CY14B256P_1106

CY14B256P 256-Kbit (32 K × 8) Serial (SPI) nvSRAM with Real Time Clock Features ■ ■ 256-Kbit nonvolatile static random access memory (nvSRAM) ❐ Internally organized as 32 K × 8 ❐ STORE to QuantumTrap nonvolatile elements initiated automatically on power-down (AutoStore) or by user using HSB pin (Hardware STORE) or SPI instruction (Software STORE) ❐ RECALL to SRAM initiated on power-up (Power-Up RECALL) or by SPI instruction (Software RECALL) ❐ Automatic STORE on power-down with a small capacitor High reliability ❐ ❐ ❐ Write protection ❐ Hardware protection using Write Protect (WP) pin ❐ Software protection using Write Disable instruction ❐ Software block protection for 1/4, 1/2, or entire array Low power consumption ❐ Single 3 V +20%, –10% operation ❐ Average active current of 10 mA at 40 MHz operation Industry standard configurations ❐ Industrial temperature ❐ 16-pin small outline integrated circuit (SOIC) package ❐ Restriction of hazardous substances (RoHS) compliant ■ ■ ■ Infinite read, write, and RECALL cycles 1 million STORE cycles to QuantumTrap Data retention: 20 years Overview The Cypress CY14B256P combines a 256-Kbit nvSRAM[1] with a full-featured real time clock in a monolithic integrated circuit with serial SPI interface. The memory is organized as 32 K words of 8 bits each. The embedded nonvolatile elements incorporate the QuantumTrap technology, creating the world’s most reliable nonvolatile memory. The SRAM provides infinite read and write cycles, while the QuantumTrap cells provide highly reliable nonvolatile storage of data. Data transfers from SRAM to the nonvolatile elements (STORE operation) takes place automatically at power-down. On power-up, data is restored to the SRAM from the nonvolatile memory (RECALL operation). The STORE and RECALL operations can also be initiated by the user through SPI instruction. ■ Real time clock (RTC) ❐ Full-featured RTC ❐ Watchdog timer ❐ Clock alarm with programmable interrupts ❐ Capacitor or battery backup for RTC ❐ Backup current of 0.35 µA (typical) High-speed serial peripheral interface (SPI) ❐ 40-MHz clock rate – SRAM memory access ❐ 25-MHz clock rate – RTC memory access ❐ Supports SPI mode 0 (0,0) and mode 3 (1,1) ■ Logic Block Diagram VCC VCAP CS WP SCK HOLD Instruction decode Write protect Control logic QuantumTrap 32 K X 8 Power Control SRAM Array 32 K X 8 STORE RECALL STORE/RECALL Control HSB Instruction register A0-A14 Address Decoder D0-D7 RTC Xout X in INT MUX SI Data I/O register SO Status Register Note 1. This device will be referred to as nvSRAM throughout the document. Cypress Semiconductor Corporation Document Number: 001-53881 Rev. *F • 198 Champion Court • San Jose, CA 95134-1709 • 408-943-2600 Revised July 19, 2011 For Evaluation Samples only. Production will be supported with the next revision silicon in SOIC package. 256-Kbit (32 K × 8) Serial (SPI) nvSRAM with Real Time Clock CY14B256P Contents Pinouts .............................................................................. 3 Device Operation .............................................................. 4 SRAM Write.................................................................. 4 SRAM Read ................................................................ 4 STORE Operation ....................................................... 4 AutoStore Operation .................................................... 4 Software STORE Operation ........................................ 5 Hardware STORE and HSB Pin Operation ................. 5 RECALL Operation...................................................... 5 Hardware RECALL (Power-Up) .................................. 5 Software RECALL ....................................................... 5 Disabling and Enabling AutoStore............................... 5 Noise Considerations....................................................... 5 Serial Peripheral Interface ............................................... 6 SPI Overview ............................................................... 6 SPI Modes ......................................................................... 7 SPI Operating Features..................................................... 8 Power-Up .................................................................... 8 Power On Reset .......................................................... 8 Power-Down ................................................................ 8 Active Power and Stand ................... by Power Modes 8 SPI Functional Description.............................................. 8 Status Register ................................................................. 9 Read Status Register (RDSR) Instruction ................... 9 Write Status Register (WRSR) Instruction .................. 9 Write Protection and Block Protection ......................... 10 Write Enable (WREN) Instruction .............................. 10 Write Disable (WRDI) Instruction .............................. 10 Block Protection ........................................................ 10 Hardware Write Protection (WP Pin)......................... 11 Memory Access .............................................................. 11 Read Sequence (READ) instruction .......................... 11 Write Sequence (WRITE) instruction ........................ 11 RTC Access ..................................................................... 13 READ RTC (RDRTC) Instruction .............................. 13 WRITE RTC (WRTC) Instruction ............................... 13 Software STORE (STORE) instruction ...................... 14 Software RECALL (RECALL) instruction .................. 14 AutoStore Enable (ASENB) instruction ..................... 14 AutoStore Disable (ASDISB) instruction ................... 15 HOLD Pin Operation ................................................. 15 Real Time Clock Operation............................................. 16 nvTime Operation...................................................... 16 Clock Operations ....................................................... 16 Reading the Clock ..................................................... 16 Setting the Clock ....................................................... 16 Backup Power ........................................................... 16 Stopping and Starting the Oscillator .......................... 16 Calibrating the Clock ................................................. 17 Alarm ......................................................................... 17 Watchdog Timer ........................................................ 17 Power Monitor ........................................................... 18 Interrupts ................................................................... 18 Flags Register ........................................................... 18 Accessing the Real Time Clock through SPI............. 19 Best Practices................................................................. 24 Maximum Ratings ........................................................... 25 DC Electrical Characteristics ........................................ 25 Data Retention and Endurance ..................................... 26 Capacitance .................................................................... 26 Thermal Resistance........................................................ 26 AC Test Conditions ........................................................ 26 RTC Characteristics ....................................................... 27 AC Switching Characteristics ....................................... 27 AutoStore or Power-Up RECALL .................................. 29 Software Controlled STORE/RECALL Cycles .............. 30 Hardware STORE Cycle ................................................. 31 Ordering Information ...................................................... 32 Ordering Code Definition........................................... 32 Package Diagram ............................................................ 33 Acronyms ........................................................................ 34 Document Conventions ................................................. 34 Units of Measure ....................................................... 34 Document History Page ................................................. 35 Sales, Solutions, and Legal Information ...................... 36 Worldwide Sales and Design Support....................... 36 Products .................................................................... 36 PSoC Solutions ......................................................... 36 Document Number: 001-53881 Rev. *F Page 2 of 36 For Evaluation Samples only. Production will be supported with the next revision silicon in SOIC package. CY14B256P Pinouts For Evaluation Samples only. Production will be supported with the next revision silicon in SOIC package. Figure 1. Pin Diagram – 16-pin SOIC VCC INT VCAP SO SI SCK CS HSB NC VRTCbat Xout Xin WP HOLD VRTCcap VSS 1 2 3 4 5 6 7 8 Top View not to scale 16 15 14 13 12 11 10 9 Table 1. Pin Definitions Pin Name CS SCK SI SO WP HOLD HSB I/O Type Input Input Input Output Input Input Input/output Description Chip select. Activates the device when pulled LOW. Driving this pin HIGH puts the device in low power standby mode. Serial clock. Runs at speeds up to maximum of fSCK. Serial input is latched at the rising edge of this clock. Serial output is driven at the falling edge of the clock. Serial input. Pin for input of all SPI instructions and data. Serial output. Pin for output of data through SPI. Write protect. Implements hardware write protection in SPI. HOLD pin. Suspends serial operation. Hardware STORE busy: Output: Indicates busy status of nvSRAM when LOW. 