MAXSMBUS [MAXIM]
2-Wire Interface Board; 2线接口板
| 型号： | MAXSMBUS |
| 厂家： | 
MAXIM INTEGRATED PRODUCTS |
| 描述： | 2-Wire Interface Board |
| 文件： | 总8页 (文件大小：221K) |
| 中文： | 中文翻译 | 下载： | 下载PDF数据表文档文件 |
19-1629; Rev 1; 2/00
2-Wire Interface Board
________________General Description
____________________________Features
ꢀ SMBus-Compatible 2-Wire Interface
ꢀ SMBus Suspend Output
MAXSMBus is an interface between an IBM-compatible
PC and System Management Bus (SMBus™)-
compatible serial-interface devices such as tempera-
ture monitors, voltage regulators, or A/D converters
(ADCs). The MAXSMBus interface board is connected
between the PC parallel port and the device under test,
converting parallel data into 2-wire, open-drain serial
data. The board is provided for use with selected
Maxim products and is not intended to replace com-
mercially available SMBus hardware. MAXSMBus is
shipped with a companion EV kit board, including all
relevant software.
ꢀ Two SMBus Alert Inputs
ꢀ Overvoltage Fault Protection
ꢀ PC Parallel Port Interface
_______________Ordering Information
PART
BOARD TYPE
Note that the MAXSMBus board, combined with a PC,
is intended only for the functional evaluation of Maxim
SMBus-interfaced devices. The PC functions as the
only bus master, and does not yield to any other SMBus
master. The SMBus emulation system is not designed
to meet all of the SMBus specifications.
MAXSMBus
Companion Board for SMBus EV Kits
___MAXSMBus Functionality Check
Follow these steps to verify that the MAXSMBus inter-
face board is functioning properly. All necessary soft-
ware is supplied on a disk with the companion EV kit.
Instructions for operating the software are included in
the EV kit manual.
MAXSMBus Interface Board
____________________________Component List
1) Connect a +9VDC supply (+7V minimum, +30V
maximum) to the MAXSMBus interface board at the
terminals labeled POS9 and GND in the lower left
corner of the board.
DESIGNATION QTY
DESCRIPTION
0.1µF ceramic capacitors
3.3µF, 20V tantalum capacitors
2.2µF, 35V tantalum capacitor
1N4692 zener diode, 6.8V
1N4688 zener diode, 4.7V
1N4148 small-signal diode
DB25 right-angle plug
C1, C2, C3
3
5
1
1
1
1
1
0
1
C4–C7, C9
C8
D1
D2
D3
J1
2) Use a digital voltmeter to verify that the oval pad
labeled POS5 is +5V (+4.75V minimum, +5.25V
maximum). Also verify that the pads labeled
SBDAT1, SBCLK1, SBSUS1, ALERT1, and ALERT2
are above +4V.
3) If these DC voltages are correct, MAXSMBus pass-
es the functionality test.
J2
Not installed
P1
2x10 right-angle male header
_______________Detailed Description
R1, R2, R3,
R8–R11
The MAXSMBus interface board provides all of the
interface signals necessary to interface an IBM PC-
compatible computer with an SMBus-compliant device.
A DB25 right-angle plug connects to the computer
(Table 1). The companion board plugs into a 20-pin
dual-row right-angle header at the edge of the board
(Table 2). Alternatively, connection can be made by
soldering wires to the oval pads as appropriate. This
allows the companion board to be placed in an environ-
mental chamber for evaluation over temperature.
7
47k
5ꢀ resistors
5ꢀ resistors
R4–R7
U1
4
1
1
1
1
4.7k
74HCT05 hex open-collector inverter
74HCT04 hex inverter
U2
U3
74HCT08 quad AND gate
74HCT74 dual D flip-flop
U4
+5V, 100mA regulator
LM78L05ACM
U5
1
Refer to the documentation of the companion Maxim EV
kit for quick start and operating instructions.
U6
U7
1
1
1
MAX865EUA (8-pin µMAX)
MAX367CWN (18-pin SO)
PC board
NONE
SMBus is a trademark of Intel Corp.
________________________________________________________________ Maxim Integrated Products
1
For pricing, delivery, and ordering information, please contact Maxim/Dallas Direct! at
1-888-629-4642, or visit Maxim’s website at www.maxim-ic.com.
2-Wire Interface Board
Power Supply
The interface board is powered by a 78L05 linear regu-
lator. The companion board can draw about 20mA of
+5V power through the circuit protector. Companion
boards that require more power must provide their own
regulator. The unregulated input to the 78L05 is avail-
able on the right-angle header.
Bus Driving Circuitry
A 74HCT05 open-drain inverter (U1) is used to pull
down the SMBus interface signals. The 74HCT08 (U3),
74HCT74 (U4), and 74HCT04 (U2) buffer the signal to
the IBM PC and provide the capability to mask the
ALERT interrupts, detect an externally generated start
condition, and capture data sent by an external bus
master. Interface connections are listed in Table 1 and
Table 2.
Fault-Protection Circuitry
Overvoltage fault protection is provided by a MAX367
fault protector (U7). If any of the SMBus interface sig-
nals exceed the MAX367’s power-supply rails, the
MAX367 increases its resistance to prevent damage to
the user’s computer. A MAX865 dual charge pump
(U6) and two zener diodes (D1 and D2) provide +7V
and -3V supplies to the MAX367, thus allowing 0 and
+5V signals to pass with a nominal resistance of 100 .
