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Designing a synchronous counter 
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#1
May206, 04:55 AM

P: 1

Hi everyone. There are 2 questions i cannot solve here. So i am hoping someone here can help me out. Here are questions:
(1) Design a synchronous counter using JK flip flops which will count through the sequence 0, 2, 4, 6, 8, 10, 12, 14, 0. (2) Design a synchronous down counter using JK flip flops which counts backwards from 9 down to zero. 


#2
May206, 09:03 AM

PF Gold
P: 1,684

When designing a sync counter. You need to remember that the clock signal hits all the JK FF at once as opposed to a async counter (where the output of one FF is the clock for the other). Remember that all JK must be in toggle mode. We enable each JK flipflop to toggle based on whether or not all preceding flipflop outputs (Q) are "high." To do this we need AND Gates. Read this and then you may be able to build your counters. It also schematic diagrams for a few counters that you can reference.
One difference between the up and down counter, is the input thats fed into the AND Gate. For a up counter the Q input is fed into the AND Gate and for the down counter the Q(inverted) input is fed into the AND GAte. 


#3
Apr2511, 11:58 PM

P: 2

i'm trying to find out how to design a synchronous up/down counter using JK Flip Flops. Counting up in the sequence 1,3,5,7,4,2 and down count 2,4,7,5,3,1. Also i would like to know how the control input will be connected to the counter?...



#4
Apr2611, 01:21 AM

Sci Advisor
P: 2,751

Designing a synchronous counter
Start by making a table of : Input and PresentState versus NextState. This is called the state transition table.
Next you work out what values of J and K are required to make the above transitions. These truth tables (or kmaps) are called the flipflop excitation tables (maps). For optimal design don't restrict the JK flipflops to only toggle function but use the following assignments to determine your flipflop excitation.



#5
Apr2711, 04:28 AM

P: 2

Yeah...I've done all of that and got this.
Up counter>>.......Ja=C'+B Ka=BC Jb=A+C Kb=1 Jc=AB Kc=A' Down Counter>>...Ja=B'C Ka=B'C' Jb=1 Kb=A+C' Jc=A'B Kc=A'B+AB' Now I'm stuck on how to merge the up and down counter with the control input....please help!!! 


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