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CY14B256KA
256 Kbit (32K x 8) nvSRAM with Real Time Clock
Features

256 Kbit nvSRAM 25 ns and 45 ns access times Internally organized as 32K x 8 (CY14B256KA) Hands off automatic STORE on power down with only a small capacitor STORE to QuantumTrap nonvolatile elements is initiated by software, hardware, or AutoStore on power down 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 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)
Industry Standard Configurations Single 3V +20%, -10% operation Industrial temperature 48-pin SSOP package Pb-free and RoHS compliance
Functional Description
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 incorporate 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. 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.
Logic Block Diagram
QuantumTrap 512 X 512
A5 A6 A7 A8 A9 A 11 A 12 A 13 A 14
V CC
V CAP V RTCbat V RTCcap
HSB
STORE
POWER CONTROL STORE/ RECALL CONTROL
ROW DECODER
STATIC RAM ARRAY 512 X 512
RECALL
SOFTWARE DETECT COLUMN IO
A14
- A0
DQ 0 DQ 2 DQ 3 DQ 4 DQ 5 DQ 6 DQ 7
INPUT BUFFERS
DQ 1
COLUMN DEC RTC
A 0 A 1 A 2 A 3 A 4 A 10
xout xin
INT
MUX
A14
- A0
OE
CE WE
Cypress Semiconductor Corporation Document #: 001-55720 Rev. *A
*
198 Champion Court
*
San Jose, CA 95134-1709 * 408-943-2600 Revised December 08, 2009
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Contents
Features ...............................................................................1 Functional Description .......................................................1 Contents ..............................................................................2 Pinouts ................................................................................3 Pin Definitions ....................................................................3 Device Operation ................................................................4 SRAM Read .........................................................................4 SRAM Write .........................................................................4 AutoStore Operation ..........................................................4 Hardware STORE (HSB) Operation ...................................5 Hardware RECALL (Power Up) ..........................................5 Software STORE .................................................................5 Software RECALL ...............................................................5 Preventing AutoStore .........................................................6 Best Practices .....................................................................7 Data Protection ...................................................................8 Noise Considerations .........................................................8 Real Time Clock Operation ................................................8 nvTIME Operation .........................................................8 Clock Operations ...........................................................8 Reading the Clock .........................................................8 Setting the Clock ...........................................................8 Backup Power ...............................................................8 Stopping and Starting the Oscillator ..............................9 Calibrating the Clock ..................................................... 9 Alarm ............................................................................. 9 Watchdog Timer ............................................................ 9 Power Monitor .............................................................10 Interrupts .....................................................................10 Flags Register .............................................................11 Maximum Ratings .............................................................16 Operating Range ...............................................................16 DC Electrical Characteristics ..........................................16 Capacitance ......................................................................17 Thermal Resistance ..........................................................17 AC Test Conditions ..........................................................17 RTC Characteristics .........................................................17 AC Switching Characteristics .........................................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 Package Diagram ..............................................................25 Document History Page ...................................................26 Sales, Solutions, and Legal Information ........................26 Worldwide Sales and Design Support .........................26 Products ......................................................................26
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Pinouts
Figure 1. Pin Diagram - 48-Pin SSOP
VCAP [1] NC A14 A12 A7 A6 A5 INT A4 NC NC NC VSS NC VRTCbat DQ0 A3 A2 A1 A0 DQ1 DQ2 Xout Xin 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 48 47 46 45 44 43 42 41 40 39 38 37 36 35 34 33 32 31 30 29 28 27 26 25 VCC NC[1] HSB WE A13 A8 A9 NC A11 NC NC NC VSS NC VRTCcap DQ6 OE A10 CE DQ7 DQ5 DQ4 DQ3 VCC
48 - SSOP
(x8)
Top View (not to scale)
Pin Definitions
Pin Name A0 - A14 DQ0 - DQ7 NC WE CE OE Xout Xin VRTCcap VRTCbat I/O Type Input Description Address Inputs Used to Select One of the 32,768 Bytes of the nvSRAM.
