CY14B256KA_11 [CYPRESS]
256-Kbit (32 K Ã 8) nvSRAM with Real Time Clock; 256千位（ 32 K A ?? 8 ）的nvSRAM具有实时时钟
| 型号： | CY14B256KA_11 |
| 厂家： | 
CYPRESS |
| 描述： | 256-Kbit (32 K Ã 8) nvSRAM with Real Time Clock |
| 文件： | 总27页 (文件大小：913K) |
| 中文： | 中文翻译 | 下载： | 下载PDF数据表文档文件 |
CY14B256KA
256-Kbit (32 K × 8) nvSRAM with
Real Time Clock
256 Kbit (32K
x 8) nvSRAM with Real Time Clock
■ Industry standard configurations
❐ Single 3 V +20%, -10% operation
❐ Industrial temperature
❐ 48-pin shrink small-outline package (SSOP)
❐ Pb-free and Restriction of hazardous substances (RoHS)
compliant
Features
■ 256-Kbit nonvolatile static random access memory (nvSRAM)
❐ 25 ns and 45 ns access times
❐ Internally organized as 32 K × 8 (CY14B256KA)
❐ HandsoffautomaticSTOREonpower-downwithonlyasmall
capacitor
Functional Description
❐ STORE to QuantumTrap nonvolatile elements is initiated by
software, hardware, or AutoStore on power-down
The Cypress CY14B256KA combines a 256-Kbit nonvolatile
static RAM with a full featured real time clock in a monolithic
integrated circuit. The embedded nonvolatile elements incor-
porate QuantumTrap technology producing the world’s most
reliable nonvolatile memory. The SRAM is read and written an
infinite number of times, while independent nonvolatile data
resides in the nonvolatile elements.
❐ RECALL to SRAM initiated on power-up or by software
■ High reliability
❐ Infinite Read, Write, and RECALL cycles
❐ 1 million STORE cycles to QuantumTrap
❐ 20 year data retention
■ Real time clock (RTC)
The real time clock function provides an accurate clock with leap
year tracking and a programmable, high accuracy oscillator. The
alarm function is programmable for periodic minutes, hours,
days, or months alarms. There is also a programmable watchdog
timer for process control.
❐ Full-featured real time clock
❐ Watchdog timer
❐ Clock alarm with programmable interrupts
❐ Capacitor or battery backup for RTC
❐ Backup current of 0.35 uA (Typ)
Logic Block Diagram
V
CC
V
CAP
QuantumTrap
512 X 512
V
RTCbat
POWER
A5
STORE
CONTROL
V
RTCcap
A6
A7
A8
RECALL
STORE/
RECALL
CONTROL
STATIC RAM
ARRAY
512 X 512
HSB
A9
A11
A12
A13
A14
SOFTWARE
DETECT
A14
-
A0
DQ0
COLUMN IO
DQ1
DQ2
DQ3
COLUMN DEC
xout
xin
RTC
MUX
INT
DQ4
DQ5
DQ6
DQ7
A0
A4
A10
A1
A3
A2
A14
-
A0
OE
CE
WE
Cypress Semiconductor Corporation
Document #: 001-55720 Rev. *C
•
198 Champion Court
•
San Jose, CA 95134-1709
•
408-943-2600
Revised January 17, 2011
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CY14B256KA
Contents
Pinouts .............................................................................. 3
Pin Definitions .................................................................. 3
Device Operation.............................................................. 4
SRAM Read ....................................................................... 4
SRAM Write....................................................................... 4
AutoStore Operation ........................................................ 4
Hardware STORE (HSB) Operation................................. 4
Hardware RECALL (Power-Up) ....................................... 5
Software STORE............................................................... 5
Software RECALL............................................................. 5
Preventing AutoStore....................................................... 6
Data Protection................................................................. 7
Noise Considerations....................................................... 7
Real Time Clock Operation.............................................. 7
nvTIME Operation ....................................................... 7
Clock Operations......................................................... 7
Reading the Clock....................................................... 7
Setting the Clock ......................................................... 7
Backup Power ............................................................. 7
Stopping and Starting the Oscillator............................ 8
Calibrating the Clock ................................................... 8
Alarm........................................................................... 8
Watchdog Timer.......................................................... 8
Power Monitor ............................................................. 9
Interrupts ..................................................................... 9
Flags Register ........................................................... 10
Best Practices................................................................. 15
Maximum Ratings........................................................... 16
Operating Range............................................................. 16
DC Electrical Characteristics ........................................ 16
Data Retention and Endurance ..................................... 17
Capacitance .................................................................... 17
Thermal Resistance........................................................ 17
AC Test Conditions ........................................................ 17
RTC Characteristics ....................................................... 17
AC Switching Characteristics ....................................... 18
SRAM Read Cycle .................................................... 18
SRAM Write Cycle..................................................... 18
AutoStore/Power-Up RECALL....................................... 20
Software Controlled STORE/RECALL Cycle................ 21
Hardware STORE Cycle ................................................. 22
Truth Table For SRAM Operations................................ 23
Ordering Information...................................................... 24
Ordering Code Definition........................................... 24
Package Diagram............................................................ 25
Acronyms........................................................................ 26
Document Conventions ................................................. 26
Units of Measure ....................................................... 26
Document History Page................................................. 27
Sales, Solutions, and Legal Information ...................... 27
Worldwide Sales and Design Support....................... 27
Products.................................................................... 27
PSoC Solutions......................................................... 27
Document #: 001-55720 Rev. *C
Page 2 of 27
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CY14B256KA
Pinouts
Figure 1. Pin Diagram - 48-Pin SSOP
VCAP
[1]
48
47
V
CC
1
2
3
[1]
NC
NC
A
14
A12
A
7
46
45
44
43
42
HSB
WE
A13
A8
4
5
6
7
8
9
10
11
12
13
14
A
6
A
5
INT
A
4
A
9
41
40
NC
A
48 - SSOP
(x8)
11
NC
NC
NC
VSS
39
NC
NC
NC
V
SS
NC
38
37
36
Top View
(not to scale)
NC
VRTCbat
35
15
16
17
18
19
20
21
22
23
24
VRTCcap
34
33
32
31
DQ0
A
DQ6
OE
A10
3
A
2
A
1
30
29
28
27
26
25
CE
DQ7
A
0
DQ1
DQ2
Xout
Xin
DQ5
DQ4
DQ3
V
CC
Pin Definitions
Pin Name
I/O Type
Input
Description
Address inputs. Used to select One of the 32,768 bytes of the nvSRAM.
A0 – A14
DQ0 – DQ7 Input/Output Bidirectional data I/O Lines. Used as input or output lines depending on operation.
NC
No connect No connect. This pin is not connected to the die.
Input
Write Enable input, Active LOW. When the chip is enabled and WE is LOW, data on the I/O pins is written
to the specific address location.
WE
Input
Input
Chip Enable input, Active LOW. When LOW, selects the chip. When HIGH, deselects the chip.
CE
OE
Output Enable, Active LOW. The active LOW OE input enables the data output buffers during read
cycles. Deasserting OE HIGH causes the I/O pins to tristate.
Xout
Xin
Output
Input
Crystal connection. Drives crystal on start up.
Crystal connection. For 32.768 kHz crystal.
VRTCcap
VRTCbat
Power supply Capacitor supplied backup RTC supply voltage. Left unconnected if VRTCbat is used.
Power supply Battery supplied backup RTC supply voltage. Left unconnected if VRTCcap is used.
Output
Interrupt output. Programmable to respond to the clock alarm, the watchdog timer, and the power
monitor. Also programmable to either active HIGH (push or pull) or LOW (open drain).
INT
VSS
VCC
Ground
Ground for the device. Must be connected to the ground of the system.
Power supply Power supply inputs to the Device. 3.0 V +20%, –10%
Input/Output Hardware STORE Busy (HSB). When LOW, this output indicates that a Hardware STORE is in progress.
When pulled LOW, external to the chip, it initiates a nonvolatile STORE operation. After each Hardware
and Software STORE operation HSB is driven HIGH for a short time (tHHHD) with standard output high
current and then a weak internal pull-up resistor keeps this pin HIGH (external pull-up resistor connection
optional).
HSB
VCAP
Power supply AutoStore capacitor. Supplies power to the nvSRAM during power loss to store data from SRAM to
nonvolatile elements.
Note
1. Address expansion for 1 Mbit. NC pin not connected to die.
Document #: 001-55720 Rev. *C
Page 3 of 27
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CY14B256KA
Figure 2. AutoStore Mode
Device Operation
VCC
The CY14B256KA nvSRAM is made up of two functional
components paired in the same physical cell. These are a SRAM
memory cell and a nonvolatile QuantumTrap cell. The SRAM
memory cell operates as a standard fast static RAM. Data in the
SRAM is transferred to the nonvolatile cell (the STORE
operation), or from the nonvolatile cell to the SRAM (the RECALL
operation). Using this unique architecture, all cells are stored and
recalled in parallel. During the STORE and RECALL operations
SRAM read and write operations are inhibited. The
CY14B256KA supports infinite reads and writes similar to a
typical SRAM. In addition, it provides infinite RECALL operations
from the nonvolatile cells and up to 1 million STORE operations.
