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AR# 2527

XC4000E: Clarification about the IOB diagram specified on the data book


Keywords: CE, IK, Tecik, Tecikd, nodelay, IOB

Urgency: Standard


Why are there two specs for Clock Enable to Clock
delay (Tecik) for the IOBs, one with delay added and the other
without delay added? How can this be possible if only the D
input of the flip flop can be set to either delay or nodelay
according the data book description of the IOB?


In the 4000 family the clock enable of any flip flop is modeled
as a controller of a 2 to 1 mux muxing either the D or the Q of
the input flip flop in the IOB.
In reality, the controller that sets the signal to either
delay or nodelay is on the output of this mux.
As a consequence, the delay/no-delay setting affects both
the data and the clock enable signal going to the input flip
flop of the IOB.

On the other hand, the 4000EX/XL/XV devices only have the
delay/nodelay mux on the D signal.
AR# 2527
Date Created 07/12/1997
Last Updated 01/12/2003
Status Archive
Type General Article