Input/Output Bidirectional Data I/O Lines. Used as input or output lines depending on operation. No Connect No Connects. This pin is not connected to the die. Input Input Input Output 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. Chip Enable Input, Active LOW. When LOW, selects the chip. When HIGH, deselects the chip. 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. Crystal Connection. Drives crystal on start up. Crystal Connection. For 32.768 kHz crystal.
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.
Notes 1. Address expansion for 1 Mbit. NC pin not connected to die.
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Pin Definitions (continued)
Pin Name INT VSS VCC HSB I/O Type Output Ground Description 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). Ground for the Device. Must be connected to the ground of the system.
Power Supply Power Supply Inputs to the Device. 3.0V +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. A weak internal pull up resistor keeps this pin HIGH if not connected (connection optional). After each STORE operation, HSB is driven HIGH for short time with standard output high current. Power Supply AutoStore Capacitor. Supplies power to the nvSRAM during power loss to store data from SRAM to nonvolatile elements.
VCAP
Device Operation
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.
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 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 may corrupt the data stored in nvSRAM. Figure 2. AutoStore Mode
VCC
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 tDOE, 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.
0.1uF 10kOhm VCC
SRAM Write
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.
WE
VCAP VCAP VSS
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 Page 4 of 26
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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. 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. The HSB signal is monitored by the system to detect if an AutoStore cycle is in progress.
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 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.
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 that is internally driven LOW to indicate a busy condition when the STORE (initiated by any means) is in progress. 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. 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 CY14B256KA remains disabled until the HSB pin returns HIGH. Leave the HSB unconnected if it is not used.
Software RECALL
Data is transferred from 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: 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 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.
Hardware RECALL (Power Up)
During power up or after any low power condition (VCC< VSWITCH), an internal RECALL request is latched. When 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.
Software STORE
Data is transferred from 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.
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Table 1. Mode Selection CE H L L L WE X H L H OE X L X L A14 - A0[2] X X X 0x0E38 0x31C7 0x03E0 0x3C1F 0x303F 0x0B45 0x0E38 0x31C7 0x03E0 0x3C1F 0x303F 0x0B46 0x0E38 0x31C7 0x03E0 0x3C1F 0x303F 0x0FC0 0x0E38 0x31C7 0x03E0 0x3C1F 0x303F 0x0C63 Mode Not Selected Read SRAM Write SRAM Read SRAM Read SRAM Read SRAM Read SRAM Read SRAM AutoStore Disable Read SRAM Read SRAM Read SRAM Read SRAM Read SRAM AutoStore Enable Read SRAM Read SRAM Read SRAM Read SRAM Read SRAM Nonvolatile STORE Read SRAM Read SRAM Read SRAM Read SRAM Read SRAM Nonvolatile Recall I/O Output High Z Output Data Input Data Output Data Output Data Output Data Output Data Output Data Output Data Output Data Output Data Output Data Output Data Output Data Output Data Output Data Output Data Output Data Output Data Output Data Output High Z Output Data Output Data Output Data Output Data Output Data Output High Z Power Standby Active Active Active[3]
L
H
L
Active[3]
L
H
L
Active ICC2[3]
L
H
L
Active[3]
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: 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 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.
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 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.
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.
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Best Practices
nvSRAM products have been used effectively for over 15 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:

or more random bytes) as part of the final system manufacturing test to ensure these system routines work consistently. 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. 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
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Data Protection
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.
Setting the Clock
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 nonvolatile 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. 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. Note The values entered in the timekeeping, alarm, calibration, and interrupt registers need a STORE operation to be saved in nonvolatile memory. Therefore, while working in AutoStore disabled mode, the user must perform a STORE operation after writing into the RTC registers for the RTC to work correctly.
Noise Considerations
Refer to CY application note AN1064.
Real Time Clock Operation
nvTIME Operation
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. 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 12 and Table 4 on page 13 for a detailed Register Map description.
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. 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. During backup operation, the CY14B256KA consumes 0.35 microamps (Typ) 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. Table 2. RTC Backup Time Capacitor Value 0.1F 0.47F 1.0F Backup Time 72 hours 14 days 30 days
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.
Reading the Clock
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. 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 3V 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.
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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. 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 OSCF (Oscillator Failed bit) 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 8), 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.