Refer the Truth Table For SRAM Operations on page 23 for a
complete description of read and write modes.
0.1 uF
VCC
WE
VCAP
VCAP
VSS
SRAM Read
The CY14B256KA performs a read cycle whenever CE and OE
are LOW, and WE and HSB are HIGH. The address specified on
pins A0-14 determines which of the 32,768 data bytes are
accessed. When the read is initiated by an address transition,
the outputs are valid after a delay of tAA (read cycle #1). If the
read is initiated by CE or OE, the outputs are valid at tACE or at
Figure 2 shows the proper connection of the storage capacitor
(VCAP) for automatic STORE operation. Refer to DC Electrical
Characteristics on page 16 for the size of the VCAP. The voltage
on the VCAP pin is driven to VCC by a regulator on the chip. Place
a pull-up on WE to hold it inactive during power-up. This pull-up
is only effective if the WE signal is tristate during power-up. Many
MPUs tristate their controls on power-up. This must be verified
when using the pull-up. When the nvSRAM comes out of
power-on-RECALL, the MPU must be active or the WE held
inactive until the MPU comes out of reset.
t
DOE, whichever is later (read cycle #2). The data output
repeatedly responds to address changes within the tAA access
time without the need for transitions on any control input pins.
This remains valid until another address change or until CE or
OE is brought HIGH, or WE or HSB is brought LOW.
SRAM Write
To reduce unnecessary nonvolatile stores, AutoStore and
Hardware STORE operations are ignored unless at least one
write operation has taken place since the most recent STORE or
RECALL cycle. Software initiated STORE cycles are performed
regardless of whether a write operation has taken place.
A write cycle is performed when CE and WE are LOW and HSB
is HIGH. The address inputs must be stable before entering the
write cycle and must remain stable until CE or WE goes HIGH at
the end of the cycle. The data on the common I/O pins IO0-7 are
written into the memory if it is valid tSD before the end of a
WE-controlled write, or before the end of an CE-controlled write.
It is recommended that OE be kept HIGH during the entire write
cycle to avoid data bus contention on common I/O lines. If OE is
left LOW, internal circuitry turns off the output buffers tHZWE after
WE goes LOW.
The HSB signal is monitored by the system to detect if an
AutoStore cycle is in progress.
Hardware STORE (HSB) Operation
The CY14B256KA provides the HSB pin to control and
acknowledge the STORE operations. The HSB pin is used to
request a Hardware STORE cycle. When the HSB pin is driven
LOW, the CY14B256KA conditionally initiates a STORE
operation after tDELAY. An actual STORE cycle begins only if a
write to the SRAM has taken place since the last STORE or
RECALL cycle. The HSB pin also acts as an open drain driver
(internal 100 kΩ weak pull-up resistor) that is internally driven
LOW to indicate a busy condition when the STORE (initiated by
any means) is in progress.
AutoStore Operation
The CY14B256KA stores data to the nvSRAM using one of three
storage operations. These three operations are: Hardware
STORE, activated by the HSB; Software STORE, activated by
an address sequence; AutoStore, on device power-down. The
AutoStore operation is a unique feature of QuantumTrap
technology and is enabled by default on the CY14B256KA.
During normal operation, the device draws current from VCC to
charge a capacitor connected to the VCAP pin. This stored
charge is used by the chip to perform a single STORE operation.
If the voltage on the VCC pin drops below VSWITCH, the part
automatically disconnects the VCAP pin from VCC. A STORE
operation is initiated with power provided by the VCAP capacitor.
Note After each Hardware and Software STORE operation HSB
is driven HIGH for a short time (tHHHD) with standard output high
current and then remains HIGH by internal 100 kΩ pull-up
resistor.
SRAM write operations that are in progress when HSB is driven
LOW by any means are given time (tDELAY) to complete before
the STORE operation is initiated. However, any SRAM write
cycles requested after HSB goes LOW are inhibited until HSB
returns HIGH. In case the write latch is not set, HSB is not driven
LOW by the CY14B256KA. But any SRAM read and write cycles
are inhibited until HSB is returned HIGH by MPU or other
external source.
Note If the capacitor is not connected to VCAP pin, AutoStore
must be disabled using the soft sequence specified in Preventing
AutoStore on page 6. In case AutoStore is enabled without a
capacitor on VCAP pin, the device attempts an AutoStore
operation without sufficient charge to complete the Store. This
corrupts the data stored in nvSRAM.
Document #: 001-55720 Rev. *C
Page 4 of 27
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CY14B256KA
During any STORE operation, regardless of how it is initiated,
the CY14B256KA continues to drive the HSB pin LOW, releasing
it only when the STORE is complete. Upon completion of the
STORE operation, the nvSRAM memory access is inhibited for
The software sequence may be clocked with CE controlled reads
or OE controlled reads, with WE kept HIGH for all the six READ
sequences. After the sixth address in the sequence is entered,
the STORE cycle commences and the chip is disabled. HSB is
driven LOW. After the tSTORE cycle time is fulfilled, the SRAM is
activated again for the read and write operation.
t
LZHSB time after HSB pin returns HIGH. Leave the HSB uncon-
nected if it is not used.
Hardware RECALL (Power-Up)
Software RECALL
During power-up or after any low power condition
(VCC< VSWITCH), an internal RECALL request is latched. When
Data is transferred from the nonvolatile memory to the SRAM by
a software address sequence. A Software RECALL cycle is
initiated with a sequence of read operations in a manner similar
to the Software STORE initiation. To initiate the RECALL cycle,
the following sequence of CE or OE controlled read operations
must be performed:
VCC again exceeds the VSWITCH on powerup, a RECALL cycle
is automatically initiated and takes tHRECALL to complete. During
this time, the HSB pin is driven LOW by the HSB driver and all
reads and writes to nvSRAM are inhibited.
1. Read address 0x0E38 Valid READ
2. Read address 0x31C7 Valid READ
3. Read address 0x03E0 Valid READ
4. Read address 0x3C1F Valid READ
5. Read address 0x303F Valid READ
6. Read address 0x0C63 Initiate RECALL cycle
Software STORE
Data is transferred from the SRAM to the nonvolatile memory by
a software address sequence. The CY14B256KA Software
STORE cycle is initiated by executing sequential CE or OE
controlled read cycles from six specific address locations in
exact order. During the STORE cycle, an erase of the previous
nonvolatile data is first performed, followed by a program of the
nonvolatile elements. After a STORE cycle is initiated, further
input and output are disabled until the cycle is completed.
Internally, RECALL is a two step procedure. First, the SRAM data
is cleared. Next, the nonvolatile information is transferred into the
SRAM cells. After the tRECALL cycle time, the SRAM is again
ready for read and write operations. The RECALL operation
does not alter the data in the nonvolatile elements.
Because a sequence of reads from specific addresses is used
for STORE initiation, it is important that no other read or write
accesses intervene in the sequence, or the sequence is aborted
and no STORE or RECALL takes place.
To initiate the Software STORE cycle, the following read
sequence must be performed:
1. Read address 0x0E38 Valid READ
2. Read address 0x31C7 Valid READ
3. Read address 0x03E0 Valid READ
4. Read address 0x3C1F Valid READ
5. Read address 0x303F Valid READ
6. Read address 0x0FC0 Initiate STORE cycle
Document #: 001-55720 Rev. *C
Page 5 of 27
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CY14B256KA
Table 1. Mode Selection
[2]
Mode
I/O
Power
A14 - A0
CE
WE
OE
H
X
H
L
X
X
Not Selected
Read SRAM
Write SRAM
Output High Z
Output Data
Input Data
Standby
Active
L
L
L
L
X
L
X
X
Active
Active[3]
H
0x0E38
0x31C7
0x03E0
0x3C1F
0x303F
0x0B45
Read SRAM
Read SRAM
Read SRAM
Read SRAM
Read SRAM
AutoStore
Output Data
Output Data
Output Data
Output Data
Output Data
Output Data
Disable
L
L
L
H
H
H
L
L
L
0x0E38
0x31C7
0x03E0
0x3C1F
0x303F
0x0B46
Read SRAM
Read SRAM
Read SRAM
Read SRAM
Read SRAM
AutoStore Enable
Output Data
Output Data
Output Data
Output Data
Output Data
Output Data
Active[3]
Active ICC2
Active[3]
[3]
0x0E38
0x31C7
0x03E0
0x3C1F
0x303F
0x0FC0
Read SRAM
Read SRAM
Read SRAM
Read SRAM
Read SRAM
Nonvolatile
STORE
Output Data
Output Data
Output Data
Output Data
Output Data
Output High Z
0x0E38
0x31C7
0x03E0
0x3C1F
0x303F
0x0C63
Read SRAM
Read SRAM
Read SRAM
Read SRAM
Read SRAM
Nonvolatile
RECALL
Output Data
Output Data
Output Data
Output Data
Output Data
Output High Z
Preventing AutoStore
The AutoStore function is disabled by initiating an AutoStore
disable sequence. A sequence of read operations is performed
in a manner similar to the Software STORE initiation. To initiate
the AutoStore disable sequence, the following sequence of CE
or OE controlled read operations must be performed:
To initiate the AutoStore enable sequence, the following
sequence of CE or OE controlled read operations must be
performed:
1. Read address 0x0E38 Valid READ
2. Read address 0x31C7 Valid READ
3. Read address 0x03E0 Valid READ
4. Read address 0x3C1F Valid READ
5. Read address 0x303F Valid READ
6. Read address 0x0B46 AutoStore Enable
1. Read address 0x0E38 Valid READ
2. Read address 0x31C7 Valid READ
3. Read address 0x03E0 Valid READ
4. Read address 0x3C1F Valid READ
5. Read address 0x303F Valid READ
6. Read address 0x0B45 AutoStore Disable
If the AutoStore function is disabled or reenabled, a manual
STORE operation (Hardware or Software) issued to save the
AutoStore state through subsequent power-down cycles. The
part comes from the factory with AutoStore enabled.
