External Memory Interface Handbook Volume 3: Reference Material

ID 683841
Date 7/24/2019
Document Table of Contents

1.17.4. Stage 1: Read Calibration Part One—DQS Enable Calibration and DQ/DQS Centering

Read calibration occurs in two parts. Part one is DQS enable calibration with DQ/DQS centering, which happens during stage 1 of the overall calibration process; part two is read latency minimization, which happens during stage 4 of the overall calibration process.

The objectives of DQS enable calibration and DQ/DQS centering are as follows:

  • To calculate when the read data is received after a read command is issued to setup the Data Valid Prediction FIFO (VFIFO) cycle
  • To align the input data (DQ) with respect to the clock (DQS) to maximize the read margins (DDR2 and DDR3 only)

DQS enable calibration and DQ/DQS centering consists of the following actions:

  • Guaranteed Write
  • DQS Enable Calibration
  • DQ/DQS Centering

The following figure illustrates the components in the read data path that the sequencer calibrates in this stage. (The round knobs in the figure represent configurable hardware over which the sequencer has control.)

Figure 24. Read Data Path Calibration Model

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