# 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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0
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
5,142
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
5,142
1,266
Take a look at these pictures to get an idea of what you have to do.
http://www.google.gr/imgres?imgurl=...&ndsp=28&ved=1t:429,r:7,s:41&biw=1680&bih=868
http://www.google.gr/imgres?imgurl=...3JBw&esq=1&page=1&ndsp=41&ved=1t:429,r:16,s:0
(Wow, huge links!)

I 'm afraid you will have to cycle through all 16 combinations. Dedicate 1 line for each input and output. Every vertical imaginary line is one time moment, so you will have to synchronize your inputs so that they go through all the combinations as time goes by.

Don't forget to add time delay to the output!

Post your graph for us to comment it.