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). Input: Hardware STORE implemented by pulling this pin LOW externally. AutoStore capacitor. Supplies power to the nvSRAM during power loss to STORE data from the SRAM to nonvolatile elements. If AutoStore is not needed, this pin must be left as No Connect. It must never be connected to ground. Capacitor backup for RTC. Left unconnected if VRTCbat is used. Battery backup for RTC. Left unconnected if VRTCcap is used. Crystal output connection. Drives crystal on start up. Crystal input connection. For 32.768 kHz crystal. 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). No connect. This pin is not connected to the die. Ground Power supply (2.7 V to 3.6 V) VCAP VRTCcap VRTCbat Xout Xin INT NC VSS VCC Power supply Power supply Power supply Output Input Output No connect Power supply Power supply Document Number: 001-53881 Rev. *F Page 3 of 36 CY14B256P Device Operation CY14B256P is a 256-Kbit nvSRAM memory with integrated RTC and SPI interface. All the reads and writes to nvSRAM happen to the SRAM which gives nvSRAM the unique capability to handle infinite writes to the memory. The data in SRAM is secured by a STORE sequence that transfers the data in parallel to the nonvolatile QuantumTrap cells. A small capacitor (VCAP) is used to AutoStore the SRAM data in nonvolatile cells when power goes down providing power-down data security. The QuantumTrap nonvolatile elements built in the reliable SONOS technology make nvSRAM the ideal choice for secure data storage. In CY14B256P, the 256-Kbit memory array is organized as 32 K words × 8 bits. The memory is accessed through a standard SPI interface that enables very high clock speeds up to 40 MHz with zero cycle delay read and write cycles. CY14B256P supports SPI modes 0 and 3 (CPOL, CPHA = 0, 0 and 1, 1) and operates as SPI slave. The device is enabled using the chip select (CS) pin and accessed through serial input (SI), serial output (SO), and serial clock (SCK) pins. CY14B256P provides the feature for hardware and software write protection through the WP pin and WRDI instruction. CY14B256P also provides mechanisms for block write protection (quarter, half, or full array) using BP0 and BP1 pins in the Status Register. Further, the HOLD pin is used to suspend any serial communication without resetting the serial sequence. CY14B256P uses the standard SPI opcodes for memory access. In addition to the general SPI instructions for read and write, CY14B256P provides four special instructions that allow access to four nvSRAM specific functions: STORE, RECALL, AutoStore Disable (ASDISB), and AutoStore Enable (ASENB). The major benefit of nvSRAM over serial EEPROMs is that all reads and writes to nvSRAM are performed at the speed of SPI bus with zero cycle delay. Therefore, no wait time is required after any of the memory accesses. The STORE and RECALL operations need finite time to complete and all memory accesses are inhibited during this time. While a STORE or RECALL operation is in progress, the busy status of the device is indicated by the Hardware STORE Busy (HSB) pin and also reflected on the RDY bit of the Status Register. SRAM Read STORE Operation STORE operation transfers the data from the SRAM to the nonvolatile QuantumTrap cells. The CY14B256P STOREs data to the nonvolatile cells using one of the three STORE operations: AutoStore, activated on device power-down; Software STORE, activated by a STORE instruction; and Hardware STORE, activated by the HSB. 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, read/write to CY14B256P is inhibited until the cycle is completed. The HSB signal or the RDY bit in the Status Register can be monitored by the system to detect if a STORE or Software RECALL cycle is in progress. The busy status of nvSRAM is indicated by HSB being pulled LOW or RDY bit being set to ‘1’. To avoid 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. However, software initiated STORE cycles are performed regardless of whether a write operation has taken place. AutoStore Operation The AutoStore operation is a unique feature of nvSRAM which automatically stores the SRAM data to QuantumTrap cells during power-down. This STORE makes use of an external capacitor (VCAP) and enables the device to safely STORE the data in the nonvolatile memory when power goes down. During normal operation, the device draws current from VCC to charge the capacitor connected to the VCAP pin. When the voltage on the VCC pin drops below VSWITCH during power-down, the device inhibits all memory accesses to nvSRAM and automatically performs a conditional STORE operation using the charge from the VCAP capacitor. The AutoStore operation is not initiated if no write cycle was performed since the last RECALL. Note If a capacitor is not connected to VCAP pin, AutoStore must be disabled by issuing the AutoStore Disable instruction specified in AutoStore Enable (ASENB) instruction on page 14. If 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 the nvSRAM and Status Register. To resume normal functionality, the WRSR instruction must be issued to update the nonvolatile bits BP0, BP1 and WPEN in the Status Register. SRAM Write All writes to nvSRAM are carried out on the SRAM and do not use up any endurance cycles of the nonvolatile memory. This enables the user to perform infinite write operations. A write cycle is performed through the WRITE instruction. The WRITE instruction is issued through the SI pin of the nvSRAM and consists of the WRITE opcode, two bytes of address, and one byte of data. Write to nvSRAM is done at SPI bus speed with zero cycle delay. CY14B256P allows burst mode writes to be performed through SPI. This enables write operations on consecutive addresses without issuing a new WRITE instruction. When the last address in memory is reached in burst mode, the address rolls over to 0x0000 and the device continues to write. The SPI write cycle sequence is defined in the Memory Access section of SPI Protocol Description. Document Number: 001-53881 Rev. *F Page 4 of 36 For Evaluation Samples only. Production will be supported with the next revision silicon in SOIC package. A read cycle in CY14B256P is performed at the SPI bus speed and the data is read out with zero cycle delay after the READ instruction is executed. The READ instruction is issued through the SI pin of the nvSRAM and consists of the READ opcode and two bytes of address. The data is read out on the SO pin. CY14B256P allows burst mode reads to be performed through SPI. This enables reads on consecutive addresses without issuing a new READ instruction. When the last address in memory is reached in burst mode read, the address rolls over to 0x0000 and the device continues to read. The SPI read cycle sequence is defined in the Memory Access section of SPI Protocol Description. CY14B256P Figure 2 shows the proper connection of the storage capacitor (VCAP) for AutoStore operation. Refer to DC Electrical Characteristics on page 25 for the size of the VCAP. Figure 2. AutoStore Mode VCC RECALL Operation A RECALL operation transfers the data stored in the nonvolatile QuantumTrap elements to the SRAM. In CY14B256P, a RECALL may be initiated in two ways: Hardware RECALL, initiated on power-up; and Software RECALL, initiated by a SPI RECALL instruction. Internally, RECALL is a two step procedure. First, the SRAM data is cleared. Next, the nonvolatile information is transferred into the SRAM cells. All memory accesses are inhibited while a RECALL cycle is in progress. The RECALL operation does not alter the data in the nonvolatile elements. 0.1 uF 10 kOhm VCC CS VCAP VCAP Hardware RECALL (Power-Up) VSS During power-up, when VCC crosses VSWITCH, an automatic RECALL sequence is initiated, which transfers the content of nonvolatile memory on to the SRAM. A Power-Up RECALL cycle takes tFA time to complete and the memory access is disabled during this time. HSB pin is used to detect the Ready status of the device. Software STORE Operation Software STORE allows the user to trigger a STORE operation through a special SPI instruction. STORE operation is initiated by executing STORE instruction irrespective of whether a write has been performed since the last NV operation. A STORE cycle takes tSTORE time to complete, during which all the memory accesses to nvSRAM are inhibited. The RDY bit of the Status Register or the HSB pin may be polled to find the Ready/Busy status of the nvSRAM. After the tSTORE cycle time is completed, the SRAM is activated again for read and write operations. Software RECALL Software RECALL allows the user to initiate a RECALL operation to restore the content of nonvolatile memory on to the SRAM. In CY14B256P, this can be done by issuing a RECALL instruction in SPI. A Software RECALL takes tRECALL time to complete during which all memory accesses to nvSRAM are inhibited. The controller must provide sufficient delay for the RECALL operation to complete before issuing any memory access instructions. Disabling and Enabling AutoStore If the application does not require the AutoStore feature, it can be disabled in CY14B256P by using the ASDISB instruction. If this is done, the nvSRAM does not perform a STORE operation at power-down. Note CY14B256P comes from the factory with AutoStore Enabled. AutoStore can be re-enabled by using the ASENB instruction. However, these operations are not nonvolatile and if the user needs this setting to survive the power cycle, a STORE operation must be performed following AutoStore Disable or Enable operation. Note If AutoStore is disabled and VCAP is not required, then the VCAP pin must be left open. The VCAP pin must never be connected to ground. The power-up RECALL operation cannot be disabled in any case. Hardware STORE and HSB Pin Operation The HSB pin in CY14B256P is used to control and acknowledge STORE operations. If no STORE/RECALL is in progress, this pin can be used to request a Hardware STORE cycle. When the HSB pin is driven LOW, the CY14B256P conditionally initiates a STORE operation after tDELAY duration. An actual STORE cycle starts only if a write to the SRAM is performed since the last STORE or RECALL cycle. Reads and writes to the memory are inhibited for tSTORE duration or as long as HSB pin is LOW. 