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Simulating a Digital Circuit

With a complete schematic in the project, you can do a functional simulation of the digital circuit. This allows you to check the basic operation of the circuit so you can debug it before implementing it in hardware. This does not take into account lower level details.

Open the Logic Simulator by clicking on the Simulation icon in the main window.

In the Logic Simulator window, open the existing simulation state:

File $\to$ Load Simulation State...

and select andor.des. You should see the waveform of Figure 9.

  

Figure 9: Logic Simulator Window.

1.

The inputs A, B, C are mapped to the keys 'a', 'b', 'c' on your keyboard, and the logic values can be changed by toggling the keys.

2.

Set A to LOW by pressing the 'a' key when the mouse is focused in the Logic Simulator window. Observe the change in logic level.

3.

Click the Simulation Step button to continue the simulation for the next step (set to 100ns here). Observe the waveform.

The simulator uses a netlist generated from the schematic file. The existence of such a netlist is indicated by a tick (check) in the Design Entry icon. Netlists are also used for implementation. It is not hard to reset the simulation waveform - figure out how to do this and do it.

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