Cypress CY14B108M, CY14B108K manual Device Operation, Sram Read, Sram Write, AutoStore Operation

				PRELIMINARY			CY14B108K, CY14B108M
Table 1. Pin Definitions (continued)
Pin Name		I/O Type				Description
	INT	Output	Interrupt Output. Programmable to respond to the clock alarm, the watchdog timer, and the power
			monitor. Also programmable to either active HIGH (push or pull) or LOW (open drain).
	VSS	Ground	Ground for the Device. Must be connected to ground of the system.
	VCC	Power Supply	Power Supply Inputs to the Device. 3.0V +20%, –10%.
		Input/Output	Hardware STORE Busy		(HSB)	. When LOW this output indicates that a Hardware STORE is in progress.
	HSB		When pulled LOW external to the chip it initiates a nonvolatile STORE operation. A weak internal pull
			up resistor keeps this pin HIGH if not connected (connection optional). After each STORE operation
			HSB is driven HIGH for short time with standard output high current.
VCAP		Power Supply	AutoStore Capacitor. Supplies power to the nvSRAM during power loss to store data from SRAM to
			nonvolatile elements.

Device Operation

The CY14B108K/CY14B108M nvSRAM is made up of two functional components paired in the same physical cell. These are a SRAM memory cell and a nonvolatile QuantumTrap cell. The SRAM memory cell operates as a standard fast static RAM. Data in the SRAM is transferred to the nonvolatile cell (the STORE operation), or from the nonvolatile cell to the SRAM (the RECALL operation). Using this unique architecture, all cells are stored and recalled in parallel. During the STORE and RECALL operations SRAM read and write operations are inhibited. The CY14B108K/CY14B108M supports infinite reads and writes similar to a typical SRAM. In addition, it provides infinite RECALL operations from the nonvolatile cells and up to 200K STORE operations. See the Truth Table For SRAM Operations on page 24 for a complete description of read and write modes.

SRAM Read

The CY14B108K/CY14B108M performs a read cycle whenever CE and OE are LOW, and WE and HSB are HIGH. The address specified on pins A0-19or A0-18determines which of the 1,048,576 data bytes or 524,288 words of 16 bits each are accessed. Byte enables (BHE, BLE) determine which bytes are enabled to the output, in the case of 16-bit words. When the read is initiated by an address transition, the outputs are valid after a delay of tAA (read cycle 1). If the read is initiated by CE or OE, the outputs are valid at tACE or at tDOE, whichever is later (read cycle 2). The data output repeatedly responds to address changes within the tAA access time without the need for transi- tions on any control input pins. This remains valid until another address change or until CE or OE is brought HIGH, or WE or HSB is brought LOW.

SRAM Write

A write cycle is performed when CE and WE are LOW and HSB is HIGH. The address inputs must be stable before entering the write cycle and must remain stable until CE or WE goes HIGH at the end of the cycle. The data on the common I/O pins DO0-15are written into the memory if it is valid tSD before the end of a WE controlled write or before the end of a CE controlled write. The Byte Enable inputs (BHE, BLE) determine which bytes are written, in the case of 16-bit words. Keep OE HIGH during the entire write cycle to avoid data bus contention on common I/O lines. If OE is left LOW, internal circuitry turns off the output buffers tHZWE after WE goes LOW.

Document #: 001-47378 Rev. **

AutoStore Operation

The CY14B108K/CY14B108M stores data to the nvSRAM using one of three storage operations. These three operations are: Hardware STORE, activated by the HSB; Software STORE, activated by an address sequence; AutoStore, on device power down. The AutoStore operation is a unique feature of QuantumTrap technology and is enabled by default on the CY14B108K/CY14B108M.

During normal operation, the device draws current from VCC to charge a capacitor connected to the VCAP pin. This stored charge is used by the chip to perform a single STORE operation. If the voltage on the VCC pin drops below VSWITCH, the part automatically disconnects the VCAP pin from VCC. A STORE operation is initiated with power provided by the VCAP capacitor.

Figure 2. AutoStore Mode

Vcc

0.1uF

10kOhm Vcc

WEVCAP

VSS VCAP

Figure 2 shows the proper connection of the storage capacitor (VCAP) for automatic STORE operation. Refer to DC Electrical Characteristics on page 15 for the size of the VCAP. The voltage on the VCAP pin is driven to VCC by a regulator on the chip. A pull up should be placed on WE to hold it inactive during power up. This pull up is only effective if the WE signal is tri-state during power up. Many MPUs tri-state their controls on power up. Verify this when using the pull up. When the nvSRAM comes out of

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