ModelSim SE User's Manual - Electrical and Computer Engineering

UM-266 9 - Waveform analysis
Using gating expressions to control triggering
ModelSim SE User’s Manual
Option Description
Strobe trigger Specify an interval at which you want to trigger data display
Trigger gating Use a gating expression to control triggering; see "Using
gating expressions to control triggering" (UM-266) for more
details
Trigger gating controls the display of data based on an expression. Triggering is enabled
once the gating expression evaluates to true. This setup behaves much like a hardware
signal analyzer that starts recording data on a specified setup of address bits and clock
edges.
Here are some points about gating expressions:
Gating expressions affect the display of data but not acquisition of the data.
The expression is evaluated when the List window would normally have displayed a row
of data (given the other trigger settings).
The duration determines for how long triggeri ng stays enabled after the gating expression
returns to false (0). The default of 0 duration will enable triggering only while the
expression is true (1). The duration is expressed in x number of default timescale units.
Gating is level-sensitive rather than edge-triggered.
Trigger gating example using the Expression Builder
This example shows how to create a gating expression with the ModelSim Expression
Builder. Here is the procedure:
1 Select Tools > Window Preferences to access the Triggers tab.