Cypress CY7C1330AV25 Introduction, Sleep Mode, PRELIMINARYCY7C1332AV25, Pipelined Read Accesses

CY7C1330AV25

PRELIMINARYCY7C1332AV25

Introduction

Functional Overview

The CY7C1330AV25 and CY7C1332AV25 are synchronous- pipelined Late Write SRAMs running at speeds up to 250 MHz. All synchronous inputs pass through input registers controlled by the rising edge of the clock. All data outputs pass through output registers controlled by the rising edge of the clock. Maximum access delay from the clock rise (tCO) is 2.0 ns (250-MHz device).

Accesses can be initiated by asserting Chip Enable (CE) on the rising edge of the clock. The address presented to the device will be latched on this edge of the clock. The access can either be a read or write operation, depending on the status of the Write Enable (WE). BWS[d:a] can be used to conduct individual byte write operations.

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

All operations (Reads, Writes, and Deselects) are pipelined.

Pipelined Read Accesses

A read access is initiated when the following conditions are satisfied at clock rise: (1) Chip Enable (CE) is asserted active and (2) the Write Enable input signal (WE) is asserted HIGH. 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 2.0 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 in order for the device to drive out the requested data. During the second clock, a subsequent operation (Read/Write/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 will tri-state following the next clock rise.

Bypass Read Operation

Bypass read operation occurs when the last write operation is followed by a read operation where write and read addresses are identical. The data outputs are provided from the data in registers rather than the memory array. This operation occurs on a byte to byte basis. If only one byte is written during a write operation and a read operation is performed on the same address; then a partial bypass read operation is performed since the new byte data will be from the datain registers while the remaining bytes are from the memory array.

Late Write Accesses

The Late Write feature allows for the write data to be presented one cycle later after the access is started. This feature elimi- nates one bus-turnaround cycle which is necessary when going from a read to a write in an ordinary pipelined Synchronous Burst SRAM.

Write access is initiated when the following conditions are satisfied at clock rise: (1) CE is asserted active and (2) the write signal WE is asserted LOW. The address presented to

Ax 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 when a write is detected. This allows the external logic to present the data on DQ and DQP (DQ[a:b] for CY7C1332AV25 and DQ[a:d] for CY7C1330AV25). In addition, the address for the subsequent access (Read/Write/Deselect) is latched into the Address Register (provided the appropriate control signals are asserted).

On the next clock rise the data presented to DQ (or a subset for byte write operations, see Write Cycle Description table for details) inputs is latched into the device and the write is complete.

The data written during the Write operation is controlled by BWS (BWS[a:d] for CY7C1330AV25 and BWS[a:b] for CY7C1332AV25) signals. The CY7C1330AV25 and CY7C1332AV25 provide byte write capability that is described in the Write Cycle Description table. Asserting the Write Enable input (WE) with the selected Byte Write Select (BWS) input will selectively write to only the desired bytes. Bytes not selected during a byte write operation will remain unaltered. A Synchronous self-timed write mechanism has been provided to simplify the write operations. Byte write capability has been included in order to greatly simplify Read/Modify/Write sequences, which can be reduced to simple byte write opera- tions.

Because the CY7C1330AV25/CY7C1332AV25 is a common I/O device, data should not be driven into the device while the outputs are active. The Output Enable (OE) can be deasserted HIGH before presenting data to the DQ inputs. Doing so will tri-state the output drivers. As a safety precaution, DQ is automatically tri-stated during the data portion of a write cycle, regardless of the state of OE.

Power-up/Power-down Supply Voltage Sequencing

The power-up and power-down supply voltage application recommendations are as follows:

Power-up: VSS, VDD, VDDQ, VREF, VIN.

Power-down: VIN, VREF, VDDQ, VDD, VSS.

VDDQ can be applied/removed simultaneously with VDD as long as VDDQ does not exceed VDD by more than 0.5V.

Programmable Impedance

An external resistor, RQ, must be connected between the ZQ pin on the SRAM and VSS to allow the SRAM to adjust its output driver impedance. The value of RQ must be 5X the value of the intended line impedance driven by the SRAM, The allowable range of RQ to guarantee impedance matching with a tolerance of ±10% is between 175Ω and 350Ω, with VDDQ=1.5V. The output impedance is adjusted every 1024 cycles to adjust for drifts in supply voltage and temper- ature.The output buffers can also be programmed in a minimum impedance configuration by connecting ZQ to VDD.

Sleep Mode

The ZZ input pin is an asynchronous input. Asserting ZZ places the SRAM in a power conservation “sleep” mode. Two clock cycles are required to enter into or exit from this “sleep” mode. While in this mode, data integrity is guaranteed. Accesses pending when entering the “sleep” mode are not considered valid nor is the completion of the operation

Document No: 001-07844 Rev. *A Page 4 of 19

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