xFF).
16.These registers set the maximum PWM duty cycle of the PWM output.
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Table 59. PECI TMIN REGISTER (Power−On Default = 0x80)
Register Address
R/W
Description
Power−On Default
0x3B
R/W
PECI T
0xD6 (−42°C)
MIN
When the PECI measurement exceeds PECI T
the appropriate fans run at
MIN
PWM
and increase according to the automatic fan speed control slope.
MIN
If Absolute PECI mode is used then the maximum valid Tmin value is 175°C.
Table 60. REGISTER 0x3C − PECI TRANGE (Power−On Default = 0xC0)
1
Bit
Name
R/W
R
Description
<2:0>
< 3 >
<7:4>
Reserved
Reserved
R
T
R/W
These bits determine the PWM duty cycle vs. the PECI temperature range for automatic
RANGE
fan control.
0000 = 2°C
0001 = 2.5°C
0010 = 3.33°C
0011 = 4°C
0100 = 5°C
0101 = 6.67°C
0110 = 8°C
0111 = 10°C
1000 = 13.33°C
1001 = 16°C
1010 = 20°C
1011 = 26.67°C
1100 = 32°C (default)
1101 = 40°C
1110 = 53.33°C
1111 = 80°C
Table 61. PECI0 TCONTROL LIMIT REGISTER (Note 17)
Register Address
0x3D
R/W
R/W
Description
PECI0 T
Power−On Default
limit.
0x00
CONTROL
17.If any PECI reading exceeds the T
limit, all PWM outputs drive their fans at 100% duty cycle. This is a fail−safe mechanism
CONTROL
incorporated to cool the system in the event of a critical overtemperature. It also ensures some level of cooling in the event that software
or hardware locks up. If set to 0x80, this feature is disabled. The PWM output remains at 100% until the temperature drops below T
limit − hysteresis.
CONTRO
Table 62. COMPANY ID REGISTER
Register Address
R/W
Description
Power−On Default
0x1A
0x3E
Read
Company ID
Table 63. REGISTER 0x3F VERSION/REVISION REGISTER (Power−On−Default = 0x6C)
Bit
Name
R/W
Description
<1:0>
REV
Read
These two bits indicate the NCT7491 silicon revision number. 0x00 indicates rev 0, 0x01 indic-
ates Rev 1 etc…
<2>
<3>
PECI
Read
Read
This bit is set to 1 indicating that the NCT7491 supports the PECI interface
4 Wire
This bit is set to 1 indicating that the NCT7491 may be configured to drive 4−wire fans using high
frequency PWM.
<7:4>
VER
Read
These bits indicate the Heceta version number of the device.
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Table 64. REGISTER 0x40 − Configuration Register 1 (Power−On Default = 0x84)
Bit
Name
R/W
Description
<0>
STRT
(Notes 18, 19)
R/W
Logic 1 enables monitoring and PWM control outputs based on the limit settings programmed.
Logic 0 disables monitoring and PWM control is based on the default power−up limit settings.
Note that the limit values programmed are preserved even if a Logic 0 is written to this bit and
the default settings are enabled. This bit does not become locked once Bit 1 (LOCK bit) has
been set.
<1>
LOCK
Write once
Logic 1 locks all limit values to their current settings. Once this bit is set, all lockable registers
become read−only and cannot be modified until the NCT7491 is powered down and powered
up again. This prevents rogue programs such as viruses from modifying critical system limit
settings. (Lockable.)
<2>
<3>
RDY
R
This bit is set to 1 by the NCT7491 to indicate that the device is fully powered−up and ready
to begin system monitoring.
Fan Boost
R/W
When this bit is set to logic 1 all PWM outputs go to 100% regardless of other fan speed
configurations and automatic fan speed control settings. When this bit is set to 0 the fan
speed control returns to the fan speed setting calculated by the pre−programmed fan speed
control settings. This bit remains writable after the lock bit is set.
<4>
<5>
PECI Monitor
R/W
R/W
Set this bit to logic 1 to enable CPU thermal monitoring via PECI interface. This bit becomes
read only when the lock bit is set.
THERM
Override
When this bit is set to logic 1, any THERM pin assertion will cause the fans to go to 100% or
Max PWM, depending on bits <4:2> of register 0x16, overriding any other fan setting, even
when the PWM’s are configured for manual mode, or disabled. This bit becomes read only
when the lock bit is set.
<7:6>
AVELN
R/W
Sets the averaging length for all analog channels
00 = 4 readings per averaged value
01 = 8 readings per averaged value
10 = 16 readings per averaged value
11 = 32 readings per averaged value
18.Bit 0 (STRT) of Configuration Register 1 (0x40) remains writable after lock bit is set.
19.When monitoring (STRT) is disabled, PWM outputs always go to 100% for thermal protection.
Table 65. REGISTER 0x41 − Interrupt Status Register 1 (Power−On Default = 0x00)
Bit
Name
R/W
Description
<0>
2.5 V
R
2.5 V = 1 indicates that the 2.5 V high or low limit has been exceeded. This bit is cleared on a read of
the status register only if the error condition has subsided.
<1>
<2>
<3>
<4>
<5>
<6>
<7>
V
R
R
R
R
R
R
R
V
= 1 indicates that the V
high or low limit has been exceeded. This bit is cleared on a read of
CCP
CCP
CCP
the status register only if the error condition has subsided.
V = 1 indicates that the V high or low limit has been exceeded. This bit is cleared on a read of
CC
V
CC
CC
the status register only if the error condition has subsided.
5 V
RIT
LT
A 1 indicates that the 5 V high or low limit has been exceeded. This bit is cleared on a read of the
status register only if the error condition has subsided.
RIT = 1 indicates that the Remote 1 low or high temperature has been exceeded. This bit is cleared
on a read of the status register only if the error condition has subsided.
LT = 1 indicates that the local low or high temperature has been exceeded. This bit is cleared on a
read of the status register only if the error condition has subsided.
R2T
OOL
R2T = 1 indicates that the Remote 2 low or high temperature has been exceeded. This bit is cleared
on a read of the status register only if the error condition has subsided.
OOL = 1 indicates that an out−of−limit event has been latched in Status Register 2. This bit is a logic-
al OR of all status bits in Status Register 2 (0x42). Software can test this bit in isolation to determine
whether any of the voltage, temperature, or fan speed readings represented by Status Register 2 are
out−of−limit, which eliminates the need to read Status Register 2 during every interrupt or polling
cycle.
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NCT7491
Table 66. REGISTER 0x42 − Interrupt Status Register 2 (Power−On Default = 0x00)
Bit
Name
R/W
Description
<0>
12 V
R
A 1 indicates that the 12 V high or low limit has been exceeded. This bit is cleared on a read of the
status register only if the error condition has subsided.
<1>
OOL
R
OOL = 1 indicates that an out−of−limit event has been latched in Status Register 3 (0x43). This bit is a
logical OR of all status bits in Status Register 3 Software can test this bit in isolation to determine
whether any of the voltage, temperature, or fan speed readings represented by Status Register 3 are
out−of−limit, which eliminates the need to read Status Register 3 during every interrupt or polling cycle.
<2>
<3>
<4>
<5>
FAN1
FAN2
FAN3
FAN4
R
R
R
R
FAN1 = 1 indicates that Fan 1 has dropped below minimum speed or has stalled. This bit is not set
when the PWM 1 output is off.
FAN2 = 1 indicates that Fan 2 has dropped below minimum speed or has stalled. This bit is not set
when the PWM 2 output is off.
FAN3 = 1 indicates that Fan 3 has dropped below minimum speed or has stalled. This bit is not set
when the PWM 3 output is off.
When Pin 14 on the QSOP package, Pin 11 on the QFN package is programmed as a TACH4 input,
FAN4 = 1 indicates that Fan 4 has dropped below minimum speed or has stalled. This bit is not set
when the PWM3 output is off.
<6>
<7>
D1
D2
R
R
D1 = 1 indicates either an open or short circuit on the Thermal Diode 1 inputs.
D2 = 1 indicates either an open or short circuit on the Thermal Diode 2 inputs.
Table 67. REGISTER 0x43 − Interrupt Status Register 3 (Power−On Default = 0x00)
Bit
Name
R/W
Description
<0>
PECI0
R
A logic 1 indicates that the PECI high or low limit has been exceeded by the PECI value from PECI client
address 0x30. This bit is cleared on a read of the status register only if the error condition has subsided.
<1>
Data
R
A logic 1 indicates that valid PECI data cannot be obtained for the processor and a specified error code
has been recorded.
<2>
<3>
Comm
OVT
R
R
A logic 1 indicates that there is a communications error (e.g. invalid FCS) on the PECI interface.
OVT = 1 indicates that one of the THERM over temperature limits has been exceeded. This bit is cleared
on a read of the status register when the temperature drops below THERM − T
.
HYST
<6:4>
DAT
R
If a DATA error occurs then bits <6:4> indicate the error type
<000> = General sensor error (0x8000)
<001> = Sensor underflow (0x8002)
<010> = Sensor overflow (0x8003)
<111> = Other
<7>
OOL3
R
OOL3 = 1 indicates that an out−of−limit event has been latched in Status Register 4 (0x81). This bit is a
logical OR of all status bits in Status Register 4 Software can test this bit in isolation to determine wheth-
er any of the voltage, temperature, or fan speed readings represented by Status Register 4 are out−of−
limit, which eliminates the need to read Status Register 4 during every interrupt or polling cycle.
Table 68. VOLTAGE LIMIT REGISTERS (Note 20)
Register Address
0x44
R/W
R/W
R/W
R/W
R/W
R/W
R/W
R/W
R/W
R/W
R/W
Description (Note 21)
2.5 V low limit.
Power−On Default
0x00
0xFF
0x00
0xFF
0x00
0xFF
0x00
0xFF
0x00
0xFF
0x45
2.5 V high limit.
0x46
V
V
V
V
low limit.
CCP
CCP
0x47
high limit.
0x48
low limit.
CC
CC
0x49
high limit.
0x4A
5 V low limit.
5 V high limit.
12 V low limit.
12 V high limit.
0x4B
0x4C
0x4D
20.Setting the Configuration Register 1 lock bit has no effect on these registers.
21.High limits: An interrupt is generated when a value exceeds its high limit (> comparison). Low limits: An interrupt is generated when a value
is equal to or below its low limit ( comparison).
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NCT7491
Table 69. TEMPERATURE LIMIT REGISTERS (Note 22)
Register Address
R/W
R/W
R/W
R/W
R/W
R/W
R/W
Description (Note 23)
Power−On Default
0x4E
0x4F
0x50
0x51
0x52
0x53
Remote 1 temperature low limit.
Remote 1 temperature high limit.
Local temperature low limit.
0x81
0x7F
0x81
0x7F
0x81
0x7F
Local temperature high limit.
Remote 2 temperature low limit.
Remote 2 temperature high limit.
22.Exceeding any of these temperature limits by 1°C causes the appropriate status bit to be set in the interrupt status register. Setting the
Configuration Register 1 lock bit has no effect on these registers.
23.High limits: An interrupt is generated when a value exceeds its high limit (> comparison). Low limits: An interrupt is generated when a value
is equal to or below its low limit (≤ comparison).