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. 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 an internal 100 kΩ pull-up resistor. Note For successful last data byte STORE, a hardware store should be initiated atleast one clock cycle after the last data bit D0 is received. Noise Considerations Refer to CY application note AN1064. Document Number: 001-53881 Rev. *F Page 5 of 36 For Evaluation Samples only. Production will be supported with the next revision silicon in SOIC package. Upon completion of the STORE operation, the nvSRAM memory access is inhibited for tLZHSB time after HSB pin returns HIGH. The HSB pin must be left unconnected if not used. CY14B256P Serial Peripheral Interface SPI Overview The SPI is a four-pin interface with chip select (CS), serial input (SI), serial output (SO), and serial clock (SCK) pins. CY14B256P provides serial access to nvSRAM through SPI interface. The SPI bus on CY14B256P can run at speeds of up to 40 MHz for all instructions except RDRTC which runs at 25 MHz. The SPI is a synchronous serial interface which uses clock and data pins for memory access and supports multiple devices on the data bus. A device on SPI bus is activated using the CS pin. The relationship between chip select, clock, and data is dictated by the SPI mode. CY14B256P supports SPI modes 0 and 3. In both these modes, data is clocked into the nvSRAM on the rising edge of SCK starting from the first rising edge after CS goes active. The SPI protocol is controlled by opcodes. These opcodes specify the commands from the bus master to the slave device. After CS is activated the first byte transferred from the bus master is the opcode. Following the opcode, any addresses and data are then transferred. The CS must go inactive after an operation is complete and before a new opcode can be issued. The commonly used terms used in SPI protocol are as follows. SPI Master The SPI master device controls the operations on a SPI bus. A SPI bus may have only one master with one or more slave devices. All the slaves share the same SPI bus lines and the master may select any of the slave devices using the CS pin. All the operations must be initiated by the master activating a slave device by pulling the CS pin of the slave LOW. The master also generates the SCK and all the data transmission on SI and SO lines are synchronized with this clock. SPI Slave The SPI slave device is activated by the master through the chip select line. A slave device gets the SCK as an input from the SPI master and all the communication is synchronized with this clock. SPI slave never initiates a communication on the SPI bus and acts on the instruction from the master. CY14B256P operates as a slave device and may share the SPI bus with multiple CY14B256P devices or other SPI devices. Chip Select (CS) For selecting any slave device, the master needs to pull-down the corresponding CS pin. Any instruction can be issued to a slave device only when the CS pin is LOW. The CY14B256P is selected when the CS pin is LOW. When the device is not selected, data through the SI pin is ignored and the serial output pin (SO) remains in a high-impedance state. Note A new instruction must begin with the falling edge of CS. Therefore, only one opcode can be issued for each active chip select cycle. Serial Clock (SCK) CY14B256P allows SPI modes 0 and 3 for data communication. In both these modes, the inputs are latched by the slave device on the rising edge of SCK and outputs are issued on the falling edge. Therefore, the first rising edge of SCK signifies the arrival of the first bit (MSB) of SPI instruction on the SI pin. Further, all data inputs and outputs are synchronized with SCK. Data Transmission SI and SO SPI data bus consists of two lines, SI and SO, for serial data communication. The SI is also referred to as Master Out Slave In (MOSI) and SO is referred to as Master In Slave Out (MISO). The master issues instructions to the slave through the SI pin, while the slave responds through the SO pin. Multiple slave devices may share the SI and SO lines as described earlier. CY14B256P has two separate pins for SI and SO which can be connected with the master as shown in Figure 3 on page 7. Most Significant Bit (MSB) The SPI protocol requires that the first bit to be transmitted is the most significant bit (MSB). This is valid for both address and data transmission. The 256-Kbit serial nvSRAM requires a 2-byte address for any read or write operation. However, because the address is only 15 bits, it implies that the first MSB which is fed in is ignored by the device. Although this bit is ‘don’t care’, Cypress recommends that this bit is treated as 0 to enable seamless transition to higher memory densities. Serial Opcode After the slave device is selected with CS going LOW, the first byte received is treated as the opcode for the intended operation. CY14B256P uses the standard opcodes for memory accesses. In addition to the memory accesses, CY14B256P provides additional opcodes for the nvSRAM specific functions: STORE, RECALL, AutoStore Enable, and AutoStore Disable. Refer to Table 2 on page 8 for details on opcodes. Invalid Opcode If an invalid opcode is received, the opcode is ignored and the device ignores any additional serial data on the SI pin till the next falling edge of CS and the SO pin remains tri-stated. Status Register CY14B256P has an 8-bit Status Register. The bits in the Status Register are used to configure the SPI bus. These bits are described in the Table 4 on page 9. Document Number: 001-53881 Rev. *F Page 6 of 36 For Evaluation Samples only. Production will be supported with the next revision silicon in SOIC package. Serial clock is generated by the SPI master and the communication is synchronized with this clock after CS goes LOW. CY14B256P SCK M OSI M IS O SCK SI SO SCK SI SO u C o n tro lle r C Y14B 256P C Y14B 256P CS HO LD CS HO LD CS1 HO LD 1 CS2 HO LD 2 SPI Modes CY14B256P device may be driven by a microcontroller with its SPI peripheral running in either of these two modes: ■ ■ The two SPI modes are shown in Figure 4 and Figure 5. The status of clock when the bus master is in standby mode and not transferring data is: ■ SPI Mode 0 (CPOL=0, CPHA=0) SPI Mode 3 (CPOL=1, CPHA=1) SCK remains at 0 for Mode 0 For both these modes, the input data is latched in on the rising edge of SCK starting from the first rising edge after CS goes active. If the clock starts from a HIGH state (in mode 3), the first rising edge after the clock toggles is considered. The output data is available on the falling edge of SCK. Figure 4. SPI Mode 0 CS ■ SCK remains at 1 for Mode 3 CPOL and CPHA bits must be set in the SPI controller for the either Mode 0 or Mode 3. CY14B256P detects the SPI mode from the status of SCK pin when the device is selected by bringing the CS pin LOW. If SCK pin is LOW when the device is selected, SPI Mode 0 is assumed and if SCK pin is HIGH, CY14B256P works in SPI Mode 3. Figure 5. SPI Mode 3 CS 0 SCK 1 2 3 4 5 6 7 SCK 0 1 2 3 4 5 6 7 SI 7 MSB 6 5 4 3 2 1 0 LSB SI 7 MSB 6 5 4 3 2 1 0 LSB Document Number: 001-53881 Rev. *F Page 7 of 36 For Evaluation Samples only. Production will be supported with the next revision silicon in SOIC package. Figure 3. System Configuration using SPI nvSRAM CY14B256P SPI Operating Features Power-Up Power-up is defined as the condition when the power supply is turned on and VCC crosses Vswitch voltage. During this time, the CS must be enabled to follow the VCC voltage. Therefore, CS must be connected to VCC through a suitable pull-up resistor. As a built in safety feature, CS is both edge-sensitive and level-sensitive. After power-up, the device is not selected until a falling edge is detected on CS. This ensures that CS must have been HIGH, before going LOW to start the first operation. As described earlier, nvSRAM performs a Power-Up RECALL operation after power-up and therefore, all memory accesses are disabled for tFA duration after power-up. The HSB pin can be probed to check the Ready/Busy status of nvSRAM after power-up. Active Power and Standby Power Modes SPI Functional Description The CY14B256P uses an 8-bit instruction register. Instructions and their operation codes are listed in Table 2. All instructions, addresses, and data are transferred with the MSB first and start with a HIGH to LOW CS transition. There are, in all, 12 SPI instructions that provide access to most of the functions in nvSRAM. Further, the WP, HOLD and HSB pins provide additional functionality driven through hardware. Table 2. Instruction Set Instruction Category Instruction Name WREN Status Register instructions WRDI RDSR WRSR SRAM read/write instructions RTC read/write instructions READ WRITE RDRTC WRTC STORE Special NV instructions RECALL ASENB ASDISB Reserved - Reserved Opcode 0000 0110 0000 0100 0000 0101 0000 0001 0000 0011 0000 0010 0001 0011 0001 0010 0011 1100 0110 0000 0101 1001 0001 1001 0001 1110 Operation Set write enable latch Reset write enable latch Read Status Register Write Status Register Read data from memory array Write data to memory array Read RTC registers Write RTC registers