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AR# 10639

12.1 Timing - How are External Setup and Hold times calculated?

Description

How are External Setup and Hold times calculated?

Solution

The calculation for External Setup time for pad-to-register paths:

Tsu(ext) = T(data_path) + Tsu(int) - T(clock_path)
T(data_path) = maximum data path delay
Tsu(int) = setup time of an internal register
T(clock_path) = minimum clock path delay

The calculation for the external Hold time for pad-to-register paths:

Th(ext) = T(clock_path) + Th(int) - T(data_path)
T(data_path) = minimum data path delay
Th(int) = hold time of an internal register
T(clock_path) = maximum clock path delay
An example of the External Setup and Hold times is illustrated in the following figure:

Figure 1 - Example Setup & Hold Times
Figure 1 - Example Setup & Hold Times

For more details on timing constraints, please see the Timing Constraints User Guide: http://www.xilinx.com/support/documentation/sw_manuals/xilinx12_1/ug612.pdf

AR# 10639
Date Created 08/29/2007
Last Updated 12/15/2012
Status Active
Type General Article