Table 70. FAN TACHOMETER LIMIT REGISTERS (Note 24)
Register Address
R/W
R/W
R/W
R/W
R/W
R/W
R/W
R/W
R/W
Description
TACH1 minimum low byte.
Power−On Default
0x54
0x55
0x56
0x57
0x58
0x59
0x5A
0x5B
0xFF
0xFF
0xFF
0xFF
0xFF
0xFF
0xFF
0xFF
TACH1 minimum high byte
TACH2 minimum low byte.
TACH2 minimum high byte.
TACH3 minimum low byte.
TACH3 minimum high byte.
TACH4 minimum low byte.
TACH4 minimum high byte.
24.Exceeding any of the TACH limit registers by 1 indicates that the fan is running too slowly or has stalled. The appropriate status bit is set
in Interrupt Status Register 2 to indicate the fan failure.
Table 71. PWM CONFIGURATION REGISTERS
Register Address
R/W
R/W
R/W
R/W
R/W
R/W
Description
Power−On Default
0x02
0x5C
0x5D
0x5E
PWM1 configuration.
PWM2 configuration.
PWM3 configuration.
Description
0x02
0x02
Bit
Name
SPIN
<2:0>
These bits control the startup timeout for PWMx. The PWM output stays high until two valid TACH
rising edges are seen from the fan. If there is not a valid TACH signal during the fan TACH meas-
urement directly after the fan startup timeout period, then the TACH measurement reads 0xFFFF
and Status Register 2 reflects the fan fault. If the TACH minimum high and low bytes contain
0xFFFF or 0x0000, then the Status Register 2 bit is not set, even if the fan has not started.
000 = No startup timeout
001 = 100 ms
010 = 250 ms (default)
011 = 400 ms
100 = 667 ms
101 = 1 sec
110 = 2 sec
111 = 4 sec
<3>
<4>
Reserved
INV
R/W
This bit inverts the PWM output. The default is 0, which corresponds to a logic high output for
100% duty cycle. Setting this bit to 1 inverts the PWM output, so 100% duty cycle corresponds to
a logic low output.
<7:5>
Reserved
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Table 72. TEMP TRANGE/PWM FREQUENCY REGISTERS
Register Address
R/W
R/W
R/W
R/W
R/W
R/W
Description
/PWM1 frequency.
Power−On Default
0xC3
0x5F
0x60
0x61
Remote 1 T
RANGE
Local temperature T
/PWM2 frequency.
0xC3
0xC3
RANGE
Remote 2 T
/PWM3 frequency.
RANGE
Bit
Name
Description
<2:0>
FREQ
These bits control the PWMx frequency (only apply when PWM channel is in low frequency
mode).
000 = 11.0 Hz
001 = 14.7 Hz
010 = 22.1 Hz
011 = 29.4 Hz (default)
100 = 35.3 Hz
101 = 44.1 Hz
110 = 58.8 Hz
111 = 88.2 Hz
<3>
HF/LF
R/W
R/W
HF/LF = 1, High frequency PWM mode is enabled for PWMx.
HF/LF = 0, Low frequency PWM mode is enabled for PWMx.
<7:4>
RANGE
These bits determine the PWM duty cycle vs. the temperature range for automatic fan control.
0000 = 2°C
0001 = 2.5°C
0010 = 3.33°C
0011 = 4°C
0100 = 5°C
0101 = 6.67°C
0110 = 8°C
0111 = 10°C
1000 = 13.33°C
1001 = 16°C
1010 = 20°C
1011 = 26.67°C
1100 = 32°C (default)
1101 = 40°C
1110 = 53.33°C
1111 = 80°C
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NCT7491
Table 73. REGISTER 0x62 − Enhanced Acoustics Register 1 (Power−On Default = 0x20)
Bit
Name
R/W
Description
<2:0>
ACOU
R/W
These bits define the maximum rate of change of the PWM1 output. Instead of the fan speed jumping
instantaneously to its newly determined speed, it ramps gracefully at the rate determined by these bits.
This feature ultimately enhances the acoustics of the fan.
Time Slot Increase
000 = 1
Time for 0% to 100%
37.5 sec
18.8 sec
12.5 sec
7.5 sec
001 = 2
010 = 3
011 = 4
100 = 8
4.7 sec
101 = 12
110 = 24
111 = 48
3.1 sec
1.6 sec
0.8 sec
<3>
<4>
EN1
R/W
R/W
When this bit is 1, smoothing is enabled on PWM1 output.
SYNC
SYNC = 1 synchronizes fan speed measurements on TACH2, TACH3, and TACH4 to PWM3. This
allows up to three fans to be driven from PWM3 output and their speeds to be measured.
SYNC = 0 synchronizes only TACH3 and TACH4 to PWM3 output.
<5>
<6>
<7>
MIN1
MIN2
MIN3
R/W
R/W
R/W
When the NCT7491 is in automatic fan control mode, this bit defines whether PWM1 is off (0% duty
cycle) or at PWM1 minimum duty cycle when the controlling temperature is below its T
value.
– hysteresis
MIN
0 = 0% duty cycle below T
– hysteresis.
MIN
1 = PWM1 minimum duty cycle below T
– hysteresis.
MIN
When the NCT7491 is in automatic fan speed control mode, this bit defines whether PWM2 is off (0%
duty cycle) or at PWM2 minimum duty cycle when the controlling temperature is below its T
teresis value.
– hys-
MIN
0 = 0% duty cycle below T
– hysteresis.
MIN
1 = PWM 2 minimum duty cycle below T
– hysteresis.
MIN
When the NCT7491 is in automatic fan speed control mode, this bit defines whether PWM3 is off (0%
duty cycle) or at PWM3 minimum duty cycle when the controlling temperature is below its T
teresis value.
– hys-
MIN
0 = 0% duty cycle below T
– hysteresis.
MIN
1 = PWM3 minimum duty cycle below T
– hysteresis.
MIN
Table 74. REGISTER 0x63 − Enhanced Acoustics Register 2 (Power−On Default = 0x00)
Bit
Name
R/W (Note 25)
Description
<2:0>
ACOU3
R/W
These bits define the maximum rate of change of the PWM3 output. Instead of the fan speed
jumping instantaneously to its newly determined speed, it ramps gracefully at the rate determ-
ined by these bits. This feature ultimately enhances the acoustics of the fan.
Time Slot Increase
000 = 1
Time for 0% to 100%
37.5 sec
18.8 sec
12.5 sec
7.5 sec
001 = 2
010 = 3
011 = 4
100 = 8
4.7 sec
101 = 12
110 = 24
111 = 48
3.1 sec
1.6 sec
0.8 sec
< 3 >
EN3
R/W
When this bit is 1, smoothing is enabled on the PWM3 output.
25.These registers become read−only when the NCT7491 is in automatic fan control mode.
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NCT7491
Table 74. REGISTER 0x63 − Enhanced Acoustics Register 2 (Power−On Default = 0x00)
Bit
Name
R/W (Note 25)
Description
<6:4>
ACOU2
R/W
These bits define the maximum rate of change of the PWM2 output. Instead of the fan speed
jumping instantaneously to its newly determined speed, it ramps gracefully at the rate determ-
ined by these bits. This feature ultimately enhances the acoustics of the fan.
Time Slot Increase
000 = 1
Time for 0% to 100%
37.5 sec
18.8 sec
12.5 sec
7.5 sec
001 = 2
010 = 3
011 = 4
100 = 8
4.7 sec
101 = 12
110 = 24
111 = 48
3.1 sec
1.6 sec
0.8 sec
<7>
EN2
R/W
When this bit is 1, smoothing is enabled on the PWM2 output.
25.These registers become read−only when the NCT7491 is in automatic fan control mode.
Table 75. PWM MINIMUM DUTY CYCLE REGISTERS
Register Address
R/W (Note 26)
R/W
Description
PWM1 minimum duty cycle.
PWM2 minimum duty cycle.
PWM3 minimum duty cycle.
Power−On Default
0x80 (50% duty cycle)
0x80 (50% duty cycle)
0x80 (50% duty cycle)
0x64
0x65
0x66
R/W
R/W
Bit
<7:0>
Name
R/W (Note 26)
R/W
Description
PWM duty cycle
These bits define the PWM
duty cycle for PWMx.
MIN
0x00 = 0% duty cycle (fan off).
0x40 = 25% duty cycle.
0x80 = 50% duty cycle.
0xFF = 100% duty cycle (fan full speed).
26.These registers become read−only when the NCT7491 is in automatic fan control mode.
Table 76. TMIN REGISTERS (Note 27)
Register Address
R/W
R/W
R/W
R/W
Description
Power−On Default
0x5A (90°C)
0x67
0x68
0x69
Remote 1 Temperature T
.
MIN
Local Temperature T
.
0x5A (90°C)
MIN
Remote 2 Temperature T
.
0x5A (90°C)
MIN
27.These are the T
registers for each temperature channel. When the temperature measured exceeds T , the appropriate fan runs at
MIN
MIN
minimum speed and increases with temperature according to T
.
RANGE
Table 77. THERM LIMIT REGISTERS (Note 28)
Register Address
R/W
R/W
R/W
R/W
Description
Power−On Default
0x64 (100°C)
0x6A
0x6B
0x6C
Remote 1 THERM limit.
Local THERM limit.
0x64 (100°C)
Remote 2 THERM limit.
0x64 (100°C)
28.If any temperature measured exceeds its THERM limit, all PWM outputs drive their fans at 100% duty cycle. This is a fail−safe mechanism
incorporated to cool the system in the event of a critical over temperature. It also ensures some level of cooling in the event that software
or hardware locks up. If set to 0x80, this feature is disabled. The PWM output remains at 100% until the temperature drops below THERM
limit − hysteresis. If the THERM pin is programmed as an output, exceeding these limits by 0.25°C can cause the THERM pin to assert low
as an output.
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NCT7491
Table 78. TEMPERATURE/TMIN HYSTERESIS REGISTERS (Note 29)
Register Address
0x6D
R/W
R/W
Description
Power−On Default
Remote 1 and Local Temperature hysteresis.
0x44
<3:0>
HYSL
Local Temperature hysteresis. 0°C to 15°C of hys-
teresis can be applied to the Local temperature
AFC control loops.
<7:4>
HYSR1
Remote 1 Temperature hysteresis. 0°C to 15°C of
hysteresis can be applied to the Remote 1 Temper-
ature AFC control loops.
0x6E
R/W
PECI and Remote 2 Temperature hysteresis.
0x44
<3:0>
HYSP
PECI Temperature hysteresis. 0°C to 15°C of hys-
teresis can be applied to the PECI AFC control
loops.
<7:4>
HYSR2
Remote 2 Temperature hysteresis. 0°C to 15°C of
hysteresis can be applied to the Local Temperature
AFC control loops.
29.Each 4−bit value controls the amount of temperature hysteresis applied to a particular temperature channel. Once the temperature for that
channel falls below its T value, the fan remains running at PWM duty cycle until the temperature = T
– hysteresis. Up to 15°C of
MIN
MIN
MIN
hysteresis can be assigned to any temperature channel. The hysteresis value chosen also applies to that temperature channel, if its THERM
limit is exceeded. The PWM output being controlled goes to 100%, if the THERM limit is exceeded and remains at 100% until the temperature
drops below THERM – hysteresis. For acoustic reasons, it is recommended that the hysteresis value not be programmed less than 4°C.