Software STORE Software RECALL AutoStore enable AutoStore disable Power On Reset A power on reset (POR) circuit is included to prevent inadvertent writes. At power-up, the device does not respond to any instruction until the VCC reaches the POR threshold voltage (VSWITCH). After VCC transitions the POR threshold, the device is internally reset and performs an Power-Up RECALL operation. During Power-Up RECALL all device accesses are inhibited. The device is in the following state after POR: ■ ■ ■ ■ Deselected (after power-up, a falling edge is required on CS before any instructions are started). Standby power mode Not in the HOLD condition Status Register state: ❐ Write enable (WEN) bit is reset to ‘0’. ❐ WPEN, BP1, BP0 unchanged from previous STORE operation ❐ Don’t care bits 4-6 are reset to ‘0’. The WPEN, BP1, and BP0 bits of the Status Register are nonvolatile bits and remain unchanged from the previous STORE operation. Prior to selecting and issuing instructions to the memory, a valid and stable VCC voltage must be applied. This voltage must remain valid until the end of the instruction transmission. Power-Down At power-down (continuous decay of VCC), when VCC drops from the normal operating voltage and below the VSWITCH threshold voltage, the device stops responding to any instruction sent to it. If a write cycle is in progress and the last data bit D0 has been received when the power goes down, it is allowed tDELAY time to complete the write. After this, all memory accesses are inhibited and a conditional AutoStore operation is performed (AutoStore is not performed if no writes have happened since the last RECALL cycle). This feature prevents inadvertent writes to nvSRAM from happening during power-down. However, to avoid the possibility of inadvertent writes during power-down, ensure that the device is deselected and is in standby power mode, and the CS follows the voltage applied on VCC. The SPI instructions in CY14B256P are divided based on their functionality in the following types: ❐ Status Register access: RDSR and WRSR instructions ❐ Write protection functions: WREN and WRDI instructions along with WP pin and WEN, BP0, and BP1 bits ❐ SRAM memory access: READ and WRITE instructions ❐ RTC access: RDRTC and WRTC instructions ❐ nvSRAM special instructions: STORE, RECALL, ASENB, and ASDISB Page 8 of 36 Document Number: 001-53881 Rev. *F For Evaluation Samples only. Production will be supported with the next revision silicon in SOIC package. When CS is LOW, the device is selected and is in the active power mode. The device consumes ICC current, as specified in DC Electrical Characteristics on page 25. When CS is HIGH, the device is deselected and the device goes into the standby power mode if a STORE or RECALL cycle is not in progress. If a STORE/RECALL cycle is in progress, the device goes into the standby power mode after the STORE/RECALL cycle is completed. In the standby power mode, the current drawn by the device drops to ISB. CY14B256P Status Register The Status Register bits are listed in Table 3. The Status Register consists of a Ready bit (RDY) and data protection bits BP1, BP0, WEN, and WPEN. The RDY bit can be polled to check the ready/busy status while a nvSRAM STORE or Software RECALL cycle is in progress. The Status Register can be modified by WRSR instruction and read by RDSR instruction. However, only the WPEN, BP1, and BP0 bits of the Status Register can be modified by using the WRSR instruction. The WRSR instruction has no effect on WEN and RDY bits. The default value shipped from the factory for WEN, BP0, BP1, bits 4-6 and WPEN bits is ‘0’. Table 3. Status Register Format Bit 7 WPEN (0) Bit 6 X (0) Bit 5 X (0) Bit 4 X (0) Bit 3 BP1 (0) Bit 2 BP0 (0) Bit 1 WEN (0) Bit 0 RDY Table 4. Status Register Bit Definition Bit Bit 0 (RDY) Bit 1 (WEN) Definition Ready Write enable Description Read only bit indicates the ready status of device to perform a memory access. This bit is set to ‘1’ by the device while a STORE or Software RECALL cycle is in progress. WEN indicates if the device is write enabled. This bit defaults to ‘0’ (disabled) on power-up. WEN = '1' --> Write enabled WEN = '0' --> Write disabled Used for block protection. For details see Table 5 on page 10. Used for block protection. For details see Table 5 on page 10. Bits are writable and volatile. On power-up, bits are written with ‘0’. Bit 2 (BP0) Bit 3 (BP1) Bit 4-6 Bit 7 (WPEN) Block protect bit ‘0’ Block protect bit ‘1’ Don’t care Write protect enable bit Used for enabling the function of write protect pin (WP). For details see Table 6 on page 11. WRSR instruction is a write instruction and needs writes to be enabled (WEN bit set to ‘1’) using the WREN instruction before it is issued. The instruction is issued after the falling edge of CS using the opcode for WRSR followed by eight bits of data to be stored in the Status Register. Since only bits 2, 3, and 7 can be modified by WRSR instruction, it is recommended to leave the bits 4-6 as ‘0’ while writing to the Status Register. Note In CY14B256P, the values written to Status Register are saved to nonvolatile memory only after a STORE operation. If AutoStore is disabled, any modifications to the Status Register must be secured by performing a Software STORE operation. Read Status Register (RDSR) Instruction The Read Status Register (RDSR) instruction provides access to the Status Register. This instruction is used to probe the write enable status of the device or the Ready status of the device. RDY bit is set by the device to ‘1’ whenever a STORE or Software RECALL cycle is in progress. The block protection and WPEN bits indicate the extent of protection employed. This instruction is issued after the falling edge of CS using the opcode for RDSR. Write Status Register (WRSR) Instruction The WRSR instruction enables the user to write to the Status Register. However, this instruction cannot be used to modify bit 0 and bit 1 (RDY and WEN). The BP0 and BP1 bits can be used to select one of four levels of block protection. Further, WPEN bit must be set to ‘1’ to enable the use of Write Protect (WP) pin. Figure 6. Read Status Register (RDSR) Instruction Timing CS 0 1 2 3 4 5 6 7 0 1 2 3 4 5 6 7 SCK SI 0 0 0 0 HI-Z 0 1 0 1 0 MSB LSB SO D7 D6 D5 D4 D3 D2 D1 D0 MSB Data LSB Document Number: 001-53881 Rev. *F Page 9 of 36 For Evaluation Samples only. Production will be supported with the next revision silicon in SOIC package. CY14B256P Figure 7. Write Status Register (WRSR) Instruction Timing CS 0 1 2 3 4 5 6 7 0 1 2 3 4 5 6 7 SCK Opcode Data in SI 0 0 0 0 HI-Z 0 0 0 1 D7 X MSB X X D3 D2 X X LSB SO Write Protection and Block Protection CY14B256P provides features for both software and hardware write protection using WRDI instruction and WP. Additionally, this device also provides block protection mechanism through BP0 and BP1 pins of the Status Register. The write enable and disable status of the device is indicated by WEN bit of the Status Register. The write instructions (WRSR, WRITE, and WRTC) and nvSRAM special instruction (STORE, RECALL, ASENB, ASDISB) need the write to be enabled (WEN bit = 1) before they can be issued. Write Disable (WRDI) Instruction Write Disable instruction disables the write by clearing the WEN bit to ‘0’ to protect the device against inadvertent writes. This instruction is issued following the falling edge of CS followed by opcode for WRDI instruction. The WEN bit is cleared on the rising edge of CS following a WRDI instruction. Figure 9. WRDI Instruction CS 0 SCK SI SO 0 0 0 0 0 1 0 0 1 2 3 4 5 6 7 Write Enable (WREN) Instruction On power-up, the device is always in the write disable state. The following WRITE, WRSR, WRTC, or nvSRAM special instruction must therefore be preceded by a Write Enable instruction. If the device is not write enabled (WEN = ‘0’), it ignores the write instructions and returns to the standby state when CS is brought HIGH. A new CS falling edge is required to re-initiate serial communication. The instruction is issued following the falling edge of CS. When this instruction is used, the WEN bit of Status Register is set to ‘1’. WEN bit defaults to ‘0’ on power-up. Note After completion of a write instruction (WRSR, WRITE, or WRTC) or nvSRAM special instruction (STORE, RECALL, ASENB, ASDISB) instruction, WEN bit is cleared to ‘0’. This is done to provide protection from any inadvertent writes. Therefore, WREN instruction must be used before a new write instruction is issued. Figure 8. WREN Instruction CS 0 SCK SI SO 0 0 0 0 0 1 1 0 1 2 3 4 5 6 7 HI-Z Block Protection Block protection is provided using the BP0 and BP1 pins of the Status Register. These bits can be set using WRSR instruction and probed using the RDSR instruction. The nvSRAM is divided into four array segments. One-quarter, one-half, or all of the memory segments can be protected. Any data within the protected segment is read only. Table 5 shows the function of block protect bits. Table 5. Block Write Protect Bits Level 0 1 (1/4) 2 (1/2) 3 (All) Status Register Bits BP1 0 0 1 1 BP0 0 1 0 1 Array Addresses Protected None 0x6000-0x7FFF 0x4000-0x7FFF 0x0000-0x7FFF HI-Z Document Number: 001-53881 Rev. *F Page 10 of 36 For Evaluation Samples only. Production will be supported with the next revision silicon in SOIC package. CY14B256P Hardware Write Protection (WP Pin) The write protect pin (WP) is used to provide hardware write protection. WP pin allows all normal read and write operations when held HIGH. When the WP pin is brought LOW and WPEN bit is ‘1’, all write operations to the Status Register are inhibited. The hardware write protection function is blocked when the WPEN bit is ‘0’. This allows the user to install the CY14B256P in a