Bus Monitoring Circuitry
Flip-flop U4A detects the start condition (falling edge of
SMBDATA when SMBCLK is high). Flip-flop U4B
detects the falling SMBCLK edge when enabled, and
U1F holds SMBCLK low until the software releases it.
To advance to the next data bit, the software uses U1A
to assert and then release SMBCLK. A logic high at the
input of U1A also resets flip-flop U4B. Because the IBM
PC parallel port has a limited number of inputs, the
start-detect circuit and the two alert inputs share a sin-
gle interrupt input. The source of the interrupt is distin-
guished using U3A, U3B, and U3C.
________________________________________________________Troubleshooting Guide
SYMPTOM
CAUSE
SOLUTION
Verify that the cable is a 25-pin parallel port I/O extension cable
with a plug on one end and a socket on the other end.
Verify that the cable is connected to a printer port, not a floppy
disk, SCSI, or serial communications port.
Board not connected to
parallel printer port
Can’t Find the Interface Board
Check power connections on the interface board.
Board is connected to cor- Check clock and data signal connections.
Clock or Data Stuck Low
rect port, but SMBus is not Try operating the interface board without the companion Maxim
functioning
evaluation kit—this should cause the address-not-acknowledged
symptom described below.
Verify that the companion board is connected to the MAXSMBus
interface board.
Verify that the companion board is powered.
If the companion offers a choice of addresses, confirm that the soft-
ware and hardware addresses match. Some devices only read the
address select pins at device power-up.
SMBus is OK, but no
response at expected
SMBus address
Address Not Acknowledged
Conflict with local printer
driver
Disable print manager in the Windows printer control panel. Disable
printer driver.
Erratic Operation
1) Use computer with commercially available BIOS.
2) Make a bootable floppy disk, remove unnecessary device dri-
vers from A:config.sys, and boot system from floppy.
Operating system conflict
2
_______________________________________________________________________________________
2-Wire Interface Board
Table 1. DB25 Connector Signals
PIN
NAME
FUNCTION
1
SPARE OUTPUT A
Spare output
-
2
When high, drives SMBCLK signal low
SMBCLK_OUT
-
3
When high, drives SMBDATA signal low
When high, drives SMBSUS signal low
SMBDATA_OUT
4
SMBUS_OUT
5
LOOPBACK
Loopback connection for port verification
When high, allows ALERT1 to trigger INT low
When high, allows ALERT2 to trigger INT low
When high, allows a start condition to trigger INT low
-
6
MASK_ALERT1
-
7
MASK_ALERT2
-
8
MASK_START
When high, enables slave / bus monitor circuitry. This circuit waits until SMBCLK
is pulled low, and then it holds SMBCLK until the software resets it.
9
CAPTURE_ENABLE
10
11
Active low interrupt input
INT
-
When high, indicates that SMBDATA is low
When high, indicates that SMBCLK is low
Loopback connection for port verification
Spare output
SMBDATA_IN
-
12
SMBCLK_IN
13
LOOPBACK
14
SPARE OUTPUT B
-
15
When low, indicates that interface board is holding SMBCLK low
Not used
HOLDING_CLOCK
16
UNUSED
UNUSED
GND
17
Not used
18–25
Signal ground return
_______________________________________________________________________________________
3
2-Wire Interface Board
Table 2. Right-Angle Header P1 Signals
PIN
NAME
DUT +5V
GND
FUNCTION
+5V at 1mA power supply to Maxim companion board
Signal ground return
1
2
3
DUT SDA
GND
SMBDATA interface signal
4
Signal ground return
5
GND
Signal ground return
6
GND
Signal ground return
7
DUT SCL
GND
SMBCLK interface signal
8
Signal ground return
9
DUT SMBSUS
GND
SMBSUS interface signal
10
11
12
13
14
15
16
17
18
19
20
Signal ground return
DUT SMBALERT
GND
Primary ALERT interface signal
Signal ground return
DUT ALERT2
GND
Secondary ALERT interface signal
Signal ground return
SPARE OUTPUT A
GND
Spare output from pin 1 of the DB25 connector
Signal ground return
SPARE OUTPUT B
GND
Spare output from pin 14 of the DB25 connector
Signal ground return
GND
Signal ground return
RAW POWER
Unregulated, unprotected power-supply input to MAXSMBus interface board
Note: Odd-numbered pins are on the outer row. Even-numbered pins are on the inner row. All right-angle header signals pass through
the MAX367 circuit protector, except 20.
4
_______________________________________________________________________________________
2-Wire Interface Board
Figure 1a. MAXSMBus Schematic
_______________________________________________________________________________________
5
2-Wire Interface Board
Figure 1b. MAXSMBus Schematic (continued)
6
_______________________________________________________________________________________
2-Wire Interface Board
1.0"
1.0"
Figure 2. MAXSMBus Component Placement Guide—
Component Side
Figure 3. MAXSMBus PC Board Layout—Component Side
_______________________________________________________________________________________
7
2-Wire Interface Board
1.0"
Figure 4. MAXSMBus PC Board Layout—Solder Side
Maxim cannot assume responsibility for use of any circuitry other than circuitry entirely embodied in a Maxim product. No circuit patent licenses are
implied. Maxim reserves the right to change the circuitry and specifications without notice at any time.
8 _____________________Maxim Integrated Products, 120 San Gabriel Drive, Sunnyvale, CA 94086 408-737-7600
© 2000 Maxim Integrated Products
Printed USA
is a registered trademark of Maxim Integrated Products.
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