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AR# 17293

7.1i CPLDFit - Using MAXPT to create logic buffers and control optimization

Description

Urgency: Low

General Description:

The CPLDFit software automatically collapses equations up to the limit set in the ISE software: Collapsing Product Term Limit.

This might result in some equations being collapsed that I do not want collapsed.

How can I control product term optimization for a specific equation instead of globally?

Solution

If you have an equation for which you wish to set the collapsing product term limit to a smaller value than the others, this can be done with a MAXPT constraint. This sets the collapsing product term limit to a specific equation.

Example usage:

A design has 12 outputs in a function block and due to product term limitations, the software automatically buffers one of these outputs. This results in one output having an additional level of logic delay. Instead of having the software automatically pick which output to buffer, you can set the MAXPT constraint on one (or more) of the other outputs to tell the CPLD software to buffer that equation instead. For more information on buffering, see (Xilinx Answer 12235).

NET myoutput MAXPT=1;

The above constraint would tell the CPLDFit software to do no collapsing on the equation 'myoutput'. Note that if 'myoutput' was 2 product terms to begin with, then CPLDFit will NOT break it up into two equations.

AR# 17293
Date Created 09/03/2007
Last Updated 12/15/2012
Status Active
Type General Article