system with the WP pin tied to ground, and still write to the Status Register. WP pin can be used along with WPEN and block protect bits (BP1 and BP0) of the Status Register to inhibit writes to memory. When WP pin is LOW and WPEN is set to ‘1’, any modifications to the Status Register are disabled. Therefore, the memory is protected by setting the BP0 and BP1 bits and the WP pin inhibits any modification of the Status Register bits, providing hardware write protection. Note WP going LOW when CS is still LOW has no effect on any of the ongoing write operations to the Status Register. Table 6 summarizes all the protection features provided in the CY14B256P. Table 6. Write Protection Operation WPEN X 0 1 1 WP X X LOW HIGH Status WEN Protected Unprotected Register Blocks Blocks 0 1 1 1 Protected Protected Protected Protected Protected Writable Writable Writable Protected Writable Protected Writable opcode is transmitted through the SI line followed by two bytes of address. The MSB bit (A15) of the address is a “don’t care”. After the last address bit is transmitted on the SI pin, the data (D7-D0) at the specific address is shifted out on the SO line on the falling edge of SCK starting with D7. Any other data on SI line after the last address bit is ignored. CY14B256P allows reads to be performed in bursts through SPI which can be used to read consecutive addresses without issuing a new READ instruction. If only one byte is to be read, the CS line must be driven HIGH after one byte of data comes out. However, the read sequence may be continued by holding the CS line LOW and the address is automatically incremented and data continues to shift out on SO pin. When the last data memory address (0x7FFF) is reached, the address rolls over to 0x0000 and the device continues to read. Write Sequence (WRITE) instruction The write operations on CY14B256P are performed through the SI pin. To perform a write operation CY14B256P, if the device is write disabled, then the device must first be write enabled through the WREN instruction. When the writes are enabled (WEN = ‘1’), WRITE instruction is issued after the falling edge of CS. A WRITE instruction constitutes transmitting the WRITE opcode on SI line followed by 2 bytes of address and the data (D7-D0) which is to be written. The MSB bit (A15) of the address is a “don’t care”. CY14B256P allows writes to be performed in bursts through SPI which can be used to write consecutive addresses without issuing a new WRITE instruction. If only one byte is to be written, the CS line must be driven HIGH after the D0 (LSB of data) is transmitted. However, if more bytes are to be written, CS line must be held LOW and address is incremented automatically. The following bytes on the SI line are treated as data bytes and written in the successive addresses. When the last data memory address (0x7FFF) is reached, the address rolls over to 0x0000 and the device continues to write. The WEN bit is reset to ‘0’ on completion of a WRITE sequence. Note When a burst write reaches a protected block address, it continues the address increment into the protected space but does not write any data to the protected memory. If the address roll over takes the burst write to unprotected space, it resumes writes. The same operation is true if a burst write is initiated within a write protected block. Memory Access All memory accesses are done using the READ and WRITE instructions. These instructions cannot be used while a STORE or RECALL cycle is in progress. A STORE cycle in progress is indicated by the RDY bit of the Status Register and the HSB pin. Read Sequence (READ) instruction The read operations on CY14B256P are performed by giving the instruction on the SI pin and reading the output on SO pin. The following sequence needs to be followed for a read operation: After the CS line is pulled LOW to select a device, the read Figure 10. Read Instruction Timing CS SCK Op-Code 15-bit Address SI 0 0 0 0 0 0 1 1 X 14 13 12 11 10 9 MSB HI-Z 8 ~~ ~~ 0 1 2 3 4 5 6 7 0 1 2 3 4 5 6 7 12 13 14 15 0 1 2 3 4 5 6 7 3 2 1 0 LSB D7 D6 D5 D4 D3 D2 D1 D0 LSB Data SO MSB Document Number: 001-53881 Rev. *F Page 11 of 36 For Evaluation Samples only. Production will be supported with the next revision silicon in SOIC package. CY14B256P Figure 11. Burst Mode Read Instruction Timing CS SCK Op-Code SI 0 0 0 0 0 0 1 1 X 14 13 12 11 10 9 8 ~ ~ 15-bit Address 3 2 1 0 MSB ~ ~ LSB Data Byte 1 Data Byte N SO HI-Z MSB LSB D7 D6 D5 D4 D3 D2 D1 D0 D7 D0 D7 D6 D5 D4 D3 D2 D1 D0 ~ ~ ~ ~ 0 1 2 3 4 5 6 7 0 1 2 3 4 5 6 7 12 13 14 15 0 1 2 3 4 5 6 7 0 7 0 1 2 3 4 5 6 7 MSB LSB Figure 12. Write Instruction Timing CS SCK Op-Code 15-bit Address 1 0 X 14 13 12 11 10 9 SI ~~ ~~ 0 1 2 3 4 5 6 7 0 1 2 3 4 5 6 7 12 13 14 15 0 1 2 3 4 5 6 7 0 0 0 0 0 0 8 3 2 1 0 D7 D6 D5 D4 D3 D2 D1 D0 Data LSB MSB LSB MSB SO HI-Z Figure 13. Burst Mode Write Instruction Timing CS SCK ~ ~ ~ ~ 0 1 2 3 4 5 6 7 0 1 2 3 4 5 6 7 12 13 14 15 0 1 2 3 4 5 6 7 0 7 0 1 2 3 4 5 6 7 Data Byte 1 Data Byte N SI 0 0 0 0 0 0 1 0 X 14 13 12 11 10 9 8 ~ ~ 3 2 1 0 D7 D6 D5 D4 D3 D2 D1 D0 D7 D0 D7 D6 D5 D4 D3 D2 D1 D0 LSB MSB LSB MSB SO HI-Z Document Number: 001-53881 Rev. *F ~ ~ Op-Code 15-bit Address Page 12 of 36 For Evaluation Samples only. Production will be supported with the next revision silicon in SOIC package. CY14B256P RTC Access CY14B256P uses 16 registers for RTC. These registers can be read out or written to by accessing all 16 registers in burst mode or accessing each register, one at a time. The RDRTC and WRTC instructions are used to access the RTC. All the RTC registers can be read in burst mode by issuing the RDRTC instruction and reading all 16 bytes without bringing the CS pin HIGH. The ‘R’ bit must be set while reading the RTC timekeeping registers to ensure that transitional values of time are not read. Writes to the RTC register are performed using the WRTC instruction. Writing RTC timekeeping registers and control registers, except for the flags register needs the ‘W’ bit of the flags register to be set to ‘1’. The internal counters are updated with the new date and time setting when the ‘W’ bit is cleared to ‘0’. All the RTC registers can also be written in burst mode using the WRTC instruction. the SO pin requires the following sequence: After the CS line is pulled LOW to select a device, the RDRTC opcode is transmitted through the SI line followed by eight address bits for selecting the register. Any data on the SI line after the address bits is ignored. The data (D7-D0) at the specified address is then shifted out onto the SO line. RDRTC also allows burst mode read operation. When reading multiple bytes from RTC registers, the address rolls over to 0x00 after the last RTC register address (0x0F) is reached. The ‘R’ bit in RTC flags register must be set to '1' before reading RTC time keeping registers to avoid reading transitional data. Modifying the RTC flags register requires a Write RTC cycle. The R bit must be cleared to '0' after completion of the read operation. The easiest way to read RTC registers is to perform RDRTC in burst mode. The read may start from the first RTC register (0x00) and the CS must be held LOW to allow the data from all 16 RTC registers to be transmitted through the SO pin. Note Read RTC (RDRTC) instruction operates at a maximum clock frequency of 25 MHz. The opcode cycles, address cycles and data out cycles need to run at 25 MHz for the instruction to work properly. READ RTC (RDRTC) Instruction Read RTC (RDRTC) instruction allows the user to read the contents of RTC registers. Reading the RTC registers through Figure 14. Read RTC (RDRTC) Instruction Timing CS 0 1 2 3 4 5 6 7 0 1 2 3 4 5 6 7 0 1 2 3 4 5 6 7 SCK Op-Code SI 0 0 0 1 0 0 1 1 00 MSB 0 0 A3 A2 A1 A0 LSB D7 D6 D5 D4 D3 D2 D1 D0 MSB Data LSB SO WRITE RTC (WRTC) Instruction WRITE RTC (WRTC) instruction allows the user to modify the contents of RTC registers. The WRTC instruction requires the WEN bit to be set to '1' before it can be issued. If WEN bit is '0', a WREN instruction needs to be issued before using WRTC. Writing RTC registers requires the following sequence: After the CS line is pulled LOW to select a device, WRTC opcode is transmitted through the SI line followed by eight address bits identifying the register which is to be written to and one or more bytes of data. WRTC allows burst mode write operation. When writing more than one registers in burst mode, the address rolls over to 0x00 after the last RTC address (0x0F) is reached. Note that writing to RTC timekeeping and control registers require the W bit to be set to '1'. The values in these RTC registers take effect only after the ‘W’ bit is cleared to '0'. Write enable bit (WEN) is automatically cleared to ‘0’ after completion of the WRTC instruction. Figure 15. Write RTC (WRTC) Instruction Timing CS 0 1 2 3 4 5 6 7 0 1 2 3 4 5 6 7 0 1 2 3 4 5 6 7 SCK Op-Code 4-bit Address 1 0 0 0 0 0 SI 0 0 0 1 0 0 A3 A2 A1 A0 D7 D6 D5 D4 D3 D2 D1 D0 MSB LSB MSB HI-Z Data LSB SO Document Number: 001-53881 Rev. *F Page 13 of 36 For Evaluation Samples only. Production will be supported with the next revision silicon in SOIC package. CY14B256P nvSRAM Special Instructions CY14B256P provides four special instructions that allow access to the nvSRAM specific functions: STORE, RECALL, ASDISB, and ASENB. Table 7 lists these instructions. Table 7. nvSRAM Special Instructions Function Name STORE RECALL ASENB ASDISB Opcode 0011 1100 0110 0000 0101 1001 0001 1001 Operation Software STORE Software RECALL AutoStore Enable AutoStore Disable SCK SI SO 0 1 1 0 0 HI-Z Figure 17. Software RECALL Operation CS 0 1 2 3 4 5 6 7 0 0 0 Software STORE (STORE) instruction When a STORE instruction is executed, CY14B256P