125,829,120 actual oscillator cycles, that is, 4.068 or -2.034 ppm of adjustment per calibration step in the Calibration register. 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. Note Setting or changing the Calibration register does not affect the test output frequency. To set or clear CAL, set the write bit "W" (in the flags register at 0x7FF0) to "1" to enable writes to the Flag 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 corresponding 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. 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. 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. Note CY14B256KA requires the alarm match bit for seconds (0x7FF2 - D7) to be set to `0' for proper operation of Alarm Flag and Interrupt.
Calibrating the Clock
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 25C. This implies an error of +2.5 seconds to -5 seconds per month. 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 corresponds to an adjustment of 4.068 or -2.034 ppm offset in oscillator error, depending on the sign. 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
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. Page 9 of 26
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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 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. 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. 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 registers.
.
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. 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. Interrupts are only generated while working on normal power and are not triggered when system is running in backup power mode.
Figure 3. Watchdog Timer Block Diagram
Oscillator
32,768 KHz
Clock Divider
32 Hz
1 Hz
Counter
Zero Compare
WDF
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.
Interrupt Register
WDS Load Register
D Q
WDW
Q
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. 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. 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. 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 10k resistor while using the interrupt in active LOW mode. 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 or Control register is read. When an enabled interrupt source activates the INT pin, an external host reads the Flags registers 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. Page 10 of 26
write to Watchdog Register
Watchdog 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 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. When operating from the backup source, read and write operations to nvSRAM are inhibited and the clock functions are not available to the user. The clock continues to operate in the background. The updated clock data is available to the user tHRECALL delay after VCC is restored to the device (see AutoStore/Power Up RECALL on page 20).
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Flags Register
The Flag 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 automat-
ically 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 9).
Figure 4. RTC Recommended Component Configuration
Recommended Values Y1 = 32.768 KHz (12.5 pF) C1 = 10 pF C2 = 67 pF
Note: The recommended values for C1 and C2 include board trace capacitance.
C1 C2
Y1
Xout Xin
Figure 5. Interrupt Block Diagram
WDF Watchdog Timer WIE PF Power Monitor VINT H/L AF Clock Alarm AIE PFE P/L Pin Driver
VCC
INT
VSS
WDF - Watchdog Timer Flag WIE - Watchdog Interrupt Enable PF - Power Fail Flag PFE - Power Fail Enable AF - Alarm Flag AIE - Alarm Interrupt Enable P/L - Pulse Level H/L - High/Low
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Table 3. RTC Register Map[4, 5] Register CY14B256KA 0x7FFF 0x7FFE 0x7FFD 0x7FFC 0x7FFB 0x7FFA 0x7FF9 0x7FF8 0 0 0 0 0 0 OSCEN (0) WDS (0) WIE (0) M (1) M (1) M (1) M (1) WDF 0 D7 D6 0 0 0 0 D5 0 10s Years 10s Months 0 0 BCD Format Data[4] D4 D3 D2 D1 Years Months Day Of Month Day of Week Hours Minutes Seconds Calibration (00000) D0 Function/Range Years: 00-99 Months: 01-12 Day of Month: 01-31 Day of Week: 01-07 Hours: 00-23 Minutes: 00-59 Seconds: 00-59 Calibration Values [6]
10s Day of Month 0 10s Minutes 10s Seconds Cal Sign (0) 10s Hours
0x7FF7 0x7FF6 0x7FF5 0x7FF4 0x7FF3 0x7FF2 0x7FF1 0x7FF0
WDW (0) AIE (0) 0 0 PFE (0) 0
WDT (000000) H/L (1) P/L (0) 0 0
Watchdog [6] Interrupts [6] Alarm, Day of Month: 01-31 Alarm, Hours: 00-23 Alarm, Minutes: 00-59 Alarm, Seconds: 00-59 Centuries: 00-99 R (0) Flags [6]
10s Alarm Date 10s Alarm Hours 10 Alarm Minutes 10 Alarm Seconds
Alarm Day Alarm Hours Alarm Minutes Alarm, Seconds Centuries 0 CAL (0) W (0)
10s Centuries AF PF OSCF
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.