The AutoStore is reenabled by initiating an AutoStore enable
sequence. A sequence of read operations is performed in a
manner similar to the Software RECALL initiation.
Notes
2. While there are 15 address lines on the CY14B256KA, only the lower 14 are used to control software modes.
3. The six consecutive address locations must be in the order listed. WE must be HIGH during all six cycles to enable a nonvolatile cycle.
Document #: 001-55720 Rev. *C
Page 6 of 27
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CY14B256KA
Setting the Clock
Data Protection
Setting the write bit ‘W’ (in the flags register at 0x7FF0) to a ‘1’
stops updates to the time keeping registers and enables the time
to be set. The correct day, date, and time is then written into the
registers and must be in 24-hour BCD format. The time written
is referred to as the “Base Time”. This value is stored in nonvol-
atile registers and used in the calculation of the current time.
Resetting the write bit to ‘0’ transfers the values of timekeeping
registers to the actual clock counters, after which the clock
resumes normal operation.
The CY14B256KA protects data from corruption during low
voltage conditions by inhibiting all externally initiated STORE
and write operations. The low voltage condition is detected when
VCC is less than VSWITCH. If the CY14B256KA is in a write mode
(both CE and WE are LOW) at power-up, after a RECALL or
STORE, the write is inhibited until the SRAM is enabled after
tLZHSB (HSB to output active). This protects against inadvertent
writes during power-up or brown out conditions.
If the time written to the timekeeping registers is not in the correct
BCD format, each invalid nibble of the RTC registers continue
counting to 0xF before rolling over to 0x0 after which RTC
resumes normal operation.
Noise Considerations
Refer to CY application note AN1064.
Real Time Clock Operation
nvTIME Operation
Note After ‘W’ bit is set to ‘0’, values written into the timekeeping,
alarm, calibration, and interrupt registers are transferred to the
RTC time keeping counters in tRTCp time. These counter values
must be saved to nonvolatile memory either by initiating a
Software/Hardware STORE or AutoStore operation. While
working in AutoStore disabled mode, perform a STORE
operation after tRTCp time while writing into the RTC registers for
the modifications to be correctly recorded.
The CY14B256KA offers internal registers that contain clock,
alarm, watchdog, interrupt, and control functions. Internal double
buffering of the clock and timer information registers prevents
accessing transitional internal clock data during a read or write
operation. Double buffering also circumvents disrupting normal
timing counts or the clock accuracy of the internal clock when
accessing clock data. Clock and alarm registers store data in
BCD format.
Backup Power
The RTC in the CY14B256KA is intended for permanently
powered operation. The VRTCcap or VRTCbat pin is connected
depending on whether a capacitor or battery is chosen for the
application. When the primary power, VCC, fails and drops below
VSWITCH the device switches to the backup power supply.
RTC functionality is described in the following sections. The RTC
register addresses for CY14B256KA range from 0x7FF0 to
0x7FFF. Refer to Table 3 on page 11 and Table 4 on page 12 for
a detailed Register Map description.
The clock oscillator uses very little current, which maximizes the
backup time available from the backup source. Regardless of the
clock operation with the primary source removed, the data stored
in the nvSRAM is secure, having been stored in the nonvolatile
elements when power was lost.
Clock Operations
The clock registers maintain time up to 9,999 years in one
second increments. The time can be set to any calendar time and
the clock automatically keeps track of days of the week and
month, leap years, and century transitions. There are eight
registers dedicated to the clock functions, which are used to set
time with a write cycle and to read time during a read cycle.
These registers contain the time of day in BCD format. Bits
defined as ‘0’ are currently not used and are reserved for future
use by Cypress.
During backup operation, the CY14B256KA consumes 0.35
microamps (Typical) at room temperature. The user must choose
capacitor or battery values according to the application.
Backup time values based on maximum current specifications
are shown in the following table. Nominal backup times are
approximately two times longer.
Reading the Clock
Table 2. RTC Backup Time
The double buffered RTC register structure reduces the chance
of reading incorrect data from the clock. Stop internal updates to
the CY14B256KA time keeping registers before reading clock
data, to prevent reading of data in transition. Stopping the
register updates does not affect clock accuracy.
Capacitor Value
0.1 F
Backup Time
72 hours
14 days
0.47 F
1.0 F
30 days
The updating process is stopped by writing a ‘1’ to the read bit
‘R’ (in the flags register at 0x7FF0), and does not restart until a
‘0’ is written to the read bit. The RTC registers are then read while
the internal clock continues to run. After a ‘0’ is written to the read
bit (‘R’), all RTC registers are simultaneously updated within
20 ms.
Using a capacitor has the obvious advantage of recharging the
backup source each time the system is powered up. If a battery
is used, a 3 V lithium is recommended and the CY14B256KA
sources current only from the battery when the primary power is
removed. However, the battery is not recharged at any time by
the CY14B256KA. The battery capacity must be chosen for total
anticipated cumulative down time required over the life of the
system.
Document #: 001-55720 Rev. *C
Page 7 of 27
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CY14B256KA
To determine the required calibration, the CAL bit in the flags
register (0x7FF0) must be set to ‘1’. This causes the INT pin to
toggle at a nominal frequency of 512 Hz. Any deviation
measured from the 512 Hz indicates the degree and direction of
the required correction. For example, a reading of 512.01024 Hz
indicates a +20 ppm error. Hence, a decimal value of –10
(001010b) must be loaded into the calibration register to offset
this error.
Stopping and Starting the Oscillator
The OSCEN bit in the calibration register at 0x7FF8 controls the
enable and disable of the oscillator. This bit is nonvolatile and is
shipped to customers in the “enabled” (set to ‘0’) state. To
preserve the battery life when the system is in storage, OSCEN
must be set to ‘1’. This turns off the oscillator circuit, extending
the battery life. If the OSCEN bit goes from disabled to enabled,
it takes approximately one second (two seconds maximum) for
the oscillator to start.
Note Setting or changing the calibration register does not affect
the test output frequency.
While system power is off, if the voltage on the backup supply
(VRTCcap or VRTCbat) falls below their respective minimum level,
the oscillator may fail.The CY14B256KA has the ability to detect
oscillator failure when system power is restored. This is recorded
in the oscillator fail bit (OSCF) of the flags register at the address
0x7FF0. When the device is powered on (VCC goes above
VSWITCH) the OSCEN bit is checked for “enabled” status. If the
OSCEN bit is enabled and the oscillator is not active within the
first 5 ms, the OSCF bit is set to ‘1’. The system must check for
this condition and then write ‘0’ to clear the flag. Note that in
addition to setting the OSCF flag bit, the time registers are reset
to the “Base Time” (see Setting the Clock on page 7), which is
the value last written to the timekeeping registers. The control or
calibration registers and the OSCEN bit are not affected by the
‘oscillator failed’ condition.
Reset the value of OSCF to ‘0’ when the time registers are written
for the first time. This initializes the state of this bit which may
have become set when the system was first powered on.
To reset OSCF, set the write bit ‘W’ (in the flags register at
0x7FF0) to a ‘1’ to enable writes to the Flag register. Write a ‘0’
to the OSCF bit and reset the write bit to ‘0’ to disable writes.
To set or clear CAL, set the write bit ‘W’ (in the flags register at
0x7FF0) to ‘1’ to enable writes to the flags register. Write a value
to CAL, and then reset the write bit to ‘0’ to disable writes.
