Forum Discussion

Altera_Forum's avatar
Altera_Forum
Icon for Honored Contributor rankHonored Contributor
11 years ago

spikes in modelsim

Hi all, When simulating a basic counter (74161) I get spikes in modelsim – but I am unable to zoom in on those spikes in the wave window – see attachment. When analyzing the signals I se...
Altera_Forum's avatar
Altera_Forum
Icon for Honored Contributor rankHonored Contributor
11 years ago

The spikes are normal. The are likely an artifact of wait-statements, eg., "wait for 0 ns".

Modelsim has a list window that shows you a text version of the wave window, you could probably look at that if you really wanted to know more.

The main thing to take away from the display is that the signal with glitches is a *combinatorial* signal. Depending on what your design does with that signal, using it as a combinatorial input might be fine, other times you might need to register it, and use the register output.

Cheers,

Dave