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Table 4. Register Map Detail Register CY14B256KA 0x7FFF D7 D6 D5 10s Years Description Time Keeping - Years D4 D3 D2 Years D1 D0
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. 0x7FFE Time Keeping - Months D7 0 D6 0 D5 0 D4 10s Month D3 D2 Months D1 D0
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. 0x7FFD Time Keeping - Date D7 0 D6 0 D5 D4 D3 D2 D1 D0 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. 0x7FFC Time Keeping - Day D7 0 D6 0 D5 0 D4 0 D3 0 D2 D1 Day of Week D0
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. 0x7FFB Time Keeping - Hours D7 0 D6 0 D5 10s Hours D4 D3 D2 Hours D1 D0
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. 0x7FFA Time Keeping - Minutes D7 0 D6 D5 10s Minutes D4 D3 D2 Minutes D1 D0
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. 0x7FF9 Time Keeping - Seconds D7 0 D6 D5 10s Seconds D4 D3 D2 Seconds D1 D0
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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Table 4. Register Map Detail (continued) Register CY14B256KA 0x7FF8 D7 OSCEN OSCEN Calibration Sign Calibration 0x7FF7 D6 0 D5 Calibration Sign Description Calibration/Control D4 D3 D2 Calibration D1 D0
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. Determines if the calibration adjustment is applied as an addition (1) to or as a subtraction (0) from the time-base. These five bits control the calibration of the clock. WatchDog Timer D7 WDS D6 WDW D5 D4 D3 WDT D2 D1 D0
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. 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 9. Watchdog timeout selection. The watchdog timer interval is selected by the 6-bit value in this register. It represents 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 D7 WIE D6 AIE D5 PFE D4 0 D3 H/L D2 P/L D1 0 D0 0
WDW
WDT
0x7FF6
WIE AIE PFE 0 H/L P/L
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. 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. Reserved for future use 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 approximately 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 D7 M D6 0 D5 D4 D3 D2 D1 Alarm Date D0 10s Alarm Date
0x7FF5
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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Table 4. Register Map Detail (continued) Register CY14B256KA 0x7FF4 D7 M M D6 0 D5 Description Alarm - Hours D4 D3 D2 D1 D0 10s Alarm Hours Alarm Hours
Contains the alarm value for the hours and the mask bit to select or deselect the hours value. 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 D7 M M D6 D5 10s Alarm Minutes D4 D3 D2 D1 D0 Alarm Minutes
0x7FF3
Contains the alarm value for the minutes and the mask bit to select or deselect the minutes value. 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 D7 M M D6 D5 10s Alarm Seconds D4 D3 D2 D1 D0 Alarm Seconds
0x7FF2
Contains the alarm value for the seconds and the mask bit to select or deselect the seconds' value. 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 D7 D6 D5 D4 D3 D2 D1 Centuries D0 10s Centuries
0x7FF1
Contains the BCD value of centuries. 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 9. The range for the register is 0-99 centuries. 0x7FF0 Flags D7 WDF WDF AF PF OSCF D6 AF D5 PF D4 OSCF D3 0 D2 CAL D1 W D0 R
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. 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. 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 power cycle and is never cleared internally by the chip. The user must check for this condition and write '0' to clear this flag. 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 transfers the contents of the RTC registers to the time keeping counters if the time is changed (a new base time is loaded). This bit defaults to 0 on power up. 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.