Alarm
The alarm function compares user programmed values of alarm
time and date (stored in the registers 0x7FF1-5) with the corre-
sponding time of day and date values. When a match occurs, the
alarm internal flag (AF) is set and an interrupt is generated on
INT pin if alarm interrupt enable (AIE) bit is set.
There are four alarm match fields - date, hours, minutes, and
seconds. Each of these fields has a match bit that is used to
determine if the field is used in the alarm match logic. Setting the
match bit to ‘0’ indicates that the corresponding field is used in
the match process. Depending on the match bits, the alarm
occurs as specifically as once a month or as frequently as once
every minute. Selecting none of the match bits (all 1s) indicates
that no match is required and therefore, alarm is disabled.
Selecting all match bits (all 0s) causes an exact time and date
match.
Calibrating the Clock
There are two ways to detect an alarm event: by reading the AF
flag or monitoring the INT pin. The AF flag in the flags register at
0x7FF0 indicates that a date or time match has occurred. The
AF bit is set to ‘1’ when a match occurs. Reading the flags
register clears the alarm flag bit (and all others). A hardware
interrupt pin may also be used to detect an alarm event.
The RTC is driven by a quartz controlled crystal with a nominal
frequency of 32.768 kHz. Clock accuracy depends on the quality
of the crystal and calibration. The crystals available in market
typically have an error of +20 ppm to +35 ppm. However,
CY14B256KA employs a calibration circuit that improves the
accuracy to +1/–2 ppm at 25 °C. This implies an error of +2.5
seconds to -5 seconds per month.
To set, clear or enable an alarm, set the ‘W’ bit (in flags register
- 0x7FF0) to ‘1’ to enable writes to alarm registers. After writing
the alarm value, clear the ‘W’ bit back to ‘0’ for the changes to
take effect.
The calibration circuit adds or subtracts counts from the oscillator
divider circuit to achieve this accuracy. The number of pulses that
are suppressed (subtracted, negative calibration) or split (added,
positive calibration) depends upon the value loaded into the five
calibration bits found in calibration register at 0x7FF8. The
calibration bits occupy the five lower order bits in the calibration
register. These bits are set to represent any value between ‘0’
and 31 in binary form. Bit D5 is a sign bit, where a ‘1’ indicates
positive calibration and a ‘0’ indicates negative calibration.
Adding counts speeds the clock up and subtracting counts slows
the clock down. If a binary ‘1’ is loaded into the register, it corre-
sponds to an adjustment of 4.068 or –2.034 ppm offset in oscil-
lator error, depending on the sign.
Note CY14B256KA requires the alarm match bit for seconds
(0x7FF2 - D7) to be set to ‘0’ for proper operation of alarm flag
and interrupt.
Watchdog Timer
The watchdog timer is a free running down counter that uses the
32 Hz clock (31.25 ms) derived from the crystal oscillator. The
oscillator must be running for the watchdog to function. It begins
counting down from the value loaded in the watchdog timer
register.
The timer consists of a loadable register and a free running
counter. On power-up, the watchdog time out value in register
0x7FF7 is loaded into the counter load register. Counting begins
on power-up and restarts from the loadable value any time the
watchdog strobe (WDS) bit is set to ‘1’. The counter is compared
to the terminal value of ‘0’. If the counter reaches this value, it
causes an internal flag and an optional interrupt output. You can
prevent the time out interrupt by setting WDS bit to ‘1’ prior to the
counter reaching ‘0’. This causes the counter to reload with the
Calibration occurs within a 64-minute cycle. The first 62 minutes
in the cycle may, once per minute, have one second shortened
by 128 or lengthened by 256 oscillator cycles. If a binary ‘1’ is
loaded into the register, only the first two minutes of the
64-minute cycle are modified. If a binary 6 is loaded, the first 12
are affected, and so on. Therefore, each calibration step has the
effect of adding 512 or subtracting 256 oscillator cycles for every
125,829,120 actual oscillator cycles, that is, 4.068 or –2.034 ppm
of adjustment per calibration step in the calibration register.
Document #: 001-55720 Rev. *C
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CY14B256KA
watchdog time out value and to be restarted. As long as the user
sets the WDS bit prior to the counter reaching the terminal value,
the interrupt and WDT flag never occur.
Interrupts
The CY14B256KA has flags register, interrupt register and
interrupt logic that can signal interrupt to the microcontroller.
There are three potential sources for interrupt: watchdog timer,
power monitor, and alarm timer. Each of these can be individually
enabled to drive the INT pin by appropriate setting in the interrupt
register (0x7FF6). In addition, each has an associated flag bit in
the flags register (0x7FF0) that the host processor uses to
determine the cause of the interrupt. The INT pin driver has two
bits that specify its behavior when an interrupt occurs.
New time out values are written by setting the watchdog write bit
to ‘0’. When the WDW is ‘0’, new writes to the watchdog time out
value bits D5-D0 are enabled to modify the time out value. When
WDW is ‘1’, writes to bits D5-D0 are ignored. The WDW function
enables a user to set the WDS bit without concern that the
watchdog timer value is modified. A logical diagram of the
watchdog timer is shown in Figure 3. Note that setting the
watchdog time out value to ‘0’ disables the watchdog function.
An interrupt is raised only if both a flag is raised by one of the
three sources and the respective interrupt enable bit in interrupts
register is enabled (set to ‘1’). After an interrupt source is active,
two programmable bits, H/L and P/L, determine the behavior of
the output pin driver on INT pin. These two bits are located in the
interrupt register and can be used to drive level or pulse mode
output from the INT pin. In pulse mode, the pulse width is
internally fixed at approximately 200 ms. This mode is intended
to reset a host microcontroller. In the level mode, the pin goes to
its active polarity until the flags register is read by the user. This
mode is used as an interrupt to a host microcontroller. The
control bits are summarized in the following section.
The output of the watchdog timer is the flag bit WDF that is set if
the watchdog is allowed to time out. If the watchdog interrupt
enable (WIE) bit in the interrupt register is set, a hardware
interrupt on INT pin is also generated on watchdog timeout. The
flag and the hardware interrupt are both cleared when user reads
the flags register.
.
Figure 3. Watchdog Timer Block Diagram
Clock
Oscillator
1 Hz
Divider
Interrupts are only generated while working on normal power and
are not triggered when system is running in backup power mode.
32,768 KHz
32 Hz
Zero
Compare
WDF
Counter
Note CY14B256KA generates valid interrupts only after the
Powerup RECALL sequence is completed. All events on INT pin
must be ignored for tHRECALL duration after powerup.
Load
Interrupt Register
WDS
Register
Watchdog Interrupt Enable (WIE). When set to ‘1’, the
watchdog timer drives the INT pin and an internal flag when a
watchdog time out occurs. When WIE is set to ‘0’, the watchdog
timer only affects the WDF flag in flags register.
Q
D
WDW
Q
Watchdog
Register
Alarm Interrupt Enable (AIE). When set to ‘1’, the alarm match
drives the INT pin and an internal flag. When AIE is set to ‘0’, the
alarm match only affects the AF flag in flags register.
write to
Watchdog
Register
Power Fail Interrupt Enable (PFE). When set to ‘1’, the power
fail monitor drives the pin and an internal flag. When PFE is set
to ‘0’, the power fail monitor only affects the PF flag in flags
register.
Power Monitor
The CY14B256KA provides a power management scheme with
power fail interrupt capability. It also controls the internal switch
to backup power for the clock and protects the memory from low
High/Low (H/L). When set to a ‘1’, the INT pin is active HIGH
and the driver mode is push pull. The INT pin drives high only
when VCC is greater than VSWITCH. When set to a ‘0’, the INT pin
is active LOW and the drive mode is open drain. The INT pin
must be pulled up to Vcc by a 10 k resistor while using the
interrupt in active LOW mode.
VCC access. The power monitor is based on an internal band gap
reference circuit that compares the VCC voltage to VSWITCH
threshold.
As described in the AutoStore Operation on page 4, when
VSWITCH is reached as VCC decays from power loss, a data
STORE operation is initiated from SRAM to the nonvolatile
elements, securing the last SRAM data state. Power is also
switched from VCC to the backup supply (battery or capacitor) to
operate the RTC oscillator.
Pulse/Level (P/L). When set to a ‘1’ and an interrupt occurs, the
INT pin is driven for approximately 200 ms. When P/L is set to a
‘0’, the INT pin is driven high or low (determined by H/L) until the
flags register is read.
When an enabled interrupt source activates the INT pin, an
external host reads the flags register to determine the cause. All
flags are cleared when the register is read. If the INT pin is
programmed for level mode, then the condition clears and the
INT pin returns to its inactive state. If the pin is programmed for
pulse mode, then reading the flag also clears the flag and the pin.
The pulse does not complete its specified duration if the flags
register is read. If the INT pin is used as a host reset, then the
flags register is not read during a reset.