Setting the hysteresis value lower than 4°C causes the fan to switch on and off regularly when the temperature is close to T
.
MIN
Table 79. REGISTER 0x6F − XNOR Tree Test Enable (Power−On Default = 0x00)
Register Address
R/W (Note 30)
Description
<0>
XEN
If the XEN bit is set to 1, the device enters the XNOR tree test mode. Clearing
the bit removes the device from the XNOR tree test mode.
<7:1>
Reserved
Unused. Do not write to these bits.
30.This register becomes read−only when the Configuration Register 1 lock bit is set to 1. Any further attempts to write to this register have no effect.
Table 80. REMOTE 1 TEMPERATURE OFFSET (Note 31)
Register Address
0x70
R/W (Note 31)
R/W
Description
Power−On Default
Remote 1 temperature offset.
0x00
<7:0>
R/W
Allows a temperature offset to be automatically ap-
plied to the remote temperature 1 channel meas-
urement. Bit 1 of 0x7C (Configuration Register 5)
determines the range and resolution of this register.
31.This register becomes read−only when the Configuration Register 1 lock bit is set to 1. Any further attempts to write to this register have no effect.
Table 81. LOCAL TEMPERATURE OFFSET (Note 32)
Register Address
0x71
Description
Local temperature offset.
Power−On Default
R/W (Note 32)
R/W
0x00
<7:0>
R/W
Allows a temperature offset to be automatically ap-
plied to the local temperature measurement. Bit 1 of
0x7C (Configuration Register 5) determines the
range and resolution of this register.
32.This register becomes read−only when the Configuration Register 1 lock bit is set to 1. Any further attempts to write to this register have no effect.
Table 82. REMOTE 2 TEMPERATURE OFFSET (Note 33)
Register Address
0x72
Description
Power−On Default
R/W (Note 33)
R/W
Remote 2 temperature offset.
0x00
<7:0>
R/W
Allows a temperature offset to be automatically ap-
plied to the remote temperature 2 channel meas-
urement. Bit 1 of 0x7C (Configuration Register 5)
determines the range and resolution of this register.
33.This register becomes read−only when the Configuration Register 1 lock bit is set to 1. Any further attempts to write to this register have no effect.
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NCT7491
Table 83. REGISTER 0x73 − Configuration Register 2 (Power−On Default = 0x00) (Note 34)
Bit
0
Name
Description
R/W (Note 34)
Reserved
Reserved
ABS/REL
R
R
1
2
R/W
0 = PECI uses relative values for fan control
1 = PECI uses absolute value for fan control
3
4
VAVG
TAVG
FQ
R/W
R/W
R/W
VAVG = 1 indicates that averaging on the voltage measurements is turned off. This
allows measurements on each channel to be made much faster.
TAVG = 1 indicates that averaging on the temperature measurements is turned off.
This allows measurements on each channel to be made much faster.
<6:5>
Sets the fault queue length:
<00> = 1 event
<01> = 2 events
<10> = 3 events
<11> = 4 events
7
Shutdown
R/W
34.This register becomes read−only when the Configuration Register 1 lock bit is set to 1. Any further attempts to write to this register have no effect.
Table 84. REGISTER 0x74 − Interrupt Mask Register 1 (Power−On Default = 0x00)
Bit
0
Name
R/W
R/W
R/W
R/W
R/W
R/W
R/W
R/W
R
Description
2.5 V
2.5 V = 1, masks SMBALERT for out−of−limit conditions on the 2.5 V channel.
1
V
CCP
V
V
= 1 masks SMBALERT for out−of−limit conditions on the V
channel.
CCP
CCP
2
V
CC
= 1 masks SMBALERT for out−of−limit conditions on the V channel.
CC CC
3
5 V
RIT
LT
5 V = 1 masks SMBALERT for out−of−limit conditions on the 5 V channel.
RIT = 1 masks SMBALERT for out−of−limit conditions on the Remote 1 Temperature channel.
LT = 1 masks SMBALERT for out−of−limit conditions on the Local Temperature channel.
R2T = 1 masks SMBALERT for out−of−limit conditions on the Remote 2 Temperature channel.
Reserved
4
5
6
R2T
7
Table 85. REGISTER 0x75 − Interrupt Mask Register 2 (Power−On Default = 0x00)
Bit
0
Name
R/W
R/W
R
Description
12 V = 1, masks SMBALERT for out−of−limit conditions on the 12 V channel.
Reserved
12 V
1
2
FAN1
FAN2
FAN3
FAN4
D1
R/W
R/W
R/W
R/W
R/W
R/W
FAN1 = 1 masks SMBALERT for a Fan 1 fault.
3
FAN2 = 1 masks SMBALERT for a Fan 2 fault.
4
FAN3 = 1 masks SMBALERT for a Fan 3 fault.
5
FAN4 = 1 masks SMBALERT for a Fan 4 fault.
6
D1 = 1 masks SMBALERT for a diode open or short on a Remote 1 channel.
D2 = 1 masks SMBALERT for a diode open or short on a Remote 2 channel.
7
D2
Table 86. REGISTER 0x76 − Extended Resolution Register 1 (Note 35) (Power−On Default = 0x00)
Bit
Name
R/W
R
Description
<1:0>
<3:2>
<5:4>
<7:6>
2.5 V
2.5 V LSBs. Holds the 2 LSBs of the 10−bit 2.5 V measurement.
V
CCP
R
V
V
LSBs. Holds the 2 LSBs of the 10−bit V
measurement.
CCP
CCP
V
CC
R
LSBs. Holds the 2 LSBs of the 10−bit V measurement.
CC CC
5 V
R
5 V LSBs. Holds the 2 LSBs of the 10−bit 5 V measurement.
35.If this register is read, this register and the registers holding the MSB of each reading are frozen until read.
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Table 87. REGISTER 0x77 − Extended Resolution Register 2 (Note 36) (Power−On Default = 0x00)
Bit
Name
12 V
R/W
R
Description
<1:0>
<3:2>
<5:4>
<7:6>
12 V LSBs. Holds the 2 LSBs of the 10−bit 12 V measurement.
TDM1
LTMP
TDM2
R
Remote 1 Temperature LSBs. Holds the 2 LSBs of the 10−bit Remote 1 temperature measurement.
Local Temperature LSBs. Holds the 2 LSBs of the 10−bit local temperature measurement.
Remote 2 Temperature LSBs. Holds the 2 LSBs of the 10−bit Remote 2 temperature measurement.
R
R
36.If this register is read, this register and the registers holding the MSB of each reading are frozen until read.
Table 88. REGISTER 0x78 − Configuration Register 3 (Power−On Default = 0x00)
R/W
(Note 37)
Bit
Name
Description
<0>
ALERT
R/W
ALERT = 1, Pin 10 on the QSOP package, Pin 7 on the QFN package (PWM2/SMBALERT) is
configured as an SMBALERT interrupt output to indicate out−of−limit error conditions.
ALERT = 0, Pin 10 on the QSOP package, Pin 7 on the QFN package (PWM2/SMBALERT ) is
configured as the PWM2 output.
<1>
THERM /
2.5 V
R/W
THERM = 1 enables THERM functionality on Pin 22 on the QSOP package, Pin 19 on the QFN
package
<2>
<3>
Reserved
FAST
R
R/W
FAST = 1 enables fast TACH measurements on all channels. This increases the TACH measure-
ment rate from once per second to once every 250 ms (4 x).
<4>
<5>
<6>
<7>
DC1
DC2
DC3
DC4
R/W
R/W
R/W
R/W
DC1 = 1 enables TACH measurements to be continuously made on TACH1. Fans must be driven
by dc. Setting this bit prevents pulse stretching because it is not required for dc−driven motors.
DC2 = 1 enables TACH measurements to be continuously made on TACH2. Fans must be driven
by dc. Setting this bit prevents pulse stretching because it is not required for dc−driven motors.
DC3 = 1 enables TACH measurements to be continuously made on TACH3. Setting this bit pre-
vents pulse stretching because it is not required for dc−driven motors.
DC4 = 1 enables TACH measurements to be continuously made on TACH4. Setting this bit pre-
vents pulse stretching because it is not required for dc−driven motors.
37.Bits <3:0> of this register become read−only when the Configuration Register 1 lock bit is set to 1. Any further attempts to write to bits <3:0>
have no effect.
Table 89. REGISTER 0x79 − THERM Timer Value Register (Power−On Default = 0x00)
Bit
Name
R/W
Description
<7:1>
TMR
R
Times how long THERM input is asserted. These seven bits read zero until the THERM assertion time
exceeds 45.52 ms.
<0>
ASRT/
TMR0
R
This bit is set high on the assertion of the THERM input and is cleared on read. If the THERM asser-
tion time exceeds 45.52 ms, this bit is set and becomes the LSB of the 8−bit TMR reading. This allows
THERM assertion times from 45.52 ms to 5.82 sec to be reported back with a resolution of 22.76 ms.
Table 90. REGISTER 0x7A − THERM Timer Limit Register (Power−On Default = 0xFF)
Bit
Name
R/W
Description
<7:0>
LIMT
R/W
Sets maximum THERM assertion length allowed before an interrupt is generated. This is an
8−bit limit with a resolution of 22.76 ms allowing THERM assertion limits of 45.52 ms to 5.82 s
to be programmed. If the THERM assertion time exceeds this limit, Bit 5 (F4P) of Interrupt
Status Register 2 (Reg. 0x42) is set. If the limit value is 0x00, an interrupt is generated immedi-
ately on the assertion of the THERM input. If THERM is configured as an output the THERM
timer limit should be set to 0xFF to avoid unwanted alerts from being generated.
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Table 91. REGISTER 0x7B − TACH Pulses per Revolution Register (Power−On Default = 0x55)
Bit
Name
R/W
Description
<1:0>
FAN1
R/W
Sets number of pulses to be counted when measuring Fan 1 speed. Can be used to determine fan
pulses per revolution for unknown fan type.
Pulses Counted
00 = 1
01 = 2 (default)
10 = 3
11 = 4
<3:2>
<5:4>
<7:6>
FAN2
FAN3
FAN4
R/W
R/W
R/W
Sets number of pulses to be counted when measuring Fan 2 speed. Can be used to determine fan
pulses per revolution for unknown fan type.
Pulses Counted
00 = 1
01 = 2 (default)
10 = 3
11 = 4
Sets number of pulses to be counted when measuring Fan 3 speed. Can be used to determine fan
pulses per revolution for unknown fan type.
Pulses Counted
00 = 1
01 = 2 (default)
10 = 3
11 = 4
Sets number of pulses to be counted when measuring Fan 4 speed. Can be used to determine fan
pulses per revolution for unknown fan type.
Pulses Counted
00 = 1
01 = 2 (default)
10 = 3
11 = 4
Table 92. REGISTER 0x7C − Configuration Register 5 (Power−On Default = 0x05)
R/W
(Note 38)
Bit
Name
Description
<0>
2sC
R/W
2sC = 1 sets the temperature range to the twos complement temperature range.
2sC = 0 changes the temperature range to the offset 64 temperature range. When this bit is
changed, the NCT7491 interprets all relevant temperature register values as defined by this bit.