performs a Software STORE operation. The STORE operation is performed irrespective of whether a write has taken place since the last STORE or RECALL operation. Figure 16. Software STORE Operation CS 0 SCK SI SO 0 0 1 1 1 1 0 0 1 2 3 4 5 6 7 AutoStore Enable (ASENB) instruction The AutoStore Enable instruction enables the AutoStore on CY14B256P. This setting is not nonvolatile and needs to be followed by a STORE sequence if this is desired to survive the power cycle. To issue this instruction, the device must be write enabled (WEN = ‘1’). The instruction is performed by transmitting the ASENB opcode on the SI pin following the falling edge of CS. The WEN bit is cleared on the positive edge of CS following the ASENB instruction. Figure 18. AutoStore Enable Operation CS 0 SCK SI SO 0 1 0 1 1 0 0 1 1 2 3 4 5 6 7 HI-Z To issue this instruction, the device must be write enabled (WEN bit = ‘1’).The instruction is performed by transmitting the STORE opcode on the SI pin following the falling edge of CS. The WEN bit is cleared on the positive edge of CS following the STORE instruction. Software RECALL (RECALL) instruction When a RECALL instruction is executed, CY14B256P performs a Software RECALL operation. To issue this instruction, the device must be write enabled (WEN = ‘1’). HI-Z Document Number: 001-53881 Rev. *F Page 14 of 36 For Evaluation Samples only. Production will be supported with the next revision silicon in SOIC package. The instruction is performed by transmitting the RECALL opcode on the SI pin following the falling edge of CS. The WEN bit is cleared on the positive edge of CS following the RECALL instruction. CY14B256P AutoStore Disable (ASDISB) instruction AutoStore is enabled by default in CY14B256P. The AutoStore Disable instruction disables the AutoStore on CY14B256P. This setting is not nonvolatile and needs to be followed by a STORE sequence if this is desired to survive the power cycle. To issue this instruction, the device must be write enabled (WEN = ‘1’). The instruction is performed by transmitting the ASDISB opcode on the SI pin following the falling edge of CS. The WEN bit is cleared on the positive edge of CS following the ASDISB instruction. . HOLD Pin Operation Figure 19. AutoStore Disable Operation CS 0 SCK SI SO 0 0 0 1 1 0 0 1 1 2 3 4 5 6 7 Figure 20. HOLD Operation CS SCK HOLD SO ~ ~ HI-Z Document Number: 001-53881 Rev. *F Page 15 of 36 For Evaluation Samples only. Production will be supported with the next revision silicon in SOIC package. The HOLD pin is used to pause the serial communication. When the device is selected and a serial sequence is underway, HOLD is used to pause the serial communication with the master device without resetting the ongoing serial sequence. To pause, the HOLD pin must be brought LOW when the SCK pin is LOW. CS pin must remain LOW along with HOLD pin to pause serial communication. While the device serial communication is paused, inputs to the SI pin are ignored and the SO pin is in the high impedance state. To resume serial communication, the HOLD pin must be brought HIGH when the SCK pin is LOW (SCK may toggle during HOLD). CY14B256P Real Time Clock Operation nvTime Operation The CY14B256P offers internal registers that contain clock, alarm, watchdog, interrupt, and control functions. The RTC registers occupy a separate address space from nvSRAM and are accessible through Read RTC (RDRTC) and Write RTC (WRTC) instructions on register addresses 0x00 to 0x0F. Internal double buffering of the clock and the 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 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 CY14B256P consumes 0.35 µA (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. Table 8. RTC Backup Time Capacitor Value 0.1 F 0.47 F 1.0 F 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. The user must stop internal updates to the CY14B256P 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 0x00), and does not restart until a ‘0’ is written to the read bit. The RTC registers are 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 CY14B256P sources current only from the battery when the primary power is removed. However, the battery is not recharged at any time by the CY14B256P. The battery capacity must be chosen for the total anticipated cumulative down time required over the life of the system. Stopping and Starting the Oscillator The OSCEN bit in the calibration register at 0x08 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 CY14B256P has the ability to detect oscillator failure when system power is restored. This is recorded in the oscillator fail flag (OSCF) of the flags register at the address 0x00. 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 16), 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. Setting the Clock Setting the write bit ‘W’ (in the flags register at 0x00) 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 After the ‘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. Document Number: 001-53881 Rev. *F Page 16 of 36 For Evaluation Samples only. Production will be supported with the next revision silicon in SOIC package. The RTC in the CY14B256P 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. CY14B256P The value of OSCF must be reset 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 0x00) to a ‘1’ to enable writes to the flags register. Write a ‘0’ to the OSCF bit and then reset the write bit to ‘0’ to disable writes. 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 0x00 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 the flags register – 0x00) 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 CY14B256P requires the alarm match bit for seconds (0x02 - 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 the market typically have an error of +20 ppm to +35 ppm. However, CY14B256P 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. 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 0x08. 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 every 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. To determine the required calibration, the CAL bit in the flags register (0x00) 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 0x00) 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. 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 0x07 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 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 21 on page 18. 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 the user reads the flags register. Alarm The alarm function compares user programmed values of alarm time and date (stored in the registers 0x01-5) 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. Document Number: 001-53881 Rev. *F Page 17 of 36 For Evaluation Samples only. Production will be supported with the next revision silicon in SOIC package. CY14B256P Figure 21. Watchdog Timer Block Diagram . Oscillator 32,768 KHz Clock Divider 32 Hz 1 Hz Counter Zero Compare WDF Interrupts are only generated while working on normal power and are not triggered when system is running in backup power mode. Note CY14B256P generates valid interrupts only after the Power-up RECALL sequence is completed. All events on INT pin must be ignored for tFA duration after powerup. WDS Load Register D Q WDW Q Interrupt Register Watchdog Register write to Watchdog 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. 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 10 k 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 register is read. When an enabled interrupt source activates the INT pin, an external host reads the flags registers to determine the cause. Remember that 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, the flags register is not read during a reset. Power Monitor The CY14B256P provides a power management scheme with the 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 section 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 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 or Power-Up RECALL on page 29). Interrupts The CY14B256P has a 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 (0x06). In addition, each has an associated flag bit in the flags register (0x00) 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 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 after 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 16) Document Number: 001-53881 Rev. *F Page 18 of 36 For Evaluation Samples only. Production will be supported with the next revision silicon in SOIC package. 