When operating from the backup source, read and write opera-
tions to nvSRAM are inhibited and the RTC functions are not
available to the user. The RTC clock continues to operate in the
background. The updated RTC time keeping registers data are
available to the user after VCC is restored to the device (see
AutoStore/Power-Up RECALL on page 20).
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CY14B256KA
Flags Register
The flags register has three flag bits: WDF, AF, and PF, which can be used to generate an interrupt. These flags are set by the watchdog
timeout, alarm match, or power fail monitor respectively. The processor can either poll this register or enable interrupts to be informed
when a flag is set. These flags are automatically reset when the register is read. The flags register is automatically loaded with the
value 0x00 on power-up (except for the OSCF bit; see Stopping and Starting the Oscillator on page 8).
Figure 4. RTC Recommended Component Configuration
Recommended Values
Y
= 32.768 KHz (12.5 pF)
1
C1 = 10 pF
C2 = 67 pF
Note: The recommended values for C1 and C2 include
board trace capacitance.
C1
C2
X
out
Y1
X
in
Figure 5. Interrupt Block Diagram
WDF
WDF - Watchdog Timer Flag
WIE - Watchdog Interrupt
Enable
Watchdog
Timer
WIE
PF
PF - Power Fail Flag
PFE - Power Fail Enable
V
CC
P/L
AF - Alarm Flag
Power
Pin
Driver
AIE - Alarm Interrupt Enable
Monitor
INT
PFE
P/L - Pulse Level
H/L - High/Low
VINT
H/L
V
SS
AF
Clock
Alarm
AIE
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CY14B256KA
Table 3. RTC Register Map[4, 5]
Register
BCD Format Data[4]
Function/Range
CY14B256KA
0x7FFF
D7
D6
D5
D4
D3
D2
D1
Years
Months
D0
10s years
Years: 00–99
0x7FFE
0
0
0
10s
Months: 01–12
months
0x7FFD
0x7FFC
0x7FFB
0x7FFA
0x7FF9
0x7FF8
0
0
0
0
0
0
0
0
10s day of month
Day of month
Day of week
Day of month: 01–31
Day of week: 01–07
Hours: 00–23
0
0
0
10s hours
Hours
Minutes
Seconds
10s minutes
10s seconds
Minutes: 00–59
Seconds: 00–59
Calibration values [6]
OSCEN
(0)
0
Cal
sign (0)
Calibration (00000)
0x7FF7
WDS (0)
WDW
(0)
WDT (000000)
Watchdog [6]
0x7FF6
0x7FF5
0x7FF4
0x7FF3
0x7FF2
0x7FF1
0x7FF0
WIE (0) AIE (0) PFE (0)
0
H/L (1) P/L (0)
0
0
Interrupts [6]
Alarm, Day of month: 01–31
Alarm, hours: 00–23
Alarm, minutes: 00–59
Alarm, seconds: 00–59
Centuries: 00–99
M (1)
M (1)
M (1)
M (1)
0
0
10s alarm date
10s alarm hours
Alarm day
Alarm hours
Alarm minutes
Alarm, seconds
Centuries
10 alarm minutes
10 alarm seconds
10s centuries
AF PF
WDF
OSCF [7]
0
CAL
(0)
W (0)
R (0)
Flags [6]
Notes
4. The unused bits of RTC registers are reserved for future use and should be set to ‘0’.
5. ( ) designates values shipped from the factory.
6. This is a binary value, not a BCD value.
7. When the user resets OSCF flag bit, the flags register will be updated after t
time.
RTCp
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CY14B256KA
Table 4. Register Map Detail
Register
Description
CY14B256KA
Time Keeping - Years
0x7FFF
D7
D6
D5
10s years
D4
D3
D2
D1
D0
Years
Contains the lower two BCD digits of the year. Lower nibble (four bits) contains the value for years; upper nibble
(four bits) contains the value for 10s of years. Each nibble operates from 0 to 9. The range for the register is 0–99.
Time Keeping - Months
0x7FFE
0x7FFD
D7
D6
D5
D4
D3
D2
D1
D0
0
0
0
10s month
Months
Contains the BCD digits of the month. Lower nibble (four bits) contains the lower digit and operates from 0 to 9;
upper nibble (one bit) contains the upper digit and operates from 0 to 1. The range for the register is 1–12.
Time Keeping - Date
D7
D6
D5
D4
D3
D2
D1
D0
0
0
10s day of month
Day of month
Contains the BCD digits for the date of the month. Lower nibble (four bits) contains the lower digit and operates
from 0 to 9; upper nibble (two bits) contains the 10s digit and operates from 0 to 3. The range for the register is
1–31. Leap years are automatically adjusted for.
Time Keeping - Day
0x7FFC
0x7FFB
0x7FFA
0x7FF9
D7
D6
D5
D4
D3
D2
D1
D0
0
0
0
0
0
Day of week
Lower nibble (three bits) contains a value that correlates to day of the week. Day of the week is a ring counter
that counts from 1 to 7 then returns to 1. The user must assign meaning to the day value, because the day is not
integrated with the date.
Time Keeping - Hours
D7
D6
D5
D4
D3
D2
D1
D0
0
0
10s hours
Hours
Contains the BCD value of hours in 24 hour format. Lower nibble (four bits) contains the lower digit and operates
from 0 to 9; upper nibble (two bits) contains the upper digit and operates from 0 to 2. The range for the register
is 0–23.
Time Keeping - Minutes
D7
D6
D5
D4
D3
D2
D1
D0
0
10s minutes
Minutes
Contains the BCD value of minutes. Lower nibble (four bits) contains the lower digit and operates from 0 to 9;
upper nibble (three bits) contains the upper minutes digit and operates from 0 to 5. The range for the register is
0–59.
Time Keeping - Seconds
D7
D6
D5
D4
D3
D2
D1
D0
0
10s seconds
Seconds
Contains the BCD value of seconds. Lower nibble (four bits) contains the lower digit and operates from 0 to 9;
upper nibble (three bits) contains the upper digit and operates from 0 to 5. The range for the register is 0–59.
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CY14B256KA
Table 4. Register Map Detail (continued)
Register
Description
CY14B256KA
Calibration/Control
0x7FF8
D7
D6
D5
D4
D3
D2
D1
D0
OSCEN
0
Calibration
sign
Calibration
OSCEN
Oscillator Enable. When set to ‘1’, the oscillator is stopped. When set to ‘0’, the oscillator runs. Disabling the
oscillator saves battery or capacitor power during storage.
Calibration
Sign
Determines if the calibration adjustment is applied as an addition (1) to or as a subtraction (0) from the time-base.
Calibration
These five bits control the calibration of the clock.
WatchDog Timer
0x7FF7
D7
D6
D5
D4
D3
D2
D1
D0
WDS
WDW
WDT
WDS
Watchdog strobe. Setting this bit to ‘1’ reloads and restarts the watchdog timer. Setting the bit to ‘0’ has no effect.
The bit is cleared automatically after the watchdog timer is reset. The WDS bit is write only. Reading it always
returns a 0.
WDW
Watchdog write enable. Setting this bit to ‘1’ disables any WRITE to the watchdog timeout value (D5–D0). This
allows the user to set the watchdog strobe bit without disturbing the timeout value. Setting this bit to ‘0’ allows
bits D5–D0 to be written to the watchdog register when the next write cycle is complete. This function is explained
in more detail in Watchdog Timer on page 8.
WDT
Watchdog timeout selection. The watchdog timer interval is selected by the 6-bit value in this register. It repre-
sents a multiplier of the 32 Hz count (31.25 ms). The range of timeout value is 31.25 ms (a setting of 1) to 2
seconds (setting of 3 Fh). Setting the watchdog timer register to 0 disables the timer. These bits can be written
only if the WDW bit was set to 0 on a previous cycle.
Interrupt Status/Control
0x7FF6
D7
D6
D5
D4
D3
D2
D1
D0
WIE
AIE
PFE
0
H/L
P/L
0
0
WIE
AIE
Watchdog interrupt enable. When set to ‘1’ and a watchdog timeout occurs, the watchdog timer drives the INT
pin and the WDF flag. When set to ‘0’, the watchdog timeout affects only the WDF flag.
Alarm interrupt enable. When set to ‘1’, the alarm match drives the INT pin and the AF flag. When set to ‘0’, the
alarm match only affects the AF flag.
PFE
Power fail enable. When set to ‘1’, the power fail monitor drives the INT pin and the PF flag. When set to ‘0’, the
power fail monitor affects only the PF flag.
0
Reserved for future use
H/L
P/L
High/Low. When set to ‘1’, the INT pin is driven active HIGH. When set to ‘0’, the INT pin is open drain, active LOW.
Pulse/Level. When set to ‘1’, the INT pin is driven active (determined by H/L) by an interrupt source for approx-
imately 200 ms. When set to ‘0’, the INT pin is driven to an active level (as set by H/L) until the flags register is read.