<1>
TempOffset
R/W
R/W
TempOffset = 0 sets offset range to −63C to +64C with 0.5°C resolution.
TempOffset = 1 sets offset range to −63°C to +127°C with 1°C resolution.
These settings apply to registers 0x70, 0x71, and 0x72 (Remote 1, Internal and Remote2 Tem-
perature offset registers. Note: PECI offset is always 1°C resolution.)
<3:2>
Pin19
00 = Pin 19 is SMBALERT
Function
01 = Pin 19 is THERM
10 = Pin 19 is GPIO3
11 = reserved
Note: Pin 19 refers to the QSOP package. The equivalent pin on the QFN package is pin 16.
38.This register becomes read−only when the Configuration Register 1 lock bit is set to 1. Any further attempts to write to this register have
no effect.
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Table 92. REGISTER 0x7C − Configuration Register 5 (Power−On Default = 0x05)
R/W
(Note 38)
Bit
Name
Description
<4>
PECI
CONTROL
R/W
PECI = 1 enables THERM assertions when the PECI temperature read is higher than the PECI
T
T
limit and the THERM pin is bidirectional. If THERM is configured as an output the
CONTROL
THERM timer limit (register 0x7A) should be set to 0xFF to avoid unwanted alerts from being
generated.
PECI = 0 indicates that the THERM pin is configured as a timer input only. Can also be disabled
by writing −128°C to the relevant PECI T
limit register.
CONTROL
<5>
R1 THERM
R/W
R1 = 1 enables THERM assertions when the Remote 1 temperature read is higher than the
Remote 1 THERM limit and the THERM pin is bidirectional. If THERM is configured as an out-
put the THERM timer limit (register 0x7A) should be set to 0xFF to avoid unwanted alerts from
being generated.
R1 = 0 indicatesthat the THERM pin is configured as a timer input only.
can also be disabled by writing one of the below values to the Remote 1 THERM limit register
(0x6A): Writing −64°C in offset 64 mode.
Writing −128°C in twos complement mode.
<6>
<7>
Local
THERM
R/W
R/W
Local = 1 enables THERM assertions when the Local temperature read is higher than the Local
THERM limit and the THERM pin is bidirectional. If THERM is configured as an output the
THERM timer limit (register 0x7A) should be set to 0xFF to avoid unwanted alerts from being
generated.
can also be disabled by writing one of the below values to the Remote 1 THERM limit register
(0x6B): Writing −64°C in offset 64 mode.
Writing −128°C in twos complement mode.
R2 THERM
R2 = 1 enables THERM assertions when the Remote 2 temperature read is higher than the
Remote 2 THERM limit and the THERM pin is bidirectional. If THERM is configured as an out-
put the THERM timer limit (register 0x7A) should be set to 0xFF to avoid unwanted alerts from
being generated.
can also be disabled by writing one of the below values to the Remote 1 THERM limit register
(0x6C): Writing −64°C in offset 64 mode.
Writing −128°C in twos complement mode.
38.This register becomes read−only when the Configuration Register 1 lock bit is set to 1. Any further attempts to write to this register have
no effect.
Table 93. REGISTER 0x7D − Configuration Register 4 (Power−On Default = 0x00)
R/W
(Note 39)
Bit
Name
Description
<1:0>
PIN14FUNC
R/W
These bits set the functionality of Pin 14:
00 = TACH4 (default)
01 = THERM
10 = SMBALERT
11 = RESERVED
Note: Pin 14 refers to the QSOP package. The equivalent pin on the QFN package is pin 11.
<2>
THERM
Disable
R/W
THERM Disable = 0 enables THERM overtemperature output assuming THERM is correctly
configured (registers 0x78, 0x7C, 0x7D).
THERM Disable = 1 disables THERM overtemperature output on all channels.
THERM can also be disabled on any channel by:
Writing −64°C to the appropriate THERM temperature limit in offset 64 mode.
Writing −128°C to the appropriate THERM temperature limit in twos complement mode.
<3>
<4>
<5>
<6>
<7>
BpAtt Vtt
R/W
R/W
R/W
R/W
R/W
Bypass Vtt attenuator. When set, the measurement scale for this channel changes from 0 V
(0x00) to 2 V (0xFF).
BpAtt2.5 V
Bypass 2.5 V attenuator. When set, the measurement scale for this channel changes from 0 V
(0x00) to 2 V (0xFF).
BpAttV
Bypass V
attenuator. When set, the measurement scale for this channel changes from 0 V
CCP
CCP
(0x00) to 2 V (0xFF).
BpAtt5 V
Bypass 5 V attenuator. When set, the measurement scale for this channel changes from 0 V
(0x00) to 2 V (0xFF).
BpAtt12 V
Bypass 12 V attenuator. When set, the measurement scale for this channel changes from 0 V
(0x00) to 2 V (0xFF).
39.This register becomes read−only when the Configuration Register 1 lock bit is set to 1. Any further attempts to write to this register have no
effect.
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Table 94. REGISTER 0x7E − Interrupt Status 5 (Power−On Default = 0x00)
Bit
Name
PUSH0
PUSH1
PUSH2
PUSH3
OVT_P0
OVT_P1
OVT_P2
OVT_P3
R/W
R
Description
Logic 1 indicates ALERT assertion for Push0 temperature
Logic 1 indicates ALERT assertion for Push1 temperature
Logic 1 indicates ALERT assertion for Push2 temperature
Logic 1 indicates ALERT assertion for Push3 temperature
Logic 1 indicates THERM assertion for Push0 temperature
Logic 1 indicates THERM assertion for Push1 temperature
Logic 1 indicates THERM assertion for Push2 temperature
Logic 1 indicates THERM assertion for Push3 temperature
<0>
<1>
<2>
<3>
<4>
<5>
<6>
<7>
R
R
R
R
R
R
R
Table 95. REGISTER 0x7F − Interrupt Mask 5 (Power−On Default = 0x00)
Bit
Name
PUSH0
R/W
R/W
R/W
R/W
R/W
R
Description
<0>
<1>
<2>
<3>
<4>
<5>
<6>
<7>
Logic 1 masks PUSH0 ALERT assertions
Logic 1 masks PUSH1 ALERT assertions
Logic 1 masks PUSH2 ALERT assertions
Logic 1 masks PUSH3 ALERT assertions
Reserved
PUSH1
PUSH2
PUSH3
Reserved
Reserved
Reserved
Reserved
R
Reserved
R
Reserved
R
Reserved
Table 96. REGISTER 0x80 − GPIO Register (Power−On Default = 0xCE )
Bit
<0>
<1>
Name
RES
R/W
Description
RESERVED
GPEN
1= GPIO1 enabled on pin 5, GPIO2 enabled on pin 6
0 = GPIO1 and GPIO2 are disabled
This bit only has effect if the SMBus master port is disabled (0xB5 <0> =0)
<2>
<3>
GPIO2
GPIO1
R/W
R/W
If GPIO2 is set to input, this register reflects the state of the pin. If GPIO2 is configured as
an output, writing to this register asserts the output high or low depending on the polarity.
If GPIO1 is set to input, this register reflects the state of the pin. If GPIO1 is configured as
an output, writing to this register asserts the output high or low depending on the polarity.
<4>
<5>
<6>
GPIO2 POL
GPIO1 POL
GPIO2 DIR
R/W
R/W
R/W
GPIO2 polarity bit. Set to 0 for active low. Set to1 for active high.
GPIO1 polarity bit. Set to 0 for active low. Set to1 for active high.
GPIO2 direction bit. Set to 1 for GPIO2 to act as an input, set to 0 for GPIO2 to act as an
output.
<7>
GPIO1 DIR
R/W
GPIO1 direction bit. Set to 1 for GPIO1 to act as an input, set to 0 for GPIO1 to act as an
output.
Table 97. REGISTER 0x81 − Interrupt Status Register 4 (Power−On Default = 0x00)
Bit
Name
PCC
R/W
R
Description
<0>
<1>
<2>
<3>
<4>
<5>
PECI Completion code interrupt
TTS
R
Logic 1 indicates that the THERM Timer limit has been exceeded.
GCOMM
PECI1
PECI2
PECI3
R
Logic 1 indicates a COMM error resulting from a Generic PECI instruction
R
A logic 1 indicates that the PECI high or low limit has been exceeded by the PECI1 value.
A logic 1 indicates that the PECI high or low limit has been exceeded by the PECI2 value.
A logic 1 indicates that the PECI high or low limit has been exceeded by the PECI3 value.
R
R
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Table 97. REGISTER 0x81 − Interrupt Status Register 4 (Power−On Default = 0x00)
Bit
Name
R/W
Description
<6>
SMBCNT
R
Logic 1 indicates that the byte count returned by the SMBus Master Block Read is too low. If the
PCH temperature only is required then the returned byte count should be 2 or greater. If DIMM
temperatures are being read from the PCH then the returned byte count should be 9 or greater.
<7>
V
TT
R
A logic 1 indicates that the V high or low limit has been exceeded. This bit is cleared on a read
of the status register only if the error condition has subsided.
TT
Table 98. REGISTER 0x82 − Interrupt Mask Register 3 (Power−On Default = 0x00)
Bit
<0>
<1>
Name
PECI0
DATA
R/W
R/W
R/W
Description
A logic 1 masks SMBALERT assertions for out−of−limit conditions on PECI0.
A logic 1 masks SMBALERT assertions for PECI Data errors. This also disables the fan over−ride
function for PECI errors.
<2>
COMM
R/W
A logic 1 masks SMBALERT assertions for PECI communications errors. This also disables the
fan over−ride function for PECI errors.
<3>
<6:4>
<7>
OVT
RES
R/W
R/W
R
OVT = 1 masks SMBALERT for over temperature THERM conditions.
Reserved
Reserved
NOTE: If the mask bits in register 0x82 are set it is also necessary to set the OOL mask bit in register 0x75 to ensure the SMBALERT
output is not asserted.
Table 99. REGISTER 0x83 − Interrupt Mask Register 4 (Power−On Default = 0x00)
Bit
Name
PCC
R/W
R/W
R/W
R/W
R/W
R/W
R/W
R/W
R/W
Description
<0>
<1>
<2>
<3>
<4>
<5>
<6>
<7>
Logic 1 masks ALERT assertions for PECI completion codes.
Logic 1 masks assertions for THERM Timer status bit
TTS
GCOMM
PECI1
PECI2
PECI3
SMBCNT
Logic 1 masks the GCOMM PECI status bit
A logic 1 masks ALERT assertions for out−of−limit conditions on PECI1.
A logic 1 masks ALERT assertions for out−of−limit conditions on PECI2.
A logic 1 masks ALERT assertions for out−of−limit conditions on PECI3.
Logic 1 masks ALERT assertions for incorrect byte count values returned by the Block Read command
V
TT
A logic 1 masks ALERT assertions for out−of−limit conditions on V .
TT
NOTE: If the mask bits in register 0x83 are set it is also necessary to set the OOL mask bit in register 0x82 to ensure the SMBALERT
output is not asserted.
