# Counter design with stopping

Joined Jun 8, 2020
1
Hello everyone, I designed a counter that counts 0,4,6,8,12,14. But I want it to stop when it shows 1110. As you can see at left bottom corner of the circuit, I put an "And" gate and I linked four outputs of flip flops to the gate as inputs. I thought that if I obtained "1", that would enough to reset the circuit. But this process resets the circuit before "1110". That is, it shows 1100(12) and goes off. What kind of correction or strategy do you recommend? Thanks in advance.

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#### MrChips

Joined Oct 2, 2009
24,618
But this process resets the circuit before "1110". That is, it shows 1100(12) and goes off.
The circuit does not reset at 1100. It resets at 1110.
In other words, the circuit reaches 1110 but you do not observe this because it only stays in that state for the duration of the gate propagation time.

What are the solutions?
1) You can cheat and decode for the next state beyond 1110. This is not a recommended solution.
2) Use a synchronous solution, one that changes only on the clock cycle, current state -> next state.
3) Delayed clock, for example, advance on leading clock transition, decode on trailing transition.
4) Delay the reset signal, i.e. accept the reset signal at a later time in the cycle.

#### WBahn

Joined Mar 31, 2012
26,398
How are we supposed to know what each of the pins on your FF are?

What do you mean by wanting it to stop? Do you want it to just continue showing 1110 from that point on?

If so, then what state should your counter go to if it is in state 1110?

#### dl324

Joined Mar 30, 2015
13,518
Welcome to AAC!

Because this is homework, and your schematic drawing style is unreadable, you need to post your work.

Two other students are working on a similar problem, but they're using JK flip flops and need to count in two different sequences. The other is binary, which drives the solution in a particular direction.

I can't tell what type of flip flop you're using (the 'O' isn't helpful. It also isn't easy to discern which flip flop is the most significant bit. You should label them and then tell us which letter is the LSB. It seems that schools are