I have made this asynchronous counter (must be asynchronous) that using J/K flip flops that has to count from 2 to 9 and then reset to 2 and so on. I have managed to get it to count from 0 to 9, but I now have not been able to get it to start on 2. Please help!!enter image description here

  • \$\begingroup\$ Did you search the site here? I think I already solved this one -- or else one so close to it as to be a very near miss. Ah. It's this 9 downto 0 counter. Not the same thing. But the approach will work. \$\endgroup\$
    – jonk
    Apr 6 '21 at 2:55
  • \$\begingroup\$ Also this 0 upto 6 example may also help some. The first one I listed in the earlier comment shows you how to start things at any starting number you want. This 2nd one shows you how to more broadly approach the problem, including using J/K FF. If you can tell me what you do NOT understand from those, I may try to help. \$\endgroup\$
    – jonk
    Apr 6 '21 at 3:01
  • \$\begingroup\$ Maybe we are using different terminologies but how can you do an async (usually ripple) counter with a J-K flop which is by definition a sync element? \$\endgroup\$ Apr 6 '21 at 6:37

If you know how to use Clear inputs I can't find a reason why you are not able to use the Preset inputs? The change to make is too simple you just need to see it.

By the way, how did you make sure that this is a 0 to 9 counter?

  • \$\begingroup\$ I made sure by simulating it. And as to the clear, I have tried to connect the second ff to power and the others to ground but it didn't work, the display just stayed at 0. \$\endgroup\$
    – elmucho
    Apr 6 '21 at 2:53
  • \$\begingroup\$ The other must be connected to Vcc not to the ground since it is an activated low input. \$\endgroup\$ Apr 6 '21 at 3:00
  • \$\begingroup\$ But still my note concerning how did you make sure valid. In fact the first and last states (0 or 2 and 9) will last a half cycle, however the other states will last a full cycle and this is a bad design. Why don't you set the initial state at 10 asynchronously not at nine? \$\endgroup\$ Apr 6 '21 at 3:03
  • \$\begingroup\$ I connected the second ff to ground and the rest to VCC and now it just goes from 2 to 3 again and again \$\endgroup\$
    – elmucho
    Apr 6 '21 at 3:15
  • \$\begingroup\$ The preset of the second must be connected when it arrives at the last state all along with the clear inputs of other flipflops. \$\endgroup\$ Apr 6 '21 at 3:17

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