Alarm - Day
0x7FF5
D7
D6
D5
D4
D3
D2
D1
Alarm date
D0
M
0
10s alarm date
Contains the alarm value for the date of the month and the mask bit to select or deselect the date value.
M
Match. When this bit is set to ‘0’, the date value is used in the alarm match. Setting this bit to ‘1’ causes the match
circuit to ignore the date value.
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CY14B256KA
Table 4. Register Map Detail (continued)
Register
Description
CY14B256KA
Alarm - Hours
0x7FF4
D7
D6
D5
D4
D3
D2
D1
D0
M
0
10s alarm hours
Alarm hours
Contains the alarm value for the hours and the mask bit to select or deselect the hours value.
M
Match. When this bit is set to ‘0’, the hours value is used in the alarm match. Setting this bit to ‘1’ causes the
match circuit to ignore the hours value.
Alarm - Minutes
0x7FF3
D7
D6
D5
D4
D3
D2
D1
D0
M
10s alarm minutes
Alarm minutes
Contains the alarm value for the minutes and the mask bit to select or deselect the minutes value.
M
Match. When this bit is set to ‘0’, the minutes value is used in the alarm match. Setting this bit to ‘1’ causes the
match circuit to ignore the minutes value.
Alarm - Seconds
0x7FF2
D7
D6
D5
D4
D3
D2
D1
D0
M
10s alarm seconds
Alarm seconds
Contains the alarm value for the seconds and the mask bit to select or deselect the seconds’ value.
M
Match. When this bit is set to ‘0’, the seconds value is used in the alarm match. Setting this bit to ‘1’ causes the
match circuit to ignore the seconds value.
Time Keeping - Centuries
0x7FF1
D7
D6
D5
10s centuries
D4
D3
D2
D1
Centuries
D0
Contains the BCD value of centuries. Lower nibble (four bits) contains the lower digit and operates from 0 to 9;
upper nibble (four bits) contains the upper digit and operates from 0 to 9. The range for the register is 0-99
centuries.
Flags
0x7FF0
D7
D6
D5
D4
D3
D2
D1
D0
WDF
AF
PF
OSCF
0
CAL
W
R
WDF
AF
Watchdog timer flag. This read only bit is set to ‘1’ when the watchdog timer is allowed to reach 0 without being
reset by the user. It is cleared to ‘0’ when the flags register is read or on power-up
Alarm flag. This read only bit is set to ‘1’ when the time and date match the values stored in the alarm registers
with the match bits = 0. It is cleared when the flags register is read or on power-up.
PF
Power fail flag. This read only bit is set to 1 when power falls below the power fail threshold VSWITCH. It is cleared
to 0 when the flags register is read or on power-up.
OSCF
Oscillator fail flag. Set to ‘1’ on power-up if the oscillator is enabled and not running in the first 5 ms of operation.
This indicates that RTC backup power failed and clock value is no longer valid. This bit survives the power cycle
and is never cleared internally by the chip. The user must check for this condition and write '0' to clear this flag.
When user resets OSCF flag bit, the bit will be updated after tRTCp time.
CAL
W
Calibration mode. When set to ‘1’, a 512 Hz square wave is output on the INT pin. When set to ‘0’, the INT pin
resumes normal operation. This bit defaults to 0 (disabled) on power-up.
Write enable: Setting the ‘W’ bit to ‘1’ freezes updates of the RTC registers. The user can then write to RTC
registers, alarm registers, calibration register, interrupt register and flags register. Setting the ‘W’ bit to ‘0’ causes
the contents of the RTC registers to be transferred to the time keeping counters if the time has changed. This
transfer process takes tRTCp time to complete. This bit defaults to 0 on power-up.
R
Read enable: Setting ‘R’ bit to ‘1’, stops clock updates to user RTC registers so that clock updates are not seen
during the reading process. Set ‘R’ bit to ‘0’ to resume clock updates to the holding register. Setting this bit does
not require ‘W’ bit to be set to ‘1’. This bit defaults to 0 on power-up.
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CY14B256KA
■ Power-up boot firmware routines should rewrite the nvSRAM
into the desired state (for example, AutoStore enabled). While
the nvSRAM is shipped in a preset state, best practice is to
again rewrite the nvSRAM into the desired state as a safeguard
against events that might flip the bit inadvertently such as
program bugs and incoming inspection routines.
Best Practices
nvSRAM products have been used effectively for over 27 years.
While ease-of-use is one of the product’s main system values,
experience gained working with hundreds of applications has
resulted in the following suggestions as best practices:
■ The VCAP value specified in this data sheet includes a minimum
and a maximum value size. Best practice is to meet this
requirement and not exceed the maximum VCAP value because
the nvSRAM internal algorithm calculates VCAP charge and
discharge time based on this max VCAP value. Customers that
want to use a larger VCAP value to make sure there is extra store
charge and store time should discuss their VCAP size selection
with Cypress to understand any impact on the VCAP voltage level
at the end of a tRECALL period.
■ The nonvolatile cells in this nvSRAM product are delivered from
Cypress with 0x00 written in all cells. Incoming inspection
routines at customer or contract manufacturer’s sites
sometimes reprogram these values. Final NV patterns are
typically repeating patterns of AA, 55, 00, FF, A5, or 5A. End
product’s firmware should not assume an NV array is in a set
programmed state. Routines that check memory content
values to determine first time system configuration, cold or
warm boot status, and so on should always program a unique
NV pattern (that is, complex 4-byte pattern of 46 E6 49 53 hex
or more random bytes) as part of the final system manufac-
turing test to ensure these system routines work consistently.
■ When base time is updated, these updates are transferred to
the time keeping registers when ‘W’ bit is set to ‘0’. This transfer
takes tRTCp time to complete. It is recommended to initiate
software STORE or Hardware STORE after tRTCp time to save
the base time into nonvolatile memory.
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CY14B256KA
Package power dissipation
capability (TA = 25 °C) .................................................. 1.0 W
Maximum Ratings
Exceeding maximum ratings may shorten the useful life of the
device. These user guidelines are not tested.
Surface mount Pb soldering
temperature (3 seconds) .......................................... +260 °C
Storage temperature ................................ –65 °C to +150 °C
Maximum accumulated storage time
DC output current (1 output at a time, 1s duration)..... 15 mA
Static discharge voltage.......................................... > 2001 V
(per MIL-STD-883, Method 3015)
At 150 °C ambient temperature........................1000 h
At 85 °C ambient temperature..................... 20 Years
Ambient temperature with power applied ...–55 °C to +150 C
Supply voltage on VCC relative to VSS............–0.5 V to 4.1 V
Latch up current..................................................... > 200 mA
Operating Range
Range
Industrial
Ambient Temperature
VCC
Voltage applied to outputs
in High Z state .....................................–0.5 V to VCC + 0.5 V
–40 °C to +85 °C
2.7 V to 3.6 V
Input voltage.........................................–0.5 V to Vcc + 0.5 V
Transient voltage (<20 ns) on
any pin to ground potential ..................–2.0 V to VCC + 2.0 V
DC Electrical Characteristics
Over the Operating Range (VCC = 2.7 V to 3.6 V)
Parameter
VCC
Description
Test Conditions
Min Typ[8] Max Unit
Power supply voltage
2.7
–
3.0
–
3.6
V
ICC1
Average Vcc current tRC = 25 ns
70
52
mA
mA
t
RC = 45 ns
Values obtained without output loads (IOUT = 0 mA)
ICC2
Average VCC current All inputs don’t care, VCC = Max.
during STORE Average current for duration tSTORE
–
–
–
10
–
mA
mA
[8]
Average VCC current All inputs cycling at CMOS levels.
at tRC= 200 ns, Values obtained without output loads (IOUT = 0 mA).
CC (Typ), 25 °C
35
ICC3
V
ICC4
Average VCAP current All inputs don’t care. Average current for duration tSTORE
during AutoStore
cycle
–
–
–
–
5
5
mA
mA
ISB
VCC standby current CE > (VCC – 0.2 V). VIN < 0.2 V or > (VCC – 0.2 V). W bit set to ‘0’.
Standby current level after nonvolatile cycle is complete.
Inputs are static. f = 0 MHz.
[9]
Input leakage current VCC = Max, VSS < VIN < VCC
(except HSB)
–1
–100
–1
–
–
–
–
–
+1
+1
+1
µA
µA
µA
V
IIX
Input leakage current VCC = Max, VSS < VIN < VCC
(for HSB)
IOZ
VIH
VIL
Off state output
leakage current
VCC = Max, VSS < VOUT < VCC, CE or OE > VIH or WE < VIL
Input HIGH voltage
2.0
VCC
0.5
+
Input LOW voltage
VSS
0.5
–
0.8
V
VOH
VOL
Output HIGH voltage IOUT = –2 mA
Output LOW voltage IOUT = 4 mA
2.4
–
–
–
–
V
V
0.4
Storage capacitor
Between VCAP pin and VSS, 5 V rated
61
68
180
µF
VCAP
Notes
8. Typical values are at 25 °C, V = V (Typ). Not 100% tested.
CC
CC
9. The HSB pin has I
= -2 uA for V of 2.4 V when both active HIGH and low drivers are disabled. When they are enabled standard V and V are valid. This
OUT
O
H
O
H
O
L
parameter is characterized but not tested.
