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AR# 42133

IODELAY - Why is there an insertion delay even when tap is set to 0 in behavioral simulation?


In 7 Series/Virtex-6/Spartan-6 IODELAY behavioral simulation, there is an insertion delay even when the tap is set to 0.

What is this delay? 

Why is it seen in behavioral simulation?


This delay models the IODELAY intrinsic component delay, which is the amount of delay through the IODELAY even with tap=0.

This delay is a behavioral model so that users do not overlook the real insertion delay. 

Normally, delays are not modeled in behavioral simulation, but the delay block is an exception because users expect the behavior to be the same as in real hardware, for example, intrinsic delay plus tap delay.

This delay was added to the model for the Virtex-6, Spartan-6, and newer architectures and not for older architectures.

The following table outlines the delay value in each device family.

Device Input Side Delay Output Side Delay
7-series IDELAYE2 = 600 ps ODELAYE2 = 600 ps
Virtex-6 IODELAYE1 = 144 ps IODELAYE1 = 144 ps
Spartan-6 IODELAY2 = 100 ps IODELAY2 = no initial delay modeled
Virtex-5 IODELAY = no initial delay modeled IODELAY = no initial delay modeled
Virtex-4 IDELAY = no initial delay modeled No output delay available





AR# 42133
Date Created 05/12/2011
Last Updated 10/30/2015
Status Active
Type General Article
  • Virtex-6
  • Virtex-7
  • Kintex-7
  • More
  • Artix-7
  • Spartan-6
  • Virtex-5
  • Virtex-4
  • Less