External Memory Interface Handbook Volume 2: Design Guidelines

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ID 683385
Date 5/08/2017
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7.3.4.3.2. Board Skew Parameters for QDR II and QDR II+

The following table lists board skew parameters for QDR II and QDR II+ interfaces.
Table 80.  Parameter Descriptions

Parameter

Description

Maximum delay difference between devices

The maximum delay difference of data signals between devices is expressed by the following equation:

For example, in a two-device configuration there is greater propagation delay for data signals going to and returning from the furthest device relative to the nearest device. This parameter is applicable for depth expansion. Set the value to 0 for non-depth expansion design.

Maximum skew within write data group (ie, K group)

The maximum skew between D and BWS signals referenced by a common K signal.

Maximum skew within read data group (ie, CQ group)

The maximum skew between Q signals referenced by a common CQ signal.

Maximum skew between CQ groups

The maximum skew between CQ signals of different read data groups. Set the value to 0 for non-depth expansion designs.

Maximum skew within address/command bus

The maximum skew between the address/command signals.

Average delay difference between address/command and K

A value equal to the average of the longest and smallest address/command signal delay values, minus the delay of the K signal. The value can be positive or negative.

The average delay difference between the address and command and K is expressed by the following equation:

where n is the number of K clocks.

Average delay difference between write data signals and K

A value equal to the average of the longest and smallest write data signal delay values, minus the delay of the K signal. Write data signals include the D and BWS signals. The value can be positive or negative.

The average delay difference between D and K is expressed by the following equation:

where n is the number of DQS groups.

Average delay difference between read data signals and CQ

A value equal to the average of the longest and smallest read data signal delay values, minus the delay of the CQ signal. The value can be positive or negative.

The average delay difference between Q and CQ is expressed by the following equation:

where n is the number of CQ groups.

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