CAL W
R
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Maximum Ratings
Exceeding maximum ratings may impair the useful life of the device. These user guidelines are not tested. Storage Temperature ................................. -65C to +150C Maximum Accumulated Storage Time At 150C Ambient Temperature........................ 1000h At 85C Ambient Temperature..................... 20 Years Ambient Temperature with Power Applied.. -55C to +150C Supply Voltage on VCC Relative to GND ..........-0.5V to 4.1V Voltage Applied to Outputs in High-Z State....................................... -0.5V to VCC + 0.5V Input Voltage.............................................-0.5V to Vcc+0.5V Transient Voltage (<20 ns) on Any Pin to Ground Potential .................. -2.0V to VCC + 2.0V Package Power Dissipation Capability (TA = 25C) ................................................... 1.0W Surface Mount Pb Soldering Temperature (3 Seconds) .......................................... +260C DC Output Current (1 output at a time, 1s duration).....15 mA Static Discharge Voltage.......................................... > 2001V (per MIL-STD-883, Method 3015) Latch Up Current .............................................. ..... > 200 mA
Operating Range
Range Industrial Ambient Temperature -40C to +85C VCC 2.7V to 3.6V
DC Electrical Characteristics
Over the Operating Range (VCC = 2.7V to 3.6V) Parameter VCC ICC1 Description Power Supply Voltage Average Vcc Current tRC = 25 ns tRC = 45 ns Values obtained without output loads (IOUT = 0 mA) Test Conditions Min 2.7 Typ[7] 3.0 Max 3.6 70 52 10 35 Unit V mA mA mA mA
ICC2 ICC3[7] ICC4
Average VCC Current All Inputs Don't Care, VCC = Max. during STORE Average current for duration tSTORE Average VCC Current All I/P cycling at CMOS levels. Values obtained without output loads (IOUT = 0 mA). at tRC= 200 ns, VCC (Typ), 25C Average VCAP Current during AutoStore Cycle All Inputs Don't Care. Average current for duration tSTORE
5
mA
ISB
VCC Standby Current CE > (VCC - 0.2V). VIN < 0.2V or > (VCC - 0.2V). W bit set to `0'. Standby current level after nonvolatile cycle is complete. Inputs are static. f = 0 MHz. Input Leakage VCC = Max, VSS < VIN < VCC Current (except HSB) Input Leakage Current (for HSB) VCC = Max, VSS < VIN < VCC VCC = Max, VSS < VOUT < VCC, CE or OE > VIH or WE < VIL -1 -100 -1 2.0 VSS - 0.5 2.4
5
mA
IIX[8]
+1 +1 +1 VCC + 0.5 0.8
A A A V V V
IOZ VIH VIL VOH VOL VCAP
Off State Output Leakage Current Input HIGH Voltage Input LOW Voltage
Output HIGH Voltage IOUT = -2 mA Output LOW Voltage IOUT = 4 mA Storage Capacitor Between VCAP pin and VSS, 5V Rated
0.4 61 68 180
V F
Notes 7. Typical values are at 25C, VCC= VCC (Typ). Not 100% tested. 8. The HSB pin has IOUT = -2 uA for VOH of 2.4V when both active HIGH and low drivers are disabled. When they are enabled standard VOH and VOL are valid. This parameter is characterized but not tested.
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Data Retention and Endurance
Parameter DATAR NVC Data Retention Nonvolatile STORE Operations Description Min 20 1,000 Unit Years K
Capacitance
Parameter[9] CIN COUT Description Input Capacitance Output Capacitance Test Conditions TA = 25C, f = 1 MHz, VCC = VCC (Typ) Max 7 7 Unit pF pF
Thermal Resistance
Parameter[9] Description Thermal Resistance (Junction to Ambient) Thermal Resistance (Junction to Case) Test Conditions Test conditions follow standard test methods and procedures for measuring thermal impedance, in accordance with EIA/JESD51. 48 SSOP 37.47 24.71 Unit C/W C/W
JA
JC
Figure 6. AC Test Loads
577 3.0V OUTPUT 30 pF R2 789 R1
577 3.0V OUTPUT 5 pF R2 789 R1
AC Test Conditions
Input Pulse Levels ....................................................0V to 3V Input Rise and Fall Times (10% - 90%) ........................ <3 ns Input and Output Timing Reference Levels .................... 1.5V
RTC Characteristics
Parameters VRTCbat IBAK[10] Description RTC Battery Pin Voltage RTC Backup Current Min 1.8 TA (Min) 25C TA (Max) TA (Min) 25C TA (Max) Typ[7] 3.0 0.35 1.6 1.5 1.4 350 0.5 3.6 3.6 3.6 2 850 Max 3.6 0.35 Units V A A A V V V sec
VRTCcap[11]
RTC Capacitor Pin Voltage
3.0 1
tOCS RBKCHG
RTC Oscillator Time to Start RTC Backup Capacitor Charge Current-Limiting Resistor
Notes 9. These parameters are guaranteed by design and are not tested. 10. From either VRTCcap or VRTCbat. 11. If VRTCcap > 0.5V or if no capacitor is connected to VRTCcap pin, the oscillator starts in tOCS time. If a backup capacitor is connected and VRTCcap < 0.5V, the capacitor must be allowed to charge to 0.5V for oscillator to start.