Table 100. VTT LOW LIMIT REGISTER
Register Address
R/W
Description
Low Limit
Power−On Default
0x84
R/W
V
0x00
TT
Table 101. REGISTER 0x85 − GPIO Config2 (Power−On Default = 0x80)
Bit
<4:0>
<5>
Name
Reserved
GPIO3
R/W
Description
R/W
If GPIO3 is set to input, this bit reflects the state of the pin. If GPIO3 is configured as an
output, writing to this register asserts the output high or low depending on the polarity.
<6>
<7>
GPIO3 POL
GPIO3 DIR
R/W
R/W
GPIO3 polarity bit. Set to 0 for active low. Set to1 for active high.
GPIO3 direction bit. Set to 1 for GPIO3 to act as an input, set to 0 for GPIO3 to act as an
output, OOL must also be masked.
Table 102. VTT HIGH LIMIT REGISTER
Register Address
R/W
Description
High Limit
Power−On Default
0x86
R/W
V
0xFF
TT
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Table 103. REGISTER 0x87 − Configuration 9 (Power−On Default = 0x00)
Bit
Name
PWM1OFF
PWM2OFF
PWM3OFF
Reserved
D0V
R/W
R/W
R/W
R/W
R
Description
<0>
<1>
<2>
<3>
<4>
<5>
<6>
<7>
1= Disables PWM1
1= Disables PWM2
1 = Disables PWM3
R/W
R/W
R/W
R/W
1 = DIMM0 is populated, must be set to enable DIMM0 temperature to be written to CPU
1 = DIMM1 is populated, must be set to enable DIMM1 temperature to be written to CPU
1 = DIMM2 is populated, must be set to enable DIMM2 temperature to be written to CPU
1 = DIMM3 is populated, must be set to enable DIMM3 temperature to be written to CPU
D1V
D2V
D3V
Table 104. REGISTER 0x88 − PECI Configuration Register 2 (Power−On Default = 0x00)
Bit
<2:0>
<3>
Name
RES
R/W
R
Description
RESERVED
DOM3
R/W
CPU Domain Count information. Set to 0 indicates that CPU 4 associated with the PECI3 reading has
a single domain (Default). Set to 1 indicates that the system CPU4 contains two domains.
<4>
<5>
DOM2
DOM1
#CPU
R/W
R/W
R/W
CPU Domain Count information. Set to 0 indicates that CPU 3 associated with the PECI2 reading has
a single domain (Default). Set to 1 indicates that the system CPU3 contains two domains.
CPU Domain Count information. Set to 0 indicates that CPU 2 associated with the PECI1 reading has
a single domain (Default). Set to 1 indicates that the system CPU2 contains two domains.
<7:6>
CPU Count. These bits indicate the number of CPU’s in the system. That will provide PECI thermal
information to the NCT7491.
00 = 1 CPU
01 = 2 CPUs
10 = 3 CPUs
11 = 4 CPUs
Table 105. REGISTER 0x89 − Interrupt Status 7 (Power−On Default = 0x00)
Bit
Name
OVT0
R/W
R
Description
<0>
<1>
<2>
<3>
<4>
<5>
<6>
<7>
1 = PECI0 Tcontrol exceeded
1 = PECI1 Tcontrol exceeded
1 = PECI2 Tcontrol exceeded
1 = PECI3 Tcontrol exceeded
1 = Remote1 THERM exceeded
1 = Local THERM exceeded
1 = Remote2 THERM exceeded
OVT1
R
OVT2
R
OVT3
R
OVT_R1
OVT_LOC
OVT_R2
OOL11
R
R
R
R
1 indicates an out of limit condition in register 0xBB
Table 106. REGISTER 0x8A − PWM1 Source Control 1 (Power−On Default = 0x08)
Bit
Name
LOC
R/W
R/W
R/W
R/W
R/W
R/W
R/W
R/W
Description
<0>
<1>
<2>
<3>
<4>
<5>
<6>
<7>
Logic 1 enables Local temperature to control PWM1 in automatic fan control loop
Logic 1 enables Remote1 temperature to control PWM1 in automatic fan control loop
Logic 1 enables Remote2 temperature to control PWM1 in automatic fan control loop
Logic 1 enables PECI0 temperature to control PWM1 in automatic fan control loop
Logic 1 enables PECI1 temperature to control PWM1 in automatic fan control loop
Logic 1 enables PECI2 temperature to control PWM1 in automatic fan control loop
Logic 1 enables PECI3 temperature to control PWM1 in automatic fan control loop
REM1
REM2
PEC0
PEC1
PEC2
PEC3
Reserved
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Table 107. REGISTER 0x8B − PWM1 Source Control 2 (Power−On Default = 0x00)
Bit
Name
SMB0
SMB1
SMB2
SMB3
SMB4
SMB5
SMB6
SMB7
R/W
R/W
R/W
R/W
R/W
R/W
R/W
R/W
R/W
Description
<0>
<1>
<2>
<3>
<4>
<5>
<6>
<7>
Logic 1 enables SMBus Slave Device 0 to control PWM1 in automatic fan control loop
Logic 1 enables SMBus Slave Device 1 to control PWM1 in automatic fan control loop
Logic 1 enables SMBus Slave Device 2 to control PWM1 in automatic fan control loop
Logic 1 enables SMBus Slave Device 3 to control PWM1 in automatic fan control loop
Logic 1 enables SMBus Slave Device 4 to control PWM1 in automatic fan control loop
Logic 1 enables SMBus Slave Device 5 to control PWM1 in automatic fan control loop
Logic 1 enables SMBus Slave Device 6 to control PWM1 in automatic fan control loop
Logic 1 enables SMBus Slave Device 7 to control PWM1 in automatic fan control loop
Table 108. REGISTER 0x8C − PWM1 Source Control 3 (Power−On Default = 0x00)
Bit
Name
PUSH0
R/W
R/W
R/W
R/W
R/W
Description
<0>
<1>
<2>
<3>
<4>
<5>
<6>
<7>
Logic 1 enables Externally written temperature 0 to control PWM1 in automatic fan control loop
Logic 1 enables Externally written temperature 1 to control PWM1 in automatic fan control loop
Logic 1 enables Externally written temperature 2 to control PWM1 in automatic fan control loop
Logic 1 enables Externally written temperature 3 to control PWM1 in automatic fan control loop
PUSH1
PUSH2
PUSH3
Reserved
Reserved
Reserved
Reserved
Table 109. REGISTER 0x8D − PWM2 Source Control 1 (Power−On Default = 0x00)
Bit
Name
LOC
R/W
R/W
R/W
R/W
R/W
R/W
R/W
R/W
Description
<0>
<1>
<2>
<3>
<4>
<5>
<6>
<7>
Logic 1 enables Local temperature to control PWM2 in automatic fan control loop
Logic 1 enables Remote1 temperature to control PWM2 in automatic fan control loop
Logic 1 enables Remote2 temperature to control PWM2 in automatic fan control loop
Logic 1 enables PECI0 temperature to control PWM2 in automatic fan control loop
Logic 1 enables PECI1 temperature to control PWM2 in automatic fan control loop
Logic 1 enables PECI2 temperature to control PWM2 in automatic fan control loop
Logic 1 enables PECI3 temperature to control PWM2 in automatic fan control loop
REM1
REM2
PEC0
PEC1
PEC2
PEC3
Reserved
Table 110. REGISTER 0x8E − PWM2 Source Control 2 (Power−On Default = 0x00)
Bit
Name
SMB0
SMB1
SMB2
SMB3
SMB4
SMB5
SMB6
SMB7
R/W
R/W
R/W
R/W
R/W
R/W
R/W
R/W
R/W
Description
<0>
<1>
<2>
<3>
<4>
<5>
<6>
<7>
Logic 1 enables SMBus Slave Device 0 to control PWM2 in automatic fan control loop
Logic 1 enables SMBus Slave Device 1 to control PWM2 in automatic fan control loop
Logic 1 enables SMBus Slave Device 2 to control PWM2 in automatic fan control loop
Logic 1 enables SMBus Slave Device 3 to control PWM2 in automatic fan control loop
Logic 1 enables SMBus Slave Device 4 to control PWM2 in automatic fan control loop
Logic 1 enables SMBus Slave Device 5 to control PWM2 in automatic fan control loop
Logic 1 enables SMBus Slave Device 6 to control PWM2 in automatic fan control loop
Logic 1 enables SMBus Slave Device 7 to control PWM2 in automatic fan control loop
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NCT7491
Table 111. REGISTER 0x8F − PWM2 Source Control 3 (Power−On Default = 0x00)
Bit
Name
PUSH0
R/W
R/W
R/W
R/W
R/W
Description
<0>
<1>
<2>
<3>
<4>
<5>
<6>
<7>
Logic 1 enables Externally written temperature 0 to control PWM2 in automatic fan control loop
Logic 1 enables Externally written temperature 1 to control PWM2 in automatic fan control loop
Logic 1 enables Externally written temperature 2 to control PWM2 in automatic fan control loop
Logic 1 enables Externally written temperature 3 to control PWM2 in automatic fan control loop
PUSH1
PUSH2
PUSH3
Reserved
Reserved
Reserved
Reserved
Table 112. REGISTER 0x90 − PWM3 Source Control 1 (Power−On Default = 0x00)
Bit
Name
LOC
R/W
R/W
R/W
R/W
R/W
R/W
R/W
R/W
Description
<0>
<1>
<2>
<3>
<4>
<5>
<6>
<7>
Logic 1 enables Local temperature to control PWM3 in automatic fan control loop
Logic 1 enables Remote1 temperature to control PWM3 in automatic fan control loop
Logic 1 enables Remote2 temperature to control PWM3 in automatic fan control loop
Logic 1 enables PECI0 temperature to control PWM3 in automatic fan control loop
Logic 1 enables PECI1 temperature to control PWM3 in automatic fan control loop
Logic 1 enables PECI2 temperature to control PWM3 in automatic fan control loop
Logic 1 enables PECI3 temperature to control PWM3 in automatic fan control loop
REM1
REM2
PEC0
PEC1
PEC2
PEC3
Reserved
Table 113. REGISTER 0x91 − PWM3 Source Control 2 (Power−On Default = 0x00)
Bit
Name
SMB0
SMB1
SMB2
SMB3
SMB4
SMB5
SMB6
SMB7
R/W
R/W
R/W
R/W
R/W
R/W
R/W
R/W
R/W
Description
<0>
<1>
<2>
<3>
<4>
<5>
<6>
<7>
Logic 1 enables SMBus Slave Device 0 to control PWM3 in automatic fan control loop
Logic 1 enables SMBus Slave Device 1 to control PWM3 in automatic fan control loop
Logic 1 enables SMBus Slave Device 2 to control PWM3 in automatic fan control loop
Logic 1 enables SMBus Slave Device 3 to control PWM3 in automatic fan control loop
Logic 1 enables SMBus Slave Device 4 to control PWM3 in automatic fan control loop
