I got school project and I was trying to make counter that will count in this order: 1,3,6,5,2,4 and again but there is forbidden numbers 0,7(I assign 7 to 3 and 0 to 1 see border on table). So I used 3 JK flip-flops(C, B and A). There is table for counter:

Counter Table

After minimization I get following results:

Jc = B      Jb=A       Ja=~B+C 
Kc = A      Kb=~A      Ka=C~B+~C+B (XOR C+B)

And when I get it all together in Multisim (clock input of all JK FFs merged all together and connect to the CLOCK_VOLTAGE and 3 PROBE_DIG_RED to 3 ~Q outputs to see if it works) it just lights first two and turns off.

I also did another version in different sequence( to count up from 1 to 6 but not to show 0 and 7) and it displays 1,2,3,4,5,6 but in strage way. I was using 7 SEGMENT display and it shows me numbers 1,5,3,6 if I connect decoder to Qs of Flip flops but if I connect to ~Qs of FFs it shows 6,2,4,1. Is this how it works in Multisim or I have done something wronig ?

And what I have done wrong in current version of counter ?


1 Answer 1


So my first thought is it build out the un-simplified version, to ensure that your logic is correct. I know when I was in digital circuits I typically would do that and it would work, which would show an error in the simplification. If that is the case, slowly replace items until something doesn't work, then you have found it. If you build it unsimplified and it doesn't work, then it may in fact be an issue with how you set up your karnaugh map.

Again, the whole deal is process of elimination. If you have access to another simulator maybe build it there if you are confident, but I bet it is one of the above problems. At first glance it looks good, at least all of your don't care simplifications.


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