# Simulating a circuit?

Discussion in 'Homework Help' started by TripleDeuce, Oct 5, 2010.

1. ### TripleDeuce Thread Starter New Member

Sep 20, 2010
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I'm doing my prelab and it tells me
The function is given as F=(A'B) + (BCD'). I drew this out and then it asked me to use NAND-NAND realization for the function. So I made the AND gates NANDs and the OR gate a NAND as well and have this as my expression

F=((AB)'(BCD)')'

I made a truth table for the whole thing already as well. I just don't know how to draw the waveforms. We never really touched on this topic in class. Is there a software I could use to draw them?

2. ### Georacer Moderator

Nov 25, 2009
5,151
1,266
There is but I think it would be too complicated at this point to describe the circuit in HDL (Hardware Description Language) and simulate it. I guess it is better to do it by hand or line by line on the computer.

The key to this exercise is the following: You change your input every 100ns. But the gates have a delay of 10ns each. The circuit incorporates two levels of gates, the first NANDs that multiply the inputs and another NAND that multiplies the previous result. Total delay=(you can find that yourself).

So plot the input signals A,B,C,D and change them appropriately when needed. For example D will change every 100ns. Also draw F but it will change a specific time after each input change, time which is equal to the total delay you found earlier.

Don't overlay the plots, it will make a mess. Rather draw them one under the other with the time axis aligned.

3. ### TripleDeuce Thread Starter New Member

Sep 20, 2010
26
0
Would I need 16 of these graphs for every possible combination?

4. ### Georacer Moderator

Nov 25, 2009
5,151
1,266
Take a look at these pictures to get an idea of what you have to do.