External Memory Interface Handbook Volume 2: Design Guidelines

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ID 683385
Date 5/08/2017
Public
Document Table of Contents

1.1.9. QDR II, QDR II+ and QDR II+ Xtreme SRAM Data, BWS, and QVLD Signals

QDR II, QDR II+ and QDR II+ Xtreme SRAM devices use two unidirectional data buses: one for writes (D) and one for reads (Q).

At the pin, the read data is edge-aligned with the CQ and CQ# clocks while the write data is center-aligned with the K and K# clocks (see the following figures).

Figure 3. Edge-aligned CQ and Q Relationship During QDR II+ SRAM Read


Figure 4. Center-aligned K and D Relationship During QDR II+ SRAM Write


The byte write select signal (BWS#) indicates which byte to write into the memory device.

QDR II+ and QDR II+ Xtreme SRAM devices also have a QVLD pin that indicates valid read data. The QVLD signal is edge-aligned with the echo clock and is asserted high for approximately half a clock cycle before data is output from memory.

Note: The Intel® FPGA external memory interface IP does not use the QVLD signal.

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