Logic 1 enables SMBus Slave Device 5 to control PWM3 in automatic fan control loop
Logic 1 enables SMBus Slave Device 6 to control PWM3 in automatic fan control loop
Logic 1 enables SMBus Slave Device 7 to control PWM3 in automatic fan control loop
Table 114. REGISTER 0x92 − PWM3 Source Control 3 (Power−On Default = 0x00)
Bit
Name
PUSH0
R/W
R/W
R/W
R/W
R/W
Description
<0>
<1>
<2>
<3>
<4>
<5>
<6>
<7>
Logic 1 enables Externally written temperature 0 to control PWM3 in automatic fan control loop
Logic 1 enables Externally written temperature 1 to control PWM3 in automatic fan control loop
Logic 1 enables Externally written temperature 2 to control PWM3 in automatic fan control loop
Logic 1 enables Externally written temperature 3 to control PWM3 in automatic fan control loop
PUSH1
PUSH2
PUSH3
Reserved
Reserved
Reserved
Reserved
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NCT7491
Table 115. DEVICE ID REGISTER
Register Address
R/W
Read
Description
Device Revision
Power−On Default
0x93
Table 116. PECI OFFSET REGISTERS
Register Address
R/W
R/W
R/W
R/W
R/W
Description
Power−On Default
0x94
0x95
0x96
0x97
PECI0 Offset
PECI1 Offset
PECI2 Offset
PECI3 Offset
0x00
0x00
0x00
0x00
Table 117. SMBus MASTER ADDRESS TABLE
Register Address
0x98
R/W
R/W
R/W
R/W
R/W
R/W
R/W
R/W
R/W
R/W
R/W
R/W
R/W
R/W
R/W
R/W
R/W
Description
Device 0 (PCH) SMBus Address
Default
0x00
0x40
0x00
0x00
0x00
0x00
0x00
0x00
0x00
0x00
0x00
0x00
0x00
0x00
0x00
0x00
0x99
Device 0 (PCH) Block Read command code
Device 1 SMBus Address
0x9A
0x9B
Device 1 Temperature Address Pointer
Device 2 SMBus Address
0x9C
0x9D
Device 2 Temperature Address Pointer
Device 3 SMBus Address
0x9E
0x9F
Device 3 Temperature Address Pointer
Device 4 SMBus Address
0xA0
0xA1
Device 4 Temperature Address Pointer
Device 5 SMBus Address
0xA2
0xA3
Device 5 Temperature Address Pointer
Device 6 SMBus Address
0xA4
0xA5
Device 6 Temperature Address Pointer
Device 7 SMBus Address
0xA6
0xA7
Device 7 Temperature Address Pointer
Table 118. SMBus MASTER TEMPERATURE VALUES
Register Address
0xA8
R/W
R/W
R/W
R/W
R/W
R/W
R/W
R/W
R/W
Description
SMBus Device 0 (PCH) Temperature
Default
0x80
0x80
0x80
0x80
0x80
0x80
0x80
0x80
0xA9
SMBus Device 1 (DIMM0) Temperature
SMBus Device 2 (DIMM1) Temperature
SMBus Device 3 (DIMM2) Temperature
SMBus Device 4 (DIMM3) Temperature
SMBus Device 5 Temperature
0xAA
0xAB
0xAC
0xAD
0xAE
SMBus Device 6 Temperature
0xAF
SMBus Device 7 Temperature
Table 119. Register 0xB0 − SMBus Master Configuration 1 (Power−On Default = 0xFF)
Bit
<0>
<1>
Name
RS0
R/W
R/W
R/W
Description
Logic 1 enables the Repeated Start protocol for SMBus Slave Device 0
Logic 1 enables the Repeated Start protocol for SMBus Slave Device 1
RS1
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Table 119. Register 0xB0 − SMBus Master Configuration 1 (Power−On Default = 0xFF)
Bit
Name
RS2
RS3
RS4
RS5
RS6
RS7
R/W
R/W
R/W
R/W
R/W
R/W
R/W
Description
<2>
<3>
<4>
<5>
<6>
<7>
Logic 1 enables the Repeated Start protocol for SMBus Slave Device 2
Logic 1 enables the Repeated Start protocol for SMBus Slave Device 3
Logic 1 enables the Repeated Start protocol for SMBus Slave Device 4
Logic 1 enables the Repeated Start protocol for SMBus Slave Device 5
Logic 1 enables the Repeated Start protocol for SMBus Slave Device 6
Logic 1 enables the Repeated Start protocol for SMBus Slave Device 7
Table 120. REGISTER 0xB1 − SMBus Master Configuration 2 (Power−On Default = 0x00)
Bit
Name
PEC0
PEC1
PEC2
PEC3
PEC4
PEC5
PEC6
PEC7
R/W
R/W
R/W
R/W
R/W
R/W
R/W
R/W
R/W
Description
Logic 1 enables PEC byte support for SMBus Slave Device 0
Logic 1 enables PEC byte support for SMBus Slave Device 1
Logic 1 enables PEC byte support for SMBus Slave Device 2
Logic 1 enables PEC byte support for SMBus Slave Device 3
Logic 1 enables PEC byte support for SMBus Slave Device 4
Logic 1 enables PEC byte support for SMBus Slave Device 5
Logic 1 enables PEC byte support for SMBus Slave Device 6
Logic 1 enables PEC byte support for SMBus Slave Device 7
<0>
<1>
<2>
<3>
<4>
<5>
<6>
<7>
Table 121. REGISTER 0xB2 − SMBus Master Configuration 3 (Power−On Default = 0x03)
Bit
Name
R/W
Description
<1:0>
TMFT0
R/W
SMBus Device 0 temperature format:
00 = 8−bit 2’s Complement
01 = JEDEC SPD format
10 = 8−bit straight binary
11 = Block reads enabled
<3:2>
<5:4>
<7:6>
TMFT1
TMFT2
TMFT3
R/W
R/W
R/W
SMBus Device 1 temperature format:
00 = 8−bit 2’s Complement
01 = JEDEC SPD format
10 = 8−bit straight binary
11 = Block reads enabled
SMBus Device 2 temperature format:
00 = 8−bit 2’s Complement
01 = JEDEC SPD format
10 = 8−bit straight binary
11 = Block reads enabled
SMBus Device 3 temperature format:
00 = 8−bit 2’s Complement
01 = JEDEC SPD format
10 = 8−bit straight binary
11 = Block reads enabled
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Table 122. REGISTER 0xB3 − SMBus Master Configuration 4 (Power−On Default = 0x00)
Bit
Name
R/W
Description
<1:0>
TMFT4
R/W
SMBus Device 4 temperature format:
00 = 8−bit 2’s Complement
01 = JEDEC SPD format
10 = 8−bit straight binary
11 = Reserved
<3:2>
<5:4>
<7:6>
TMFT5
TMFT6
TMFT7
R/W
R/W
R/W
SMBus Device 5 temperature format:
00 = 8−bit 2’s Complement
01 = JEDEC SPD format
10 = 8−bit straight binary
11 = Literal Format
SMBus Device 6 temperature format:
00 = 8−bit 2’s Complement
01 = JEDEC SPD format
10 = 8−bit straight binary
11 = Literal Format
SMBus Device 7 temperature format:
00 = 8−bit 2’s Complement
01 = JEDEC SPD format
10 = 8−bit straight binary
11 = Literal Format
Table 123. REGISTER 0xB5 − SMBus Master Configuration 5 (Power−On Default = 0x08)
Bit
Name
R/W
Description
<0>
SMBEN
R/W
0 = SMBus Master disabled
1 = SMBus Master enabled
<4:1>
<5>
SHYS
R1DIMM
R2DIMM
PCHDIMM
R/W
R/W
R/W
R/W
SMBus Device temperature hysteresis
1 = Over−write DIMM0/DIMM1 value registers with Remote1 value
1 = Over−write DIMM2/DIMM3 value registers with Remote2 value
<6>
<7>
1 = Read DIMM temperatures from PCH. This setting overrides bits 5 and 6 of this register.
0 = Read DIMM temperatures from SMBus digital sensors
Table 124. REGISTER 0xB6 − SMBus Master Status 1 (Power−On Default = 0x00)
Bit
Name
NACK0
NACK1
NACK2
NACK3
NACK4
NACK5
NACK6
NACK7
R/W
Read
Read
Read
Read
Read
Read
Read
Read
Description
Logic 1 indicates a No Acknowledge from SMBus Device 0
Logic 1 indicates a No Acknowledge from SMBus Device 1
Logic 1 indicates a No Acknowledge from SMBus Device 2
Logic 1 indicates a No Acknowledge from SMBus Device 3
Logic 1 indicates a No Acknowledge from SMBus Device 4
Logic 1 indicates a No Acknowledge from SMBus Device 5
Logic 1 indicates a No Acknowledge from SMBus Device 6
Logic 1 indicates a No Acknowledge from SMBus Device 7
<0>
<1>
<2>
<3>
<4>
<5>
<6>
<7>
Table 125. REGISTER 0xB7 − SMBus Master Status 2 (Power−On Default = 0x00)
Bit
Name
PEC0
PEC1
PEC2
PEC3
R/W
Read
Read
Read
Read
Description
Logic 1 indicates an SMBus Device 0 PEC error
<0>
<1>
<2>
<3>
Logic 1 indicates an SMBus Device 1 PEC error
Logic 1 indicates an SMBus Device 2 PEC error
Logic 1 indicates an SMBus Device 3 PEC error
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NCT7491
Table 125. REGISTER 0xB7 − SMBus Master Status 2 (Power−On Default = 0x00)
Bit
Name
PEC4
PEC5
PEC6
PEC7
R/W
Read
Read
Read
Read
Description
Logic 1 indicates an SMBus Device 4 PEC error
<4>
<5>
<6>
<7>
Logic 1 indicates an SMBus Device 5 PEC error
Logic 1 indicates an SMBus Device 6 PEC error
Logic 1 indicates an SMBus Device 7 PEC error
Table 126. REGISTER 0xB8 − SMBus Master Status 3 (Power−On Default = 0x00)
Bit
Name
TO0
TO1
TO2
TO3
TO4
TO5
TO6
TO7
R/W
Read
Read
Read
Read
Read
Read
Read
Read
Description
Logic 1 indicates an SMBus Device 0 timeout error
<0>
<1>
<2>
<3>
<4>
<5>
<6>
<7>
Logic 1 indicates an SMBus Device 1 timeout error
Logic 1 indicates an SMBus Device 2 timeout error
Logic 1 indicates an SMBus Device 3 timeout error
Logic 1 indicates an SMBus Device 4 timeout error
Logic 1 indicates an SMBus Device 5 timeout error
Logic 1 indicates an SMBus Device 6 timeout error
Logic 1 indicates an SMBus Device 7 timeout error
Table 127. REGISTER 0xB9 − SMBus Master Status 4 (Power−On Default = 0x00)
Bit
Name
HILO0
HILO1
HILO2
HILO3
HILO4
HILO5
HILO6
HILO7
R/W
Read
Read
Read
Read
Read
Read
Read
Read
Description
<0>
<1>
<2>
<3>
<4>
<5>
<6>
<7>
Logic 1 indicates that the SMBus Device 0 reading is out of limits
Logic 1 indicates that the SMBus Device 1 reading is out of limits
Logic 1 indicates that the SMBus Device 2 reading is out of limits
Logic 1 indicates that the SMBus Device 3 reading is out of limits
Logic 1 indicates that the SMBus Device 4 reading is out of limits
Logic 1 indicates that the SMBus Device 5 reading is out of limits
Logic 1 indicates that the SMBus Device 6 reading is out of limits
