Here is my whole diagram. There is no output while also clock is ticking...

I think there is a problem with the counter, but I can't figure it out.

I use rising-edge flipflops.

whole thing while clock= 0

whole thing while clock= 1

counter= 0

counter= 1

decoder= 0/1

  • \$\begingroup\$ I hope you will add your schematic soon. \$\endgroup\$ Jul 27, 2022 at 19:29
  • 2
    \$\begingroup\$ Since this looks like homework we will expect you to show us that you have made a substantial effort to solve this yourself. Show us all of your work: truth tables, state tables, etc. Describe exactly what "doesn't work" means. Then you can ask a specific question. \$\endgroup\$ Jul 27, 2022 at 20:06
  • \$\begingroup\$ You proably need a power-on reset to set the flip-flops to a known initial state. \$\endgroup\$ Jul 27, 2022 at 20:12
  • 1
    \$\begingroup\$ I added clock in place but no outputs. - Do you see the clock changing? \$\endgroup\$
    – Eugene Sh.
    Jul 27, 2022 at 20:15
  • \$\begingroup\$ Also your NAND output connection doesn't look good. Delete the line and reconnect. \$\endgroup\$
    – Eugene Sh.
    Jul 27, 2022 at 20:17

1 Answer 1


If those are positive edge triggered flip-flops then you need to come off the Q-bar outputs into the next clock inputs for an up counter. Come off the Q outputs as shown in your diagram if the flip-flops are negative edge triggered. If the flip-flops shown are positive edge triggered then the counter will count down from 0 direct to 15 and immediately reset back to 0.


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