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ModelSim SE User's Manual - Electrical and Computer Engineering

ModelSim SE User's Manual - Electrical and Computer Engineering

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Tracing the source of an unknown (X)<br />

Tracing the source of an unknown (X) UM-307<br />

Another useful debugging option is locating the source of an unknown (X). Unknown<br />

values are most clearly seen in the Wave window—the waveform displays in red when a<br />

value is unknown.<br />

The procedure for tracing an unknown is as follows:<br />

1 Load your design.<br />

2 Log all signals in the design or any signals that may possibly contribute to the unknown<br />

value (log -r /* will log all signals in the design).<br />

3 Add signals to the Wave window or wave viewer pane, <strong>and</strong> run your design the desired<br />

length of time.<br />

4 Put a cursor on the time at which the signal value is unknown.<br />

5 Add the signal of interest to the Dataflow window, making sure the signal is selected.<br />

6 Select Trace > TraceX, Trace > TraceX Delay, Trace > ChaseX, or Trace > ChaseX<br />

Delay.<br />

<strong>ModelSim</strong> <strong>SE</strong> User’s <strong>Manual</strong>

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