Document #: 001-55720 Rev. *C
Page 16 of 27
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CY14B256KA
Data Retention and Endurance
Parameter
Description
Min
20
Unit
Years
K
DATAR
NVC
Data retention
Nonvolatile STORE operations
1,000
Capacitance
Parameter[10]
Description
Test Conditions
TA = 25 °C, f = 1 MHz,
CC = VCC (Typ)
Max
7
Unit
pF
CIN
Input capacitance
Output capacitance
V
COUT
7
pF
Thermal Resistance
Parameter[10]
Description
Test Conditions
48 SSOP
Unit
ΘJA
Thermal resistance
(Junction to ambient)
Test conditions follow standard test methods
and procedures for measuring thermal
37.47
°C/W
impedance, in accordance with EIA/JESD51.
ΘJC
Thermal resistance
(Junction to case)
24.71
°C/W
Figure 6. AC Test Loads
577 Ω
577 Ω
R1
3.0 V
3.0 V
OUTPUT
R1
OUTPUT
R2
789 Ω
R2
789 Ω
5 pF
30 pF
AC Test Conditions
Input pulse levels....................................................0 V to 3 V
Input rise and fall times (10% - 90%)............................ <3 ns
Input and output timing reference levels........................ 1.5V
RTC Characteristics
Parameter
VRTCbat
IBAK
Description
Min
1.8
–
Typ[11]
Max
Units
V
RTC battery pin voltage
RTC backup current
3.0
–
3.6
0.35
–
[12]
TA (Min)
25 °C
µA
µA
µA
V
–
0.35
–
TA (Max)
TA (Min)
25 °C
–
0.5
3.6
3.6
3.6
2
[13]
VRTCcap
RTC capacitor pin voltage
1.6
1.5
1.4
–
–
3.0
–
V
TA (Max)
V
tOCS
RTC oscillator time to start
1
sec
μs
Ω
tRTCp
RBKCHG
RTC processing time from end of ‘W’ bit set to ‘0’
RTC backup capacitor charge current-limiting resistor
–
–
350
850
350
–
–
Notes
10. These parameters are guaranteed by design and are not tested.
11. Typical values are at 25 °C, V = V (Typ). Not 100% tested.
CC
CC
12. From either V
or V
RTCcap
RTCbat.
13. If V
> 0.5 V or if no capacitor is connected to V
pin, the oscillator starts in tOCS time. If a backup capacitor is connected and V < 0.5 V, the capacitor
RTCcap
RTCcap
RTCcap
must be allowed to charge to 0.5 V for oscillator to start.
Document #: 001-55720 Rev. *C
Page 17 of 27
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CY14B256KA
AC Switching Characteristics
Parameters
25 ns
45 ns
Unit
Description
Cypress
Alt
Min
Max
Min
Max
Parameter
Parameter
SRAM Read Cycle
tACE
tACS
Chip enable access time
–
25
–
–
45
–
ns
ns
[14]
tRC
tAA
tOE
tOH
tLZ
Read cycle time
25
45
tRC
[15]
Address access time
–
–
3
3
–
0
–
0
–
25
12
–
–
–
3
3
–
0
–
0
–
45
20
–
ns
ns
ns
ns
ns
ns
ns
ns
ns
tAA
Output enable to data valid
Output hold after address change
Chip enable to output active
Chip disable to output Inactive
Output enable to output active
Output disable to output inactive
Chip enable to power active
Chip disable to power standby
tDOE
[15]
tOHA
[16, 17]
[16, 17]
[16, 17]
[16, 17]
–
–
tLZCE
tHZCE
tLZOE
tHZOE
tHZ
10
–
15
–
tOLZ
tOHZ
tPA
10
–
15
–
[16]
tPU
[16]
tPS
25
45
tPD
SRAM Write Cycle
tWC
tPWE
tSCE
tSD
tWC
Write cycle time
25
20
20
10
0
–
–
45
30
30
15
0
–
–
ns
ns
ns
ns
ns
ns
ns
ns
ns
tWP
tCW
tDW
tDH
tAW
tAS
Write pulse width
Chip enable to end of write
Data setup to end of write
Data hold after end of write
Address setup to end of write
Address setup to start of write
Address hold after end of write
Write enable to output disable
–
–
–
–
tHD
–
–
tAW
tSA
20
0
–
30
0
–
–
–
tHA
tWR
tWZ
0
–
0
–
[16, 17, 18]
[16, 17]
–
10
–
15
tHZWE
tLZWE
tOW
Output active after end of write
3
–
3
–
ns
Switching Waveforms
Address
Figure 7. SRAM Read Cycle #1: Address Controlled [14, 15, 19]
tRC
Address Valid
tAA
Output Data Valid
Previous Data Valid
tOHA
Data Output
Notes
14. WE must be HIGH during SRAM read cycles.
15. Device is continuously selected with CE and OE LOW.
16. These parameters are guaranteed by design and are not tested.
17. Measured ±200 mV from steady state output voltage.
18. If WE is low when CE goes low, the outputs remain in the high impedance state.
19. HSB must remain HIGH during Read and Write cycles.
Document #: 001-55720 Rev. *C
Page 18 of 27
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CY14B256KA
Figure 8. SRAM Read Cycle #2: CE and OE Controlled [20, 21]
Address
CE
Address Valid
tRC
tHZCE
tACE
tAA
tLZCE
tHZOE
tDOE
OE
tLZOE
High Impedance
Standby
Data Output
Output Data Valid
tPU
tPD
Active
ICC
Figure 9. SRAM Write Cycle #1: WE Controlled [21, 22, 23]
tWC
Address
CE
Address Valid
tSCE
tHA
tAW
tPWE
WE
Data Input
Data Output
tSA
tHD
tSD
Input Data Valid
tLZWE
tHZWE
High Impedance
Previous Data
Figure 10. SRAM Write Cycle #2: CE Controlled [21, 22, 23]
tWC
Address Valid
Address
tSA
tSCE
tHA
CE
tPWE
WE
tHD
tSD
Input Data Valid
Data Input
High Impedance
Data Output
Note
20. WE must be HIGH during SRAM read cycles.
21. HSB must remain HIGH during Read and Write cycles.
22. If WE is low when CE goes low, the outputs remain in the high impedance state.
23. CE or WE must be >V during address transitions.
IH
Document #: 001-55720 Rev. *C
Page 19 of 27
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CY14B256KA
AutoStore/Power-Up RECALL
Parameter
Description
Min
Max
Unit
[24]
Power-Up RECALL duration
STORE cycle duration
–
20
ms
tHRECALL
[25]
–
–
8
25
ms
ns
V
tSTORE
tDELAY
[26]
Time allowed to complete SRAM write cycle
Low voltage trigger level
VCC rise time
–
2.65
–
VSWITCH
[27]
150
–
µs
V
tVCCRISE
[27]
HSB output disable voltage
1.9
VHDIS
[27]
tLZHSB
HSB to output active time
HSB high active time
–
–
5
µs
ns
[27]
tHHHD
500
Switching Waveforms
Figure 11. AutoStore or Power-Up RECALL [28]
VCC
VSWITCH
VHDIS
25
25
tVCCRISE
tSTORE
tSTORE
Note
Note
tHHHD
tHHHD
29
29
Note
Note
HSB OUT
AutoStore
tDELAY
tLZHSB
tLZHSB
tDELAY
POWER-
UP
RECALL
tHRECALL
tHRECALL
Read & Write
Inhibited
(RWI)
Read & Write
Read & Write
POWER-UP
RECALL
BROWN
OUT
AutoStore
POWER
DOWN
AutoStore
POWER-UP
RECALL
Notes
24. t
starts from the time V rises above V
SWITCH.
HRECALL
CC
25. If an SRAM write has not taken place since the last nonvolatile cycle, no AutoStore or Hardware STORE takes place
26. On a Hardware STORE and AutoStore initiation, SRAM write operation continues to be enabled for time t
27. These parameters are guaranteed by design and are not tested.
.
DELAY
28. Read and Write cycles are ignored during STORE, RECALL, and while V is below V
CC
SWITCH.
