I'm trying to design an asynchronous counter with JK flip- flops, with an arbitrary sequence.

enter image description here

The sequence is: 0, 1, 2, 3, 4, 5, 2 ?

I know how to solve this kind of problems, but in this case how can one solve this problem with the 6 and 7 ? Because a state can only have one next state ?

Edit: This is what I did so far after doing the K maps. I get J2 = 0, K2 = Q1, J1 = 0, K1 = 0, J0 = 0, K0 = Q2Q1. But when I try to simulate it in multisim, it gets stuck to 0. Did I make a mistake in my k map simplifications or is there an issue my circuit ?

N.B. in this image, Q1 is the LSB, Q2 is the '2' bit, Q3 is '4'

  • \$\begingroup\$ is this a school assignment? .... how does it get to state 6 or state 7 ? \$\endgroup\$
    – jsotola
    Apr 7, 2018 at 20:25
  • \$\begingroup\$ yes, i have no idea how it can get to the state 6 or 7... \$\endgroup\$ Apr 7, 2018 at 20:50
  • \$\begingroup\$ Then you also have no idea how it can get to 0. \$\endgroup\$ Apr 8, 2018 at 0:42
  • \$\begingroup\$ Use a PROM to control the state machine. \$\endgroup\$ Apr 8, 2018 at 4:27
  • 1
    \$\begingroup\$ Voting to close as the problem behind this question simple isn't answerable until you have a complete specification. With what you have right now there are many approaches that could be taken, but each would rely on unvalidated assumptions as to what behavior is actually desired. Don't guess or ask us to - re-read the requirement, have a discussion with the stakeholders, or examine the application to more carefully determine the need. \$\endgroup\$ Apr 8, 2018 at 17:54

2 Answers 2


Design the state transitions for 6 and 7 as well (next state = anything but 6 or 7. 2 is OK.) Otherwise a glitch may cause your counter to lock up in an undefined state. Use the "else" case if your design environment allows it.


You have two conditions to consider:

  • Current state not > 4: next state is increment
  • Current state > 4: next state is go to 2

That works out to one logic op, an increment and a mux to select between the two next states.


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