User guide

14-5

Negative Timing Checks

Figure 14-3 Negative Setup Limit

Here the $setuphold timing check is in the specify block of the

top-level module of the cell. It specifies that there is a timing violation

if there is a data event between 10 and 31 time units after the

reference event on the cell boundary.

This is giving the reference event a “head start” at the cell boundary,

anticipating that the delays on the reference event will allow the data

events to “catch up” at the sequential device inside the cell.

Note:

When you specify a negative setup limit, its value must be less

than the hold limit.

setup

limit

hold

limit

violation window

reference

event

data

event

data

event

clock

data