Cypress CY7C1470BV25, CY7C1474BV25, CY7C1472BV25 manual Functional Overview

			CY7C1470BV25
			CY7C1472BV25, CY7C1474BV25
Table 1. Pin Definitions (continued)
Pin Name	IO Type		Pin Description
TMS	Test Mode Select	TMS Pin Controls the Test Access Port State Machine. Sampled on the rising edge of TCK.
	Synchronous
TCK	JTAG Clock	Clock Input to the JTAG Circuitry.
VDD	Power Supply	Power Supply Inputs to the Core of the Device.
VDDQ	IO Power Supply	Power Supply for the IO Circuitry.
VSS	Ground	Ground for the Device. Must be connected to ground of the system.
NC	–	No Connects. This pin is not connected to the die.
NC(144M,	–	These Pins are Not Connected. They are used for expansion to the 144M, 288M, 576M, and 1G
288M,		densities.
576M, 1G)
ZZ	Input-	ZZ “Sleep” Input. This active HIGH input places the device in a non-time critical “sleep” condition
	Asynchronous	with data integrity preserved. For normal operation, this pin has must be LOW or left floating.
		ZZ pin has an internal pull down.

Functional Overview

The CY7C1470BV25, CY7C1472BV25, and CY7C1474BV25 are synchronous-pipelined Burst NoBL SRAMs designed specif- ically to eliminate wait states during read or write 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. All data outputs pass through output registers controlled by the rising edge of the clock. Maximum access delay from the clock rise (tCO) is 3.0 ns (250-MHz device).

Accesses can be 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). BW[x] can be used to conduct Byte Write opera- tions.

Write operations are qualified by the Write Enable (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) the input signal 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 core and control logic. The control logic determines that a read access is in progress and allows the requested data to propagate to the input of the output register. At the rising edge of the next clock the requested data is allowed to propagate through the output

register and onto the data bus within 2.6 ns (250-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. During the second clock, a subsequent operation (read, write, or deselect) can be initiated. Deselecting the device is also pipelined. Therefore, when the SRAM is deselected at clock rise by one of the chip enable signals, its output tri-states following the next clock rise.

Burst Read Accesses

The CY7C1470BV25, CY7C1472BV25, and CY7C1474BV25 have an on-chip burst counter that enables the user 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 Accesses section. The sequence of the burst counter is deter- mined by the MODE input signal. A LOW input on MODE selects a linear burst mode, a HIGH selects an interleaved 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 enables 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 the following conditions are satisfied at clock rise: (1) CEN is asserted LOW, (2) CE1, CE2, and CE3 are ALL asserted active, and (3) the signal WE is asserted LOW. The address presented to the address inputs is loaded into the Address Register. The write signals are latched into the Control Logic block.

On the subsequent clock rise 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 DQ and DQP (DQa,b,c,d/DQPa,b,c,d for CY7C1470BV25, DQa,b/DQPa,b for CY7C1472BV25, and DQa,b,c,d,e,f,g,h/DQPa,b,c,d,e,f,g,h for CY7C1474BV25). In addition, the address for the subsequent

Document #: 001-15032 Rev. *D Page 8 of 29

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