Answers Database

Foundation Simulator: simulating bidirectional signals


Record #1286

Product Family:  Software

Product Line:  Aldec

Problem Title:
Foundation Simulator:  simulating bidirectional signals


Problem Description:
How do I setup simulation stimulus so that I can properly
simulate a bidirectional pin?


Solution 1:

Use the 'Chip Controlled' (CC) mode when simulating
bidirectional signals.	This will allow a chip (symbol)
output to override the test vector.

For example:

You are simulating a bidirectional pin BIDIR, and have
applied a stimulator to BIDIR.	You want this stimulus to
appear on BIDIR when the 3-state buffer is disabled.

Now, when the 3-state buffer is enabled, you want to view its
output on BIDIR, but the input test vector is overriding
the output.

Using CC mode on the BIDIR stimulator will allow the output
of the 3-state buffer to override the stimulus.

To apply the CC mode to a stimulator, select the signal in
the Waveform Viewer, and either click on the CC button in the
Stimulator Selection Window, or select Stimulator->Chip
Controlled Mode.

Stimulators that are in 'Override' (OV) mode are displayed
in red in the Waveform Viewer.	Stimulators that are in CC
mode are displayed in black.



Solution 2:

If using a CMD (script) file, use the 'release' command to
release the bidirectional pin.

IE:

h DATA	 #assigns input stimulus to bidi pin DATA
l EN	 #tri-states output enable
sim
h EN	 #enables output so that data is driven OUT onto DATA
r DATA	 #releases bidi pin DATA so that data may be driven out
sim



End of Record #1286