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I am designing a counter circuit that will perform the following function:

A sequential circuit with three flip-flips A, B and C and two inputs X and Y. If X=0 and Y=0, the counter remains in the same sate. If X=0 and Y=1, the circuit goes through the state transition from 000, 001, 010, 011,100,101, 110, 111, back to 000, and repeats. If X=1 and Y=0, the circuit goes through the state transition from 111, 110, 101, 100, 011, 010, 001, 000, back to 111, and repeats. If X=1 and Y=1, the counter reset to 000.

I'm a little confused about the two inputs 01 and 10, and how to account for the inputs to JK.


State Table

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  • \$\begingroup\$ You will need a clock somewhere, else the outputs will never be stable. \$\endgroup\$ – TEMLIB Apr 20 '15 at 19:57
  • \$\begingroup\$ This is just the State Table -- I don't think the clock needs to be included here. \$\endgroup\$ – wellington Apr 20 '15 at 20:10
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You've gotten a little confused, I think. Your red entries should be for Jc/Kc. For the higher order bits A and B, and the current state 000, they remain at zero, and you use the same JK logic as you did for XY = 00 or 11.

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  • \$\begingroup\$ Okay, that makes sense. So, for instance, when ABC (present state) are 001, and XY = 01, Ja/Ka = 0X, Jb/Kb = 1X and Jc/Kc = X1.. The thing to remember here then is to only set the FlipFlop that is changing -- others leave it alone or reset it. \$\endgroup\$ – wellington Apr 20 '15 at 20:21
  • \$\begingroup\$ Yes, but additionally, if you want to change a bit, you can either force it (set or reset, whichever is appropriate) or toggle it (J and K both 1), and keep in mind that you can use your don't-cares to simplify the number of terms you need to generate the input. \$\endgroup\$ – WhatRoughBeast Apr 20 '15 at 20:28
  • \$\begingroup\$ How can we determine which flip-flop will work best? \$\endgroup\$ – wellington Apr 21 '15 at 3:23
  • \$\begingroup\$ Sorry? What are the choices, and what is your metric for "best"? \$\endgroup\$ – WhatRoughBeast Apr 21 '15 at 3:24
  • \$\begingroup\$ Yes, I suppose I should have been a little more specific. We've covered the JK, T, and D flip-flops only. By best, I mean low cost - maximum functionality. And in the world of electronic components, low cost generally means lower performance. \$\endgroup\$ – wellington Apr 21 '15 at 15:14
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You are designing a synchronous 3-bit Up/Down counter using JK flip-flops.

http://www.electronics-tutorials.ws/counter/count_4.html shows and explains such a counter.

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