Logic 1 indicates that the SMBus Device 7 reading is out of limits
Table 128. REGISTER 0Xba − SMBus Master Status 5 (Power−On Default = 0x00)
Bit
Name
TIV0
R/W
Read
Read
Read
Read
Read
Read
Read
Read
Description
Logic 1 indicates that the PCH returned a reserved temperature code
Logic 1 indicates that the PCH returned a reserved temperature code
Logic 1 indicates that the PCH returned a reserved temperature code
Logic 1 indicates that the PCH returned a reserved temperature code
Logic 1 indicates that the PCH returned a reserved temperature code
Reserved
<0>
<1>
<2>
<3>
<4>
<5>
<6>
<7>
TIV1
TIV2
TIV3
TIV4
Reserved
Reserved
Reserved
Reserved
Reserved
Table 129. REGISTER 0Xbb − SMBus Master Status 6 (Power−On Default = 0x00)
Bit
<0>
<1>
<2>
Name
TH0
R/W
Read
Read
Read
Description
Logic 1 indicates that the SMBus Device 0 reading is above the programmed THERM Limit
Logic 1 indicates that the SMBus Device 1 reading is above the programmed THERM Limit
Logic 1 indicates that the SMBus Device 2 reading is above the programmed THERM Limit
TH1
TH2
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Table 129. REGISTER 0Xbb − SMBus Master Status 6 (Power−On Default = 0x00)
Bit
Name
TH3
TH4
TH5
TH6
TH7
R/W
Read
Read
Read
Read
Read
Description
<3>
<4>
<5>
<6>
<7>
Logic 1 indicates that the SMBus Device 3 reading is above the programmed THERM Limit
Logic 1 indicates that the SMBus Device 4 reading is above the programmed THERM Limit
Logic 1 indicates that the SMBus Device 5 reading is above the programmed THERM Limit
Logic 1 indicates that the SMBus Device 6 reading is above the programmed THERM Limit
Logic 1 indicates that the SMBus Device 7 reading is above the programmed THERM Limit
Table 130. REGISTER 0xBC − SMBus Master Mask 1 (Power−On Default = 0x00)
Bit
Name
NACK0
NACK1
NACK2
NACK3
NACK4
NACK5
NACK6
NACK7
R/W
R/W
R/W
R/W
R/W
R/W
R/W
R/W
R/W
Description
<0>
<1>
<2>
<3>
<4>
<5>
<6>
<7>
Logic 1 masks a No Acknowledge assertion for SMBus Device 0
Logic 1 masks a No Acknowledge assertion for SMBus Device 1
Logic 1 masks a No Acknowledge assertion for SMBus Device 2
Logic 1 masks a No Acknowledge assertion for SMBus Device 3
Logic 1 masks a No Acknowledge assertion for SMBus Device 4
Logic 1 masks a No Acknowledge assertion for SMBus Device 5
Logic 1 masks a No Acknowledge assertion for SMBus Device 6
Logic 1 masks a No Acknowledge assertion for SMBus Device 7
Table 131. REGISTER 0xBD − SMBus Master Mask 2 (Power−On Default = 0x00)
Bit
Name
PEC0
PEC1
PEC2
PEC3
PEC4
PEC5
PEC6
PEC7
R/W
R/W
R/W
R/W
R/W
R/W
R/W
R/W
R/W
Description
Logic 1 masks a PEC error assertion for SMBus Device 0
Logic 1 masks a PEC error assertion for SMBus Device 1
Logic 1 masks a PEC error assertion for SMBus Device 2
Logic 1 masks a PEC error assertion for SMBus Device 3
Logic 1 masks a PEC error assertion for SMBus Device 4
Logic 1 masks a PEC error assertion for SMBus Device 5
Logic 1 masks a PEC error assertion for SMBus Device 6
Logic 1 masks a PEC error assertion for SMBus Device 7
<0>
<1>
<2>
<3>
<4>
<5>
<6>
<7>
Table 132. REGISTER 0Xbe − SMBus Master Mask 3 (Power−On Default = 0x00)
Bit
Name
TO0
TO1
TO2
TO3
TO4
TO5
TO6
TO7
R/W
R/W
R/W
R/W
R/W
R/W
R/W
R/W
R/W
Description
Logic 1 masks a timeout error assertion for SMBus Device 0
Logic 1 masks a timeout error assertion for SMBus Device 1
Logic 1 masks a timeout error assertion for SMBus Device 2
Logic 1 masks a timeout error assertion for SMBus Device 3
Logic 1 masks a timeout error assertion for SMBus Device 4
Logic 1 masks a timeout error assertion for SMBus Device 5
Logic 1 masks a timeout error assertion for SMBus Device 6
Logic 1 masks a timeout error assertion for SMBus Device 7
<0>
<1>
<2>
<3>
<4>
<5>
<6>
<7>
Table 133. REGISTER 0Xbf − SMBus Master Mask 4 (Power−On Default = 0x00)
Bit
<0>
<1>
Name
HILO0
HILO1
R/W
R/W
R/W
Description
Logic 1 masks limit assertions for SMBus Device 0
Logic 1 masks limit assertions for SMBus Device 1
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Table 133. REGISTER 0Xbf − SMBus Master Mask 4 (Power−On Default = 0x00)
Bit
Name
HILO2
HILO3
HILO4
HILO5
HILO6
HILO7
R/W
R/W
R/W
R/W
R/W
R/W
R/W
Description
Logic 1 masks limit assertions for SMBus Device 2
<2>
<3>
<4>
<5>
<6>
<7>
Logic 1 masks limit assertions for SMBus Device 3
Logic 1 masks limit assertions for SMBus Device 4
Logic 1 masks limit assertions for SMBus Device 5
Logic 1 masks limit assertions for SMBus Device 6
Logic 1 masks limit assertions for SMBus Device 7
Table 134. REGISTER 0xC0 − SMBus Master Mask 5 (Power−On Default = 0x00)
Bit
Name
TIV0
TIV1
TIV2
TIV3
TIV4
TIV5
TIV6
TIV7
R/W
R/W
R/W
R/W
R/W
R/W
R/W
R/W
R/W
Description
Logic 1 masks data invalid assertion for SMBus Device 0
Logic 1 masks data invalid assertion for SMBus Device 1
Logic 1 masks data invalid assertion for SMBus Device 2
Logic 1 masks data invalid assertion for SMBus Device 3
Logic 1 masks data invalid assertion for SMBus Device 4
Logic 1 masks data invalid assertion for SMBus Device 5
Logic 1 masks data invalid assertion for SMBus Device 6
Logic 1 masks data invalid assertion for SMBus Device 7
<0>
<1>
<2>
<3>
<4>
<5>
<6>
<7>
Table 135. SMBus MASTER LIMIT REGISTERS
Register Address
R/W
Description
Power−On Default
0xC1
R/W
SMBus Device High Limit.
0x7F
Programmed as an unsigned 8−bit value
0xC2
R/W
SMBus Device Low Limit.
0x81
Programmed as an 8−bit 2’s complement value.
Table 136. SMBus MASTER THERM LIMIT REGISTERS
Register Address
R/W
Description
Power−On Default
0xC3
R/W
SMBus Device THERM Limit.
Programmed as an unsigned 8−bit value
0x64
Table 137. SMBus DEVICE TMIN REGISTER
Register Address
R/W
Description
Power−On Default
0xC6
R/W
SMBus Device Tmin value. This sets the the temperature at which fans
controlled by any SMBus slave device will turn on.
0x5A
Programmed as an unsigned 8−bit value in the range 0°C to 175°C.
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NCT7491
Table 138. REGISTER 0xC7 − SMBus Master Trange/Interval (Power−On Default = 0x0C)
Bit
Name
R/W
Description
<3:0>
RNG
R/W
These bits determine the PWM duty cycle vs. the temperature range for automatic fan control.
0000 = 2°C
0001 = 2.5°C
0010 = 3.33°C
0011 = 4°C
0100 = 5°C
0101 = 6.67°C
0110 = 8°C
0111 = 10°C
1000 = 13.33°C
1001 = 16°C
1010 = 20°C
1011 = 26.67°C
1100 = 32°C (default)
1101 = 40°C
1110 = 53.33°C
1111 = 80°C
<5:4>
<7:6>
Reserved
SMBINT
R/W
Sets the SMBus Master loop time
00 = 250 ms
01 = 500 ms
10 = 750 ms
11 = 1 sec
Table 139. PUSH TEMPERATURE REGISTERS
Register Address
R/W
Description
Power−On Default
0xC8
R/W
Push0. This register is programmable by an external master to allow tem-
peratures gathered externally to be used by the NCT7491 fan control loop
0x00
0xC9
0xCA
0xCB
R/W
R/W
Push1. This register is programmable by an external master to allow tem-
peratures gathered externally to be used by the NCT7491 fan control loop
0x00
0x00
0x00
Push2. This register is programmable by an external master to allow tem-
peratures gathered externally to be used by the NCT7491 fan control loop
Push3. This register is programmable by an external master to allow tem-
peratures gathered externally to be used by the NCT7491 fan control loop
Table 140. PUSH TMIN REGISTER
Register Address
R/W
Description
Power−On Default
0xCC
R/W
Push Device Tmin value. This sets the the temperature at which fans con-
trolled by any SMBus slave device will turn on. This value applies to all 4
Push temperature registers.
0x5A
This value should be programmed in the range 0°C to 127°C
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Table 141. REGISTER 0xCD − Push Trange (Power−On Default = 0x0C)
Bit
Name
R/W
Description
<3:0>
RNG
R/W
These bits determine the PWM duty cycle vs. the temperature range for automatic fan control.
0000 = 2°C
0001 = 2.5°C
0010 = 3.33°C
0011 = 4°C
0100 = 5°C
0101 = 6.67°C
0110 = 8°C
0111 = 10°C
1000 = 13.33°C
1001 = 16°C
1010 = 20°C
1011 = 26.67°C
1100 = 32°C (default)
1101 = 40°C
1110 = 53.33°C
1111 = 80°C
<7:4>
Reserved
Table 142. PUSH TEMPERATURE LIMIT REGISTERS
Register Address
R/W
R/W
R/W
R/W
Description
Push High Limit
Push Low Limit
Push THERM Limit
Power−On Default
0xCE
0xCF
0xD0
0x7F
0x81
0x64
Table 143. GENERIC PECI INTERFACE BLOCK
Register Address
R/W
Description
Default
0xD1
R/W
Generic PECI CPU Address. This sets the target processor address for the
PECI command
0x00
0xD2
R/W
Write Length. This sets the number of byte transferred to the target device
when the command is executed
0x00
0xD3
0xD4
0xD5
0xD6
0xD7
0xD8
0xD9
0xDA
0xDB
0xDC
0xDD
0xDE
0xDF
0xE0
0xE1
0xE2
0xE3
0xE4
0xE5
R/W
R/W
R/W
R/W
R/W
R/W
R/W
R/W
R/W
R/W
R/W
R/W
R/W
R/W
R/W
R/W
R/W
R/W
R/W
Read Length. This specifies the number of bytes to be returned by the target.
