Cypress CY7C1473V25, CY7C1475V25 Functional Overview, Single Read Accesses, Burst Read Accesses

		CY7C1471V25
		CY7C1473V25
		CY7C1475V25
Pin Definitions (continued)
Name	IO	Description
TDI	JTAG serial input	Serial data-In to the JTAG circuit. Sampled on the rising edge of TCK. If the JTAG feature
	Synchronous	is not used, this pin can be left floating or connected to VDD through a pull up resistor. This
		pin is not available on TQFP packages.
TMS	JTAG serial input	Serial data-In to the JTAG circuit. Sampled on the rising edge of TCK. If the JTAG feature
	Synchronous	is not used, this pin can be disconnected or connected to VDD. This pin is not available on
		TQFP packages.
TCK	JTAG-Clock	Clock input to the JTAG circuitry. If the JTAG feature is not used, this pin must be
		connected to VSS. This pin is not available on TQFP packages.
NC	-	No Connects. Not internally connected to the die. 144M, 288M, 576M, and 1G are address
		expansion pins and are not internally connected to the die.

Functional Overview

The CY7C1471V25, CY7C1473V25, and CY7C1475V25 are synchronous flow through burst SRAMs designed specifically to eliminate wait states during write-read transitions. All synchronous inputs pass through input registers controlled by the rising edge of the clock. The clock signal is qualified with the Clock Enable input signal (CEN). If CEN is HIGH, the clock signal is not recognized and all internal states are maintained. All synchronous operations are qualified with CEN. Maximum access delay from the clock rise (tCDV) is 6.5 ns (133-MHz device).

Accesses are initiated by asserting all three Chip Enables (CE1, CE2, CE3) active at the rising edge of the clock. If CEN is active LOW and ADV/LD is asserted LOW, the address presented to the device is latched. The access can either be a read or write operation, depending on the status of the Write Enable (WE). Byte Write Select (BWX) can be used to conduct Byte Write operations.

Write operations are qualified by the WE. All writes are simplified with on-chip synchronous self timed write circuitry.

Three synchronous Chip Enables (CE1, CE2, CE3) and an asynchronous Output Enable (OE) simplify depth expansion. All operations (reads, writes, and deselects) are pipelined. ADV/LD must be driven LOW after the device is deselected to load a new address for the next operation.

Single Read Accesses

A read access is initiated when the following conditions are satisfied at clock rise: (1) CEN is asserted LOW, (2) CE1, CE2, and CE3 are ALL asserted active, (3) WE is deasserted HIGH, and (4) ADV/LD is asserted LOW. The address presented to the address inputs is latched into the Address Register and presented to the memory array and control logic. The control logic determines that a read access is in progress and allows the requested data to propagate to the output buffers. The data is available within 6.5 ns (133-MHz device) provided OE is active LOW. After the first clock of the read access, the output buffers are controlled by OE and the internal control logic. OE must be driven LOW to drive out the requested data. On the subsequent clock, another operation (read/write/deselect) can be initiated. When the SRAM is deselected at clock rise by one of the chip enable signals, the output is tri-stated immediately.

Burst Read Accesses

The CY7C1471V25, CY7C1473V25, and CY7C1475V25 has an on-chip burst counter that enables the user the ability to supply a single address and conduct up to four reads without reasserting the address inputs. ADV/LD must be driven LOW to load a new address into the SRAM, as described in the Single Read Access section. The sequence of the burst counter is determined by the MODE input signal. A LOW input on MODE selects a linear burst mode, a HIGH selects an inter- leaved burst sequence. Both burst counters use A0 and A1 in the burst sequence, and wraps around when incremented sufficiently. A HIGH input on ADV/LD increments the internal burst counter regardless of the state of chip enable inputs or WE. WE is latched at the beginning of a burst cycle. Therefore, the type of access (read or write) is maintained throughout the burst sequence.

Single Write Accesses

Write accesses are initiated when these conditions are satisfied at clock rise:

•CEN is asserted LOW

•CE1, CE2, and CE3 are ALL asserted active

•WE is asserted LOW.

The address presented to the address bus is loaded into the Address Register. The write signals are latched into the Control Logic block. The data lines are automatically tri-stated regardless of the state of the OE input signal. This allows the external logic to present the data on DQs and DQPX.

On the next clock rise the data presented to DQs and DQPX (or a subset for Byte Write operations, see “Truth Table for Read/Write” on page 12 for details) inputs is latched into the device and the write is complete. Additional accesses (read/write/deselect) can be initiated on this cycle.

The data written during the write operation is controlled by BWX signals. The CY7C1471V25, CY7C1473V25, and CY7C1475V25 provide Byte Write capability that is described in the “Truth Table for Read/Write” on page 12. The input WE with the selected BWx input selectively writes to only the desired bytes. Bytes not selected during a Byte Write operation remain unaltered. A synchronous self timed write mechanism is provided to simplify the write operations. Byte Write capability is included to greatly simplify read/modify/write sequences, which can be reduced to simple byte write operations.

Document #: 38-05287 Rev. *I Page 9 of 32

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