Cypress CY7C1294DV18, CY7C1292DV18 manual Dll

CY7C1292DV18

CY7C1294DV18

Byte Write Operations

Byte Write operations are supported by the CY7C1292DV18. A Write operation is initiated as described in the Write Opera- tions section above. The bytes that are written are determined by BWS0 and BWS1, which are sampled with each 18-bit data word. Asserting the appropriate Byte Write Select input during the data portion of a Write will allow the data being presented to be latched and written into the device. Deasserting the Byte Write Select input during the data portion of a write will allow the data stored in the device for that byte to remain unaltered. This feature can be used to simplify Read/Modify/Write opera- tions to a Byte Write operation.

Single Clock Mode

The CY7C1292DV18 can be used with a single clock that controls both the input and output registers. In this mode, the device will recognize only a single pair of input clocks (K and

K)that control both the input and output registers. This operation is identical to the operation if the device had zero skew between the K/K and C/C clocks. All timing parameters remain the same in this mode. To use this mode of operation, the user must tie C and C HIGH at power on. This function is a strap option and not alterable during device operation.

Concurrent Transactions

The Read and Write ports on the CY7C1292DV18 operate completely independently of one another. Since each port latches the address inputs on different clock edges, the user can Read or Write to any location, regardless of the trans- action on the other port. Also, reads and writes can be started in the same clock cycle. If the ports access the same location at the same time, the SRAM will deliver the most recent infor- mation associated with the specified address location. This includes forwarding data from a Write cycle that was initiated on the previous K clock rise.

Depth Expansion

The CY7C1292DV18 has a Port Select input for each port. This allows for easy depth expansion. Both Port Selects are sampled on the rising edge of the Positive Input Clock only (K). Each port select input can deselect the specified port. Deselecting a port will not affect the other port. All pending transactions (Read and Write) will be completed prior to the device being deselected.

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 ±15% is between 175Ω and 350Ω, with VDDQ = 1.5V.The output impedance is adjusted every 1024 cycles upon power-up to account for drifts in supply voltage and temperature.

Echo Clocks

Echo clocks are provided on the QDR-II to simplify data capture on high-speed systems. Two echo clocks are generated by the QDR-II. CQ is referenced with respect to C and CQ is referenced with respect to C. These are free-running clocks and are synchronized to the output clock (C/C) of the QDR-II. In the single clock mode, CQ is generated with respect to K and CQ is generated with respect to K. The timings for the echo clocks are shown in the AC Timing table.

DLL

These chips utilize a Delay Lock Loop (DLL) that is designed to function between 80 MHz and the specified maximum clock frequency. During power-up, when the DOFF is tied HIGH, the DLL gets locked after 1024 cycles of stable clock. The DLL can also be reset by slowing or stopping the input clock K and K for a minimum of 30 ns. However, it is not necessary for the DLL to be specifically reset in order to lock the DLL to the desired frequency. The DLL will automatically lock 1024 clock cycles after a stable clock is presented.the DLL may be disabled by applying ground to the DOFF pin. For information refer to the application note “DLL Considerations in QDRII/DDRII/QDRII+/DDRII+”.

Document #: 001-00350 Rev. *A Page 6 of 23

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