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. CY14B256P Accessing the Real Time Clock through SPI CY14B256P uses 16 registers for RTC. These registers can be read out or written to by accessing all 16 registers in burst mode or accessing each register, one at a time. The RDRTC and WRTC instructions are used to access the RTC. All the RTC registers can be read in burst mode by issuing the RDRTC instruction and reading all 16 bytes without bringing the CS pin HIGH. The ‘R’ bit must be set while reading the RTC timekeeping registers to ensure that transitional values of time are not read. Writes to the RTC register are performed using the WRTC instruction. Writing RTC timekeeping registers and control registers, except for the flags register needs the ‘W’ bit of the flags register to be set to ‘1’. The internal counters are updated with the new date and time setting when the ‘W’ bit is cleared to ‘0’. All the RTC registers can also be written in burst mode using the WRTC instruction. Figure 22. RTC Recommended Component Configuration Recommended Values Y1 = 32.768 KHz (12.5 pF) C1 = 10 pF C2 = 67 pF C1 Y1 C2 Xout Xin Note: The recommended values for C1 and C2 include board trace capacitance. Figure 23. Interrupt Block Diagram WDF Watchdog Timer WIE P/L PF VCC Power Monitor PFE Pin Driver H/L INT VINT 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 AF Clock Alarm AIE Document Number: 001-53881 Rev. *F Page 19 of 36 For Evaluation Samples only. Production will be supported with the next revision silicon in SOIC package. CY14B256P Table 9. RTC Register Map[2, 3] Register 0x0F 0x0E 0x0D 0x0C 0x0B 0x0A 0x09 0x08 0x07 0x06 0x05 0x04 0x03 0x02 0x01 0x00 WDF 0 0 0 0 0 0 OSCEN (0) WIE (0) M (1) M (1) M (1) M (1) 0 D7 D6 0 0 0 0 D5 0 D4 10s months 0 0 D3 D2 Years Months Day of month Day of week Hours Minutes Seconds Calibration (00000) WDT (000000) PFE (0) 0 H/L (1) P/L (0) 0 0 10s alarm date 10s alarm hours 10s alarm minutes 10s alarm seconds 10s centuries AF PF OSCF[5] 0 Alarm, day Alarm, hours Alarm, minutes Alarm, seconds Centuries CAL (0) W (0) R (0) D1 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 [4] Watchdog [4] Interrupts [4] Alarm, day of month: 01–31 Alarm, hours: 00–23 Alarm, minutes: 00–59 Alarm, seconds: 00–59 Centuries: 00–99 Flags [4] 10s years 10s day of month 0 10s minutes 10s seconds Cal sign (0) 10s hours WDS (0) WDW (0) AIE (0) 0 0 Notes 2. ( ) designates values shipped from the factory. 3. The unused bits of RTC registers are reserved for future use and should be set to ‘0’. 4. This is a binary value, not a BCD value. 5. When user resets OSCF flag bit, the flags register will be updated after tRTCp time. Document Number: 001-53881 Rev. *F Page 20 of 36 For Evaluation Samples only. Production will be supported with the next revision silicon in SOIC package. BCD Format Data CY14B256P Table 10. Register Map Detail Time Keeping - Years 0x0F D7 D6 10s years D5 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. Time Keeping - Months 0x0E 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. Time Keeping - Date D7 0x0D 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. Time Keeping - Day D7 D6 0 D5 0 D4 0 D3 0 D2 D1 Day of week D0 0x0C 0 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 0 D6 0 D5 10s hours D4 D3 D2 Hours D1 D0 0x0B 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 0x0A 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. Time Keeping - Seconds 0x09 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. Calibration/Control 0X08 OSCEN D7 OSCEN D6 0 D5 Calibration sign 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. Calibration Determines if the calibration adjustment is applied as an addition (1) to or as a subtraction (0) from the time-base. sign Calibration These five bits control the calibration of the clock. Document Number: 001-53881 Rev. *F Page 21 of 36 For Evaluation Samples only. Production will be supported with the next revision silicon in SOIC package. Register Description CY14B256P Table 10. Register Map Detail (continued) Watchdog Timer 0x07 WDS WDW D7 WDS D6 WDW D5 D4 D3 WDT D2 D1 D0 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 enables 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 17. 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 WDT 0x06 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 alarm match 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 0x05 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. Alarm - Hours 0x04 D7 M D6 0 D5 D4 D3 D2 D1 Alarm hours D0 10s 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 0x03 D7 M D6 D5 10s alarm minutes D4 D3 D2 D1 D0 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. Document Number: 001-53881 Rev. *F Page 22 of 36 For Evaluation Samples only. Production will be supported with the next revision silicon in SOIC package. Register Description CY14B256P Table 10. Register Map Detail (continued) Alarm - Seconds 0x02 D7 M D6 D5 10s alarm seconds D4 D3 D2 D1 D0 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 0x01 D7 D6 D5 10s centuries D4 D3 D2 D1 Centuries D0 Contains the BCD value of centuries. Lower nibble contains the lower digit and operates from 0 to 9; upper nibble contains the upper digit and operates from 0 to 9. The range for the register is 0-99 centuries. Flags 0x00 WDF AF PF OSCF D7 WDF 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 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. 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. 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 Document Number: 001-53881 Rev. *F Page 23 of 36 For Evaluation Samples only. Production will be supported with the next revision silicon in SOIC package. Register Description CY14B256P 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: ■ 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 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 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 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 maximum 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. 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. ■ ■ Document Number: 001-53881 Rev. *F Page 24 of 36 For Evaluation Samples only. Production will be supported with the next revision silicon in SOIC package. CY14B256P Maximum Ratings Exceeding maximum ratings may shorten the useful life of the device. These user guidelines are not tested. Storage temperature ................................ –65 °C to +150 °C Maximum accumulated storage time 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 DC voltage applied to outputs in high Z state ...................................... –0.5 V to VCC + 0.5 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 Package power dissipation capability (TA = 25 °C) .................................................. 1.0 W Surface mount lead soldering temperature (3 Seconds).......................................... +260 °C DC output current (1 output at a time, 1 s duration). ... 15 mA Static discharge voltage.......................................... > 2001 V (per MIL-STD-883, method 3015) Latch up current..................................................... > 200 mA Operating Range Range Industrial Ambient Temperature –40 °C to +85 °C 2.7 V to 3.6 V VCC DC Electrical Characteristics Over the Operating Range Parameter VCC ICC1 ICC2 ICC4 ISB IIX[7] Description Power supply voltage Average Vcc current Average VCC current during STORE At fSCK = 40 MHz. Values obtained without output loads (IOUT = 0 mA) All inputs don’t care, VCC = Max Average current for duration tSTORE Test Conditions Min 2.7 – – – – –1 –100 –1 2.0 VSS – 0.5 2.4 – 61 IOUT = 4 mA Between VCAP pin and VSS, 5 V rated Typ[6] 3.0 – – – – – – – – – – – 68 0.4 180 Max 3.6 10 10 5 5 +1 +1 +1 VCC + 0.5 0.8 Unit V mA mA mA mA µA µA µA V V V V µF Average VCAP current All inputs don’t care. Average current for duration tSTORE during AutoStore cycle VCC standby current CS > (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. Input leakage current VCC = Max, VSS < VIN < VCC (except HSB) Input leakage current VCC = Max, VSS < VIN < VCC (for HSB) IOZ VIH VIL VOH VOL VCAP[8] Off state output leakage current Input HIGH voltage Input LOW voltage VCC = Max, VSS < VOUT < VCC Output HIGH voltage IOUT = –2 mA Output LOW voltage Storage capacitor Notes 6. Typical values are at 25 °C, VCC= VCC (Typ). Not 100% tested. 7. The HSB pin has IOUT = –2 µA for VOH of 2.4 V 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. 8. Min VCAP value guarantees that there is a sufficient charge available to complete a successful AutoStore operation. Max VCAP value guarantees that the capacitor on VCAP is charged to a minimum voltage during a Power-Up RECALL cycle so that an immediate power-down cycle can complete a successful AutoStore. Therefore it is always recommended to use a capacitor within the specified min and max limits. Refer application note AN43593 for more details on VCAP options. Document Number: 001-53881 Rev. *F Page 25 of 36 For Evaluation Samples only. Production will be supported with the next revision silicon in SOIC package. CY14B256P Data Retention and Endurance Over the Operating Range 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 pin capacitance Test Conditions TA = 25 °C, f = 1 MHz, VCC = VCC (Typ) Max 6 8 Unit pF pF Thermal Resistance Parameter[9] θJA θJC 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, per EIA / JESD51. 16-SOIC 55.17 2.64 Unit °C/W °C/W Figure 24. AC Test Loads and Waveforms 3.0 V OUTPUT 30 pF 577 Ω R1 R2 789 Ω 3.0 V OUTPUT 5 pF 577 Ω R1 R2 789 Ω AC Test Conditions Input pulse levels.................................................... 0 V to 3 V Input rise and fall times (10% to 90%)......................... < 3 ns Input and output timing reference levels........................ 1.5 V Note 9. These parameters are guaranteed by design and are not tested. Document Number: 001-53881 Rev. *F Page 26 of 36 For Evaluation Samples only. Production will be supported with the next revision silicon in SOIC package. CY14B256P RTC Characteristics Over the Operating Range Parameter VRTCbat IBAK [11] Description RTC battery pin voltage RTC backup current TA (Min) 25 °C TA (Max) RTC capacitor pin voltage TA (Min) 25 °C TA (Max) Min 1.8 – – – 1.6 1.5 1.4 – – 350 Typ[10] 3.0 – 0.35 – – 3.0 – 1 – – Max 3.6 0.35 – 0.5 3.6 3.6 3.6 2 350 850 Units V µA µA µA V V V sec μs Ω VRTCcap[12] tOCS tRTCp RBKCHG RTC oscillator time to start RTC processing time from end of ‘W’ bit set to ‘0’ RTC backup capacitor charge current-limiting resistor AC Switching Characteristics Over the Operating Range[13] Cypress Parameter fSCK tCL tCH tCS tCSS tCSH tSD tHD tHH tSH tCO tHHZ[15] [15] Alt. Parameter fSCK tWL tWH tCE tCES tCEH tSU tH tHD tCD tV tHZ tLZ tHO tDIS Description Clock frequency, SCK Clock pulse width LOW Clock pulse width HIGH CS HIGH time CS setup time CS hold time Data in setup time Data in hold time HOLD hold time HOLD setup time Output valid HOLD to output high Z HOLD to output low Z Output hold time Output disable time 40 MHz Min – 11 11 20 10 10 5 5 5 5 – – – 0 – Max 40 – – – – – – – – – 9 15 15 – 25 25 MHz (RDRTC Instruction)[14] Min – 18 18 20 10 10 5 5 5 5 – – – 0 Max 25 – – – – – – – – – 15 15 15 – 25 Unit MHz ns ns ns ns ns ns ns ns ns ns ns ns ns ns tHLZ tOH tHZCS Notes 10. Typical values are at 25 °C, VCC= VCC (Typ). Not 100% tested. 