0x00
0x00
0x00
0x00
0x00
0x00
0x00
0x00
0x00
0x00
0x00
0x00
0x00
0x00
0x00
0x00
0x00
0x00
0x00
st
WRDAT0; The 1 byte to be transferred (Command Code)
nd
WRDAT1; 2 byte to be transferred
rd
WRDAT2; 3 byte to be transferred
th
WRDAT3; 4 byte to be transferred
th
WRDAT4; 5 byte to be transferred
WRDAT5; 6th byte to be transferred
WRDAT6; 7th byte to be transferred
WRDAT7; 8th byte to be transferred
WRDAT8; 9th byte to be transferred
WRDAT9; 10th byte to be transferred
WRDAT10; 11th byte to be transferred
WRDAT11; 12th byte to be transferred
WRDAT12; 13th byte to be transferred
st
RDDAT0; The 1 byte returned
nd
RDDAT1; The 2 byte returned
rd
RDDAT2; The 3 byte returned
th
RDDAT3; The 4 byte returned
th
RDDAT4; The 5 byte returned
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76
NCT7491
Table 143. GENERIC PECI INTERFACE BLOCK
Register Address
R/W
R/W
R/W
R/W
R/W
Description
Default
0x00
th
0xE6
0xE7
0xE8
0xE9
RDDAT5; The 6 byte returned
th
RDDAT6; The 7 byte returned
0x00
th
RDDAT6; The 8 byte returned
0x00
th
RDDAT6; The 9 byte returned
0x00
Table 144. REGISTER 0xEA − PECI Configuration 5 (Power−On Default = 0x00)
Bit
<0>
<1>
Name
Reserved
AW
R/W
Description
R/W
Logic 1 indicates that the command is an Assured Write command. The AW byte is automat-
ically calculated and appended by the NCT7491. Even though the user does not program the
AW value the Write Length register for an Assured Write command should include the AW
byte (for example, if 5 bytes are to be written the Write length register should be set to 6 as
the AW byte will be added to the end of the write sequence)
<2>
PEX
R/W
Logic 1 will cause the programmed PECI command sequence to be executed. This bit will
automatically clear when the command has completed.
<7:3>
Reserved
Table 145. REGISTER 0xEB − Push Hysteresis (Power−On Default = 0x04)
Bit
Name
R/W
Description
<3:0>
<7:4>
Push Hyst
Reserved
R/W
Sets the hysteresis value associated with the Push temperature registers
Table 146. REGISTER 0xFF − Page Select
Bit
<0>
Name
RGMP
R/W
R/W
R
Description
1 = Selects register map page 1
<7:1>
Reserved
Table 147. FAN1 LOOK UP TABLE
Register Address
0x100
R/W
R/W
R/W
R/W
R/W
R/W
R/W
R/W
R/W
R/W
R/W
R/W
R/W
R/W
R/W
R/W
R/W
Description
Default
0x00
0xFF
0x00
0xFF
0x00
0xFF
0x00
0xFF
0x00
0xFF
0x00
0xFF
0x00
0xFF
0x00
0xFF
Sets the temperature for the 1st LUT point for Fan1
Sets the PWM output for the 1st LUT point for Fan1
Sets the temperature for the 2nd LUT point for Fan1
Sets the PWM output for the 2nd LUT point for Fan1
Sets the temperature for the 3rd LUT point for Fan1
Sets the PWM output for the 3rd LUT point for Fan1
Sets the temperature for the 4th LUT point for Fan1
Sets the PWM output for the 4th LUT point for Fan1
Sets the temperature for the 5th LUT point for Fan1
Sets the PWM output for the 5th LUT point for Fan1
Sets the temperature for the 6th LUT point for Fan1
Sets the PWM output for the 6th LUT point for Fan1
Sets the temperature for the 7th LUT point for Fan1
Sets the PWM output for the 7th LUT point for Fan1
Sets the temperature for the 8th LUT point for Fan1
Sets the PWM output for the 8th LUT point for Fan1
0x101
0x102
0x103
0x104
0x105
0x106
0x107
0x108
0x109
0x10A
0x10B
0x10C
0x10D
0x10E
0x10F
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NCT7491
Table 148. FAN2 LOOK UP TABLE
Register Address
0x110
R/W
R/W
R/W
R/W
R/W
R/W
R/W
R/W
R/W
R/W
R/W
R/W
R/W
R/W
R/W
R/W
R/W
Description
Default
0xFF
0xFF
0xFF
0xFF
0xFF
0xFF
0xFF
0xFF
0xFF
0xFF
0xFF
0xFF
0xFF
0xFF
0xFF
0xFF
Sets the temperature for the 1st LUT point for Fan2
Sets the PWM output for the 1st LUT point for Fan2
Sets the temperature for the 2nd LUT point for Fan2
Sets the PWM output for the 2nd LUT point for Fan2
Sets the temperature for the 3rd LUT point for Fan2
Sets the PWM output for the 3rd LUT point for Fan2
Sets the temperature for the 4th LUT point for Fan2
Sets the PWM output for the 4th LUT point for Fan2
Sets the temperature for the 5th LUT point for Fan2
Sets the PWM output for the 5th LUT point for Fan2
Sets the temperature for the 6th LUT point for Fan2
Sets the PWM output for the 6th LUT point for Fan2
Sets the temperature for the 7th LUT point for Fan2
Sets the PWM output for the 7th LUT point for Fan2
Sets the temperature for the 8th LUT point for Fan2
Sets the PWM output for the 8th LUT point for Fan2
0x111
0x112
0x113
0x114
0x115
0x116
0x117
0x118
0x119
0x11A
0x11B
0x11C
0x11D
0x11E
0x11F
Table 149. FAN3 LOOK UP TABLE
Register Address
0x120
R/W
R/W
R/W
R/W
R/W
R/W
R/W
R/W
R/W
R/W
R/W
R/W
R/W
R/W
R/W
R/W
R/W
Description
Default
0xFF
0xFF
0xFF
0xFF
0xFF
0xFF
0xFF
0xFF
0xFF
0xFF
0xFF
0xFF
0xFF
0xFF
0xFF
0xFF
Sets the temperature for the 1st LUT point for Fan3
Sets the PWM output for the 1st LUT point for Fan3
Sets the temperature for the 2nd LUT point for Fan3
Sets the PWM output for the 2nd LUT point for Fan3
Sets the temperature for the 3rd LUT point for Fan3
Sets the PWM output for the 3rd LUT point for Fan3
Sets the temperature for the 4th LUT point for Fan3
Sets the PWM output for the 4th LUT point for Fan3
Sets the temperature for the 5th LUT point for Fan3
Sets the PWM output for the 5th LUT point for Fan3
Sets the temperature for the 6th LUT point for Fan3
Sets the PWM output for the 6th LUT point for Fan3
Sets the temperature for the 7th LUT point for Fan3
Sets the PWM output for the 7th LUT point for Fan3
Sets the temperature for the 8th LUT point for Fan3
Sets the PWM output for the 8th LUT point for Fan3
0x121
0x122
0x123
0x124
0x125
0x126
0x127
0x128
0x129
0x12A
0x12B
0x12C
0x12D
0x12E
0x12F
Table 150. REGISTER 0x1FF − Page Select Clear
Bit
<0>
Name
RGMP
R/W
R/W
R
Description
0 = Selects register map page 0
<7:1>
Reserved
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78
NCT7491
ORDERING INFORMATION
Model
†
Termperature Range
Package Type
Shipping
NCT7491RQR2G
−40°C to +125°C
QSOP24
(Pb−Free)
4000 / Tape & Reel
2500 / Tape & Reel
NCT7491MNTXG
–40°C to +125°C
QFN24
(Pb−Free)
†For information on tape and reel specifications, including part orientation and tape sizes, please refer to our Tape and Reel Packaging
Specifications Brochure, BRD8011/D.
PACKAGE DIMENSIONS
QSOP24 NB
CASE 492B
ISSUE A
2X
NOTES:
1. DIMENSIONING AND TOLERANCING PER ASME
Y14.5M, 1994.
2. CONTROLLING DIMENSION: MILLIMETERS.
3. DIMENSION b DOES NOT INCLUDE DAMBAR
PROTRUSION.
4. DIMENSION D DOES NOT INCLUDE MOLD FLASH,
PROTRUSIONS, OR GATE BURRS. MOLD FLASH,
PROTRUSIONS, OR GATE BURRS SHALL NOT
EXCEED 0.15 PER SIDE. DIMENSION E1 DOES NOT
INCLUDE INTERLEAD FLASH OR PROTRUSION.
INTERLEAD FLASH OR PROTRUSION SHALL NOT
EXCEED 0.15 PER SIDE. D AND E1 ARE
DETERMINED AT DATUM H.
0.20 C
D
D
D
GAUGE
PLANE
A
C
24
13
L2
E
E1
C
L
DETAIL A
2X
5. DATUMS A AND B ARE DETERMINED AT DATUM H.
2X 12 TIPS
0.20 C
D
MILLIMETERS
1
12
DIM
A
MIN
1.35
0.10
0.20
0.19
MAX
1.75
0.25
0.30
0.25
0.25 C
D
24X b
A1
b
e
M
0.25
C A-B D
B
h x 45
_
C
D
8.65 BSC
A
H
0.10
0.10
C
C
E
6.00 BSC
3.90 BSC
0.635 BSC
E1
e
h
0.22
0.40
0.50
L
1.27
A1
L2
M
0.25 BSC
SEATING
PLANE
24X
M
C
0
8
DETAIL A
_
_
SOLDERING FOOTPRINT
24X
0.42
24X
1.12
24
13
6.40
1
12
0.635
PITCH
DIMENSIONS: MILLIMETERS
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79
NCT7491
PACKAGE DIMENSIONS
QFN24, 4x4, 0.5P
CASE 485L
ISSUE B
NOTES:
1. DIMENSIONING AND TOLERANCING PER ASME
Y14.5M, 1994.
2. CONTROLLING DIMENSION: MILLIMETERS.
3. DIMENSION b APPLIES TO PLATED TERMINAL
AND IS MEASURED BETWEEN 0.25 AND 0.30 MM
FROM THE TERMINAL TIP.
L
L
D
A
B
PIN 1
REFEENCE
L1
DETAIL A
ALTERNATE
CONSTRUCTIONS
4. COPLANARITY APPLIES TO THE EXPOSED PAD
AS WELL AS THE TERMINALS.
E
2X
MILLIMETERS
0.15
C
DIM MIN
MAX
1.00
0.05
A3
A
A1
A3
b
0.80
0.00
EXPOSED Cu
MOLD CMPD
2X
0.15
C
TOP VIEW
0.20 REF
0.20
0.30
2.90
D
4.00 BSC
DETAIL B
D2
E
2.70
2.70
A1
0.10
0.08
C
C
4.00 BSC
DETAIL B
ALTERNATE TERMINAL
CONSTRUCTIONS
E2
e
2.90
A
0.50 BSC
L
0.30
0.05
0.50
0.15
A3
L1
SEATING
PLANE
C
NOTE 4
A1
SIDE VIEW
RECOMMENDED
SOLDERING FOOTPRINT
D2
DETAIL A
24X L
4.30
7
24X
0.55
2.90
13
E2
1
1
24
19
24X b
2.90
4.30
e
e/2
0.10 C A B
NOTE 3
0.05 C
BOTTOM VIEW
24X
0.32
0.50
PITCH
DIMENSIONS: MILLIMETERS
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