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AC Switching Characteristics
Parameters Cypress Alt Parameters Parameters SRAM Read Cycle tACS tACE [12] tRC tRC tAA [13] tDOE tOHA[13] tLZCE tHZCE tLZOE tPU
[9] [9] [9, 14] [9, 14] [9, 14]
25 ns Description Min Max 25 25 25 12 3 3 10 0 10 0 25 25 20 20 10 0 20 0 0 10 3 3 45 30 30 15 0 30 0 0 0 0 3 3 45
45 ns Min Max 45 45 20 Unit
Chip Enable Access Time Read Cycle Time Address Access Time 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 Write Cycle Time 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 Output Active after End of Write
ns ns ns ns ns ns
tAA tOE tOH tLZ tHZ tOLZ tOHZ tPA tPS tWC tWP tCW tDW tDH tAW tAS tWR tWZ tOW
15 15 45
ns ns ns ns ns ns ns ns ns ns ns ns ns ns ns
tHZOE [9, 14] tPD SRAM Write Cycle tWC tPWE tSCE tSD tHD tAW tSA tHA tHZWE [9, 14, 15] tLZWE
[9, 14]
15
Switching Waveforms
Figure 7. SRAM Read Cycle #1: Address Controlled [12, 13, 16]
tRC Address Address Valid tAA Data Output Previous Data Valid tOHA Output Data Valid
Notes 12. WE must be HIGH during SRAM read cycles. 13. Device is continuously selected with CE and OE LOW. 14. Measured 200 mV from steady state output voltage. 15. If WE is low when CE goes low, the outputs remain in the high impedance state. 16. HSB must remain HIGH during Read and Write cycles.
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Figure 8. SRAM Read Cycle #2: CE and OE Controlled [12, 16]
Address Address Valid tACE tAA tLZCE OE tLZOE Data Output High Impedance tPU Standby Active Output Data Valid tPD tDOE tHZOE tRC tHZCE
CE
ICC
Figure 9. SRAM Write Cycle #1: WE Controlled [15, 16, 17]
tWC Address Address Valid tSCE CE tAW tPWE WE tSA tSD Data Input tHZWE Data Output Previous Data tHD Input Data Valid tLZWE High Impedance tHA
Figure 10. SRAM Write Cycle #2: CE Controlled [15, 16, 17]
tWC Address tSA CE tPWE WE tSD Data Input Data Output
Note 17. CE or WE must be >VIH during address transitions.
Address Valid tSCE tHA
tHD
Input Data Valid High Impedance
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AutoStore/Power Up RECALL
Parameters tHRECALL tDELAY
[18]
Description Power Up RECALL Duration STORE Cycle Duration Time Allowed to Complete SRAM Write Cycle Low Voltage Trigger Level VCC Rise Time HSB Output Disable Voltage HSB To Output Active Time HSB High Active Time
Min
Max 20 8 25 2.65
Unit ms ms ns V s V s ns
tSTORE [19]
[20]
VSWITCH tVCCRISE VHDIS[9] tLZHSB[9] tHHHD[9]
[9]
150 1.9 5 500
Switching Waveforms
Figure 11. AutoStore or Power Up RECALL [21]
VCC VSWITCH VHDIS
VVCCRISE tHHHD HSB OUT tLZHSB
Note19
tSTORE tHHHD tDELAY tLZHSB
Note19
tSTORE Note
22
AutoStore POWERUP RECALL Read & Write Inhibited (RWI)
tDELAY
tHRECALL
tHRECALL
POWER-UP RECALL
Read & Write
BROWN OUT AutoStore
POWER-UP RECALL
Read & Write
POWER DOWN AutoStore
Notes 18. tHRECALL starts from the time VCC rises above VSWITCH. 19. If an SRAM write has not taken place since the last nonvolatile cycle, no AutoStore or Hardware STORE takes place 20. On a Hardware Store and AutoStore initiation, SRAM write operation continues to be enabled for time tDELAY. 21. Read and Write cycles are ignored during STORE, RECALL, and while VCC is below VSWITCH. 22. HSB pin is driven HIGH to VCC only by internal 100 k resistor, HSB driver is disabled.