29. During power-up and power-down, HSB glitches when HSB pin is pulled up through an external resistor.
Document #: 001-55720 Rev. *C
Page 20 of 27
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CY14B256KA
Software Controlled STORE/RECALL Cycle
25 ns
45 ns
Unit
Parameter[30, 31]
tRC
tSA
tCW
tHA
Description
Min
25
0
20
0
Max
–
–
–
–
Min
45
0
30
0
Max
STORE/RECALL initiation cycle time
Address setup time
–
–
ns
ns
ns
ns
µs
µs
Clock pulse width
Address hold time
RECALL duration
–
–
tRECALL
–
–
200
100
–
–
200
100
[32, 33]
Soft sequence processing time
tSS
Switching Waveforms
Figure 12. CE & OE Controlled Software STORE/RECALL Cycle [31]
tRC
tRC
Address
Address #1
tCW
Address #6
tCW
tSA
CE
tSA
tHA
tHA
tHA
tHA
OE
tHHHD
tHZCE
HSB (STORE only)
DQ (DATA)
34
Note
tDELAY
tLZCE
tLZHSB
High Impedance
tSTORE/tRECALL
RWI
Figure 13. AutoStore Enable/Disable Cycle
tRC
tRC
Address
Address #1
Address #6
tCW
tSA
tCW
CE
tSA
tHA
tHA
tHA
tHA
OE
tSS
tHZCE
34
Note
tLZCE
tDELAY
DQ (DATA)
Notes
30. The software sequence is clocked with CE controlled or OE controlled reads.
31. The six consecutive addresses must be read in the order listed in Table 1. WE must be HIGH during all six consecutive cycles.
32. This is the amount of time it takes to take action on a soft sequence command. Vcc power must remain HIGH to effectively register command.
33. Commands such as STORE and RECALL lock out I/O until operation is complete which further increases this time. See the specific command.
34. DQ output data at the sixth read may be invalid since the output is disabled at t
time.
DELAY
Document #: 001-55720 Rev. *C
Page 21 of 27
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CY14B256KA
Hardware STORE Cycle
Parameter
Description
Min
–
Max
25
–
Unit
ns
tDHSB
tPHSB
HSB to output active time when write latch not set
Hardware STORE pulse width
15
ns
Switching Waveforms
Figure 14. Hardware STORE Cycle[35]
Write latch set
tPHSB
HSB (IN)
tSTORE
tHHHD
tDELAY
HSB (OUT)
DQ (Data Out)
RWI
tLZHSB
Write latch not set
tPHSB
HSB pin is driven high to VCC only by Internal
100 kOhm resistor,
HSB (IN)
HSB driver is disabled
SRAM is disabled as long as HSB (IN) is driven low.
tDELAY
tDHSB
tDHSB
HSB (OUT)
RWI
Figure 15. Soft Sequence Processing[36, 37]
tSS
tSS
Soft Sequence
Command
Soft Sequence
Command
Address
Address #1
tSA
Address #6
tCW
Address #1
Address #6
tCW
CE
VCC
Note
35. If an SRAM write has not taken place since the last nonvolatile cycle, no AutoStore or Hardware STORE takes place.
36. This is the amount of time it takes to take action on a soft sequence command. Vcc power must remain HIGH to effectively register command.
37. Commands such as STORE and RECALL lock out I/O until operation is complete which further increases this time. See the specific command.
Document #: 001-55720 Rev. *C
Page 22 of 27
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CY14B256KA
Truth Table For SRAM Operations
HSB must remain HIGH for SRAM operations.
Table 5. Truth Table
CE
H
L
WE
X
OE
X
Inputs/Outputs
Mode
Deselect/Power-down
Read
Power
High Z
Standby
H
L
Data out (DQ0–DQ7)
High Z
Active
Active
Active
L
H
H
Output disabled
Write
L
L
X
Data in (DQ0–DQ7)
Document #: 001-55720 Rev. *C
Page 23 of 27
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CY14B256KA
Ordering Information
Speed
(ns)
Package
Diagram
Operating
Range
Ordering Code
Package Type
25
CY14B256KA-SP25XIT
CY14B256KA-SP25XI
CY14B256KA-SP45XIT
CY14B256KA-SP45XI
51-85061
48-pin SSOP
Industrial
45
All the above parts are Pb-free.
Ordering Code Definition
CY 14 B 256 K A -SP 25 X I T
Option:
T - Tape and Reel
Blank - Std.
Temperature:
I - Industrial (–40 to 85 °C)
Pb-Free
Speed:
25 - 25 ns
45 - 45 ns
Package:
SP - 48 SSOP
Die revision:
Blank - No Rev
A - 1st Rev
Data Bus:
K - x8 + RTC
Density:
256 - 256 Kb
Voltage:
B - 3.0 V
14 - nvSRAM
Cypress
Document #: 001-55720 Rev. *C
Page 24 of 27
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CY14B256KA
Package Diagram
Figure 16. 48-Pin SSOP (51-85061)
51-85061 *D
Document #: 001-55720 Rev. *C
Page 25 of 27
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CY14B256KA
Acronyms
Document Conventions
Units of Measure
Acronym
BCD
Description
binary coded decimal
Symbol
Unit of Measure
nvSRAM
SSOP
RoHS
I/O
nonvolatile static random access memory
shrink small-outline package
restriction of hazardous substances
input/output
°C
degrees celsius
hertz
Hz
kbit
kHz
KΩ
μA
mA
μF
MHz
μs
1024 bits
kilohertz
CMOS
EIA
complementary metal oxide semiconductor
electronic industries alliance
Joint Electron Devices Engineering Council
read and write inhibited
kilo ohms
microamperes
milliampere
microfarads
megahertz
microseconds
millisecond
nanoseconds
picofarads
volts
JEDEC
RWI
RTC
real time clock
ms
ns
pF
V
Ω
ohms
W
watts
Document #: 001-55720 Rev. *C
Page 26 of 27
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CY14B256KA
Document History Page
Document Title: CY14B256KA 256-Kbit (32 K x 8) nvSRAM with Real Time Clock
Document Number: 001-55720
Orig. of Submission
Rev.
ECN No.
Description of Change
Change
GVCH
GVCH
Date
**
2763469
2829117
09/14/09 New Datasheet
*A
12/16/09 Added data retention and endurance table
Updated STORE cycles to QuantumTrap from 200K to 1 Million
Updated IBAK RTC backup current spec unit from nA to μA
Added Contents. Moved to external web
*B
*C
2922858
3143855
GVCH
GVCH
04/26/10 Pin Definitions: Added more clarity on HSB pin operation
Hardware STORE (HSB) Operation: Added more clarity on HSB pin operation
Updated HSB pin operation in Figure 11 and updated footnote 29
Updated package diagram.
01/17/2011 Updated Setting the Clock description
Added footnote 7
Updated ‘W’ bit description in Register Map Detail table
Updated Best Practices
Added tRTCp parameter to RTC Characteristics table
Figure 11: Typo error fixed
Added Acronyms table and Document Conventions table
Sales, Solutions, and Legal Information
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© Cypress Semiconductor Corporation, 2009-2011. The information contained herein is subject to change without notice. Cypress Semiconductor Corporation assumes no responsibility for the use of
any circuitry other than circuitry embodied in a Cypress product. Nor does it convey or imply any license under patent or other rights. Cypress products are not warranted nor intended to be used for
medical, life support, life saving, critical control or safety applications, unless pursuant to an express written agreement with Cypress. Furthermore, Cypress does not authorize its products for use as
critical components in life-support systems where a malfunction or failure may reasonably be expected to result in significant injury to the user. The inclusion of Cypress products in life-support systems
application implies that the manufacturer assumes all risk of such use and in doing so indemnifies Cypress against all charges.
Any Source Code (software and/or firmware) is owned by Cypress Semiconductor Corporation (Cypress) and is protected by and subject to worldwide patent protection (United States and foreign),
United States copyright laws and international treaty provisions. Cypress hereby grants to licensee a personal, non-exclusive, non-transferable license to copy, use, modify, create derivative works of,
and compile the Cypress Source Code and derivative works for the sole purpose of creating custom software and or firmware in support of licensee product to be used only in conjunction with a Cypress
integrated circuit as specified in the applicable agreement. Any reproduction, modification, translation, compilation, or representation of this Source Code except as specified above is prohibited without
the express written permission of Cypress.
Disclaimer: CYPRESS MAKES NO WARRANTY OF ANY KIND, EXPRESS OR IMPLIED, WITH REGARD TO THIS MATERIAL, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE. Cypress reserves the right to make changes without further notice to the materials described herein. Cypress does not
assume any liability arising out of the application or use of any product or circuit described herein. Cypress does not authorize its products for use as critical components in life-support systems where
a malfunction or failure may reasonably be expected to result in significant injury to the user. The inclusion of Cypress’ product in a life-support systems application implies that the manufacturer
assumes all risk of such use and in doing so indemnifies Cypress against all charges.
Use may be limited by and subject to the applicable Cypress software license agreement.
Document #: 001-55720 Rev. *C
Revised January 17, 2011
Page 27 of 27
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