11. Current drawn from either VRTCcap or VRTCbat when VCC < VSWITCH. 12. If VRTCcap > 0.5 V or if no capacitor is connected to VRTCcap pin, the oscillator starts in tOCS time. If a backup capacitor is connected and VRTCcap < 0.5 V, the capacitor must be allowed to charge to 0.5 V for oscillator to start. 13. Test conditions assume signal transition time of 3 ns or less, timing reference levels of VCC/2, input pulse levels of 0 to VCC (typ), and output loading of the specified IOL/IOH and load capacitance shown in Figure 24. 14. Applicable for RTC opcode cycles, address cycles, and dataout cycles. 15. These parameters are guaranteed by design and are not tested. Document Number: 001-53881 Rev. *F Page 27 of 36 For Evaluation Samples only. Production will be supported with the next revision silicon in SOIC package. CY14B256P Figure 25. Synchronous Data Timing (Mode 0) tCS CS tCSS tCH tCL tCSH SCK tSD tHD SI VALID IN tCO tOH tHZCS SO HI-Z HI-Z Figure 26. HOLD Timing CS SCK tHH tSH HOLD tHHZ SO tHH tSH tHLZ Document Number: 001-53881 Rev. *F Page 28 of 36 For Evaluation Samples only. Production will be supported with the next revision silicon in SOIC package. ~ ~ ~ ~ CY14B256P AutoStore or Power-Up RECALL Over the Operating Range Parameter tFA [16] tSTORE [17] 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 high to nvSRAM active time HSB high active time CY14B256P Min – – – – 150 – – – Max 20 8 25 2.65 – 1.9 5 500 Unit ms ms ns V µs V µs ns VHDIS[19] tLZHSB[19] tHHHD[19] tDELAY [18] VSWITCH tVCCRISE[19] Switching Waveforms VCC VSWITCH VHDIS Figure 27. AutoStore or Power-Up RECALL[20] t VCCRISE 21 tHHHD Note 17 tSTORE tHHHD Note 17 tSTORE 21 Note HSB OUT Note tDELAY AutoStore tLZHSB tDELAY tLZHSB POWERUP RECALL Read & Write Inhibited (RWI) POWER-UP RECALL tFA tFA Read & Write BROWN OUT AutoStore POWER-UP RECALL Read & Write POWER DOWN AutoStore Notes 16. tFA starts from the time VCC rises above VSWITCH. 17. If an SRAM write has not taken place since the last nonvolatile cycle, no AutoStore or Hardware STORE takes place. 18. On a Hardware STORE and AutoStore initiation, SRAM write operation continues to be enabled for time tDELAY. 19. These parameters are guaranteed by design and are not tested. 20. Read and Write cycles are ignored during STORE, RECALL, and while VCC is below VSWITCH. 21. During power up and power down, HSB glitches when HSB pin is pulled up through an external resistor. Document Number: 001-53881 Rev. *F Page 29 of 36 For Evaluation Samples only. Production will be supported with the next revision silicon in SOIC package. CY14B256P Software Controlled STORE/RECALL Cycles Over the Operating Range Parameter tRECALL tSS [22, 23] Description RECALL duration Soft sequence processing time CY14B256P Min – – Max 200 100 Unit µs µs Figure 28. Software STORE Cycle[23] Figure 29. Software RECALL Cycle[23] CS 0 SCK SI 0 0 1 1 1 1 0 0 tSTORE CS 1 2 3 4 5 6 7 SCK SI 0 1 1 0 0 0 0 0 tRECALL 0 1 2 3 4 5 6 7 RWI RDY HI-Z RWI RDY HI-Z Figure 30. AutoStore Enable Cycle Figure 31. AutoStore Disable Cycle CS 0 SCK SI 0 1 0 1 1 0 0 1 tSS CS 1 2 3 4 5 6 7 SCK SI 0 0 0 1 1 0 0 1 tSS 0 1 2 3 4 5 6 7 RWI RDY HI-Z RWI RDY HI-Z Notes 22. 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. 23. Commands such as STORE and RECALL lock out I/O until operation is complete which further increases this time. See the specific command. Document Number: 001-53881 Rev. *F Page 30 of 36 For Evaluation Samples only. Production will be supported with the next revision silicon in SOIC package. CY14B256P Hardware STORE Cycle Over the Operating Range Parameter tPHSB Description Hardware STORE pulse width Figure 32. Hardware STORE Cycle[24] CY14B256P Min 15 Max – Unit ns Write Latch set HSB (IN) tDELAY HSB (OUT) tSTORE ~ ~ tPHSB tHHHD tLZHSB RWI Write Latch not set HSB (IN) ~ ~ tPHSB HSB pin is driven HIGH to VCC only by Internal 100 K resistor, HSB driver is disabled SRAM is disabled as long as HSB (IN) is driven LOW. HSB (OUT) tDELAY RWI Note 24. If an SRAM write has not taken place since the last nonvolatile cycle, no AutoStore or Hardware STORE takes place. Document Number: 001-53881 Rev. *F Page 31 of 36 For Evaluation Samples only. Production will be supported with the next revision silicon in SOIC package. ~ ~ ~ ~ CY14B256P Ordering Information Ordering Code CY14B256P-SFXIT CY14B256P-SFXI All the above parts are Pb-free. Package Diagram 51-85022 16-pin SOIC Package Type Operating Range Industrial Ordering Code Definition CY 14 B 256 P - SF X I T Option: T - Tape and Reel Blank - Std. Pb-free Package: SF - 16 SOIC Temperature: I - Industrial (–40 °C to 85 °C) P - Serial (SPI) nvSRAM with RTC Density: Voltage: B - 3.0 V 14 - nvSRAM Cypress 256 - 256 Kb Document Number: 001-53881 Rev. *F Page 32 of 36 For Evaluation Samples only. Production will be supported with the next revision silicon in SOIC package. CY14B256P Package Diagram Figure 33. 16-pin (300 mil) SOIC Package 51-85022 *C Document Number: 001-53881 Rev. *F Page 33 of 36 For Evaluation Samples only. Production will be supported with the next revision silicon in SOIC package. CY14B256P Acronyms Acronym BCD CMOS CRC CPHA CPOL EEPROM EIA I/O JEDEC nvSRAM RoHS RWI SOIC SONOS SPI Description Binary coded decimal Complementary metal oxide semiconductor Cyclic redundancy check Clock phase Clock polarity Electrically erasable programmable read-only memory Electronic Industries Alliance Input/output Joint Electron Devices Engineering Council nonvolatile static random access memory Restriction of hazardous substances Read and write inhibited Small outline integrated circuit Silicon-oxide-nitride-oxide-silicon Serial peripheral interface Document Conventions Units of Measure Symbol °C Hz KΩ µA µF µs mA MHz ns Ω pF V W degree Celsius Hertz kilo ohm micro Amperes micro Farad micro second milli Amperes Mega Hertz nano seconds ohm pico Farad Volts Watts Unit of Measure Document Number: 001-53881 Rev. *F Page 34 of 36 For Evaluation Samples only. Production will be supported with the next revision silicon in SOIC package. CY14B256P Document History Page Document Title: CY14B256P 256-Kbit (32 K x 8) Serial (SPI) nvSRAM with Real Time Clock Document Number: 001-53881 Revision ** *A ECN 2733272 2758444 Orig. of Change GVCH/AESA GVCH Submission Date 07/16/09 09/01/09 New Datasheet Moved data sheet status from preliminary to Final Removed commercial temperature related specs Added thermal resistance values for 16-SOIC package Added note to Write Sequence (WRITE) description Changed VRTCbat max value from 3.3 V to 3.6 V Changed RBKCHG min value from 450 Ω to 350 Ω Updated footnote 8 Changed STORE cycles to QuantumTrap from 200 K to 1 Million Updated Figure 2 Updated IBAK RTC backup current spec unit from nA to μA Added Contents Changed ground naming convention from GND to VSS Table 1: Added more clarity on HSB pin operation Hardware STORE and HSB Pin Operation: Added more clarity on HSB pin operation Updated Power-Down description Power On Reset: Added status of bits 4-6 Table 4: Added definition of bits 4-6 Updated Figure 7, Figure 25, Figure 26, and Figure 27 Updated footnote 19 Added Figure 30 and Figure 31 Removed tDHSB parameter Updated Figure 32 Updated Package Diagram Added Acronyms and Document Conventions. Added watermark as “For Evaluation Samples only. Production will be supported with the next revision silicon in SOIC package.” Updated HOLD Pin Operation, Figure 20 and Figure 26 to indicate that CS pin must remain LOW along with HOLD pin to pause serial communication. Hardware STORE and HSB Pin Operation: Added more clarity on HSB pin operation Updated Setting the Clock description Updated ‘W’ bit description in Register Map Detail table Updated Best Practices Added tRTCp parameter to RTC Characteristics table Updated tLZHSB parameter description Fixed typo in Figure 27. Added footnote 8 and 13. Description of Change *B 2839453 GVCH/PYRS 01/06/10 *C 3008637 GVCH 08/16/10 *D 3033665 GVCH 09/24/10 *E 3143330 GVCH 01/17/11 *F 3320715 GVCH 07/19/11 Document Number: 001-53881 Rev. *F Page 35 of 36 For Evaluation Samples only. Production will be supported with the next revision silicon in SOIC package. CY14B256P Sales, Solutions, and Legal Information Worldwide Sales and Design Support Cypress maintains a worldwide network of offices, solution centers, manufacturer’s representatives, and distributors. To find the office closest to you, visit us at Cypress Locations. Products Automotive Clocks & Buffers Interface Lighting & Power Control Memory Optical & Image Sensing PSoC Touch Sensing USB Controllers Wireless/RF cypress.com/go/automotive cypress.com/go/clocks cypress.com/go/interface cypress.com/go/powerpsoc cypress.com/go/plc cypress.com/go/memory cypress.com/go/image cypress.com/go/psoc cypress.com/go/touch cypress.com/go/USB cypress.com/go/wireless PSoC Solutions psoc.cypress.com/solutions PSoC 1 | PSoC 3 | PSoC 5 © 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 Number: 001-53881 Rev. *F Revised July 19, 2011 Page 36 of 36 All products and company names mentioned in this document may be the trademarks of their respective holders. For Evaluation Samples only. Production will be supported with the next revision silicon in SOIC package.