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Software Controlled STORE/RECALL Cycle
Parameters[23, 24] tRC tSA tCW tHA tRECALL tSS [25, 26] Description STORE/RECALL Initiation Cycle Time Address Setup Time Clock Pulse Width Address Hold Time RECALL Duration Soft Sequence Processing Time 25 ns Min 25 0 20 0 Max Min 45 0 30 0 45 ns Max Unit ns ns ns ns s s
200 100
200 100
Switching Waveforms
Figure 12. CE & OE Controlled Software STORE/RECALL Cycle [24]
tRC Address tSA CE tSA OE tHHHD HSB (STORE only) DQ (DATA) tLZCE tHZCE t DELAY Note
27
tRC Address #6 tCW tHA tHA
Address #1 tCW
tHA
tHA
High Impedance tSTORE/tRECALL
tLZHSB
RWI
Figure 13. AutoStore Enable/Disable Cycle
tRC Address tSA CE tSA OE tLZCE DQ (DATA) tHZCE tSS Note
27
tRC Address #6 tCW
Address #1 tCW tHA tHA
tHA
tHA
t DELAY
Notes 23. The software sequence is clocked with CE controlled or OE controlled reads. 24. The six consecutive addresses must be read in the order listed in Table 1. WE must be HIGH during all six consecutive cycles. 25. 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. 26. Commands such as STORE and RECALL lock out I/O until operation is complete which further increases this time. See the specific command. 27. DQ output data at the sixth read may be invalid since the output is disabled at tDELAY time.
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Hardware STORE Cycle
Parameters tDHSB tPHSB Description HSB To Output Active Time when write latch not set Hardware STORE Pulse Width 15 Min Max 25 Unit ns ns
Switching Waveforms
Figure 14. Hardware STORE Cycle[19]
Write latch set
tPHSB HSB (IN) tDELAY HSB (OUT) DQ (Data Out) RWI tLZHSB tSTORE tHHHD
Write latch not set
tPHSB HSB (IN) HSB pin is driven high to VCC only by Internal 100kOhm resistor, 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[25, 26]
Soft Sequence Command Address Address #1 tSA Address #6 tCW tSS Soft Sequence Command Address #1 Address #6 tCW tSS
CE VCC
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Truth Table For SRAM Operations
HSB must remain HIGH for SRAM operations. Table 5. Truth Table CE H L L L WE X H H L OE X L H X High Z Data Out (DQ0-DQ7) High Z Data in (DQ0-DQ7) Inputs/Outputs Read Output Disabled Write Mode Deselect/Power Down Standby Active Active Active Power
Part Numbering Nomenclature CY 14 B 256 K A -SP 25 X I T
Option: T - Tape and Reel Blank - Std. Temperature: I - Industrial (-40 to 85C) 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 - 3.0V 14 - nvSRAM
Cypress
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Ordering Information
Speed (ns) 25 45 Ordering Code CY14B256KA-SP25XIT CY14B256KA-SP25XI CY14B256KA-SP45XIT CY14B256KA-SP45XI
All the above parts are Pb-free.
Package Diagram 51-85061 48-pin SSOP
Package Type
Operating Range Industrial
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CY14B256KA
Package Diagram
Figure 16. 48-Pin SSOP (51-85061)
51-85061 *C
Document #: 001-55720 Rev. *A
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CY14B256KA
Document History Page
Document Title: CY14B256KA 256 Kbit (32K x 8) nvSRAM with Real Time Clock Document Number: 001-55720 Orig. of Submission Revision ECN Description of Change Change Date ** 2763469 GVCH 09/14/09 New Datasheet *A 2829117 GVCH 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 A Added Contents. Moved to external web
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(c) Cypress Semiconductor Corporation, 2008-2009. 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. *A
Revised December 08, 2009
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All products and company names mentioned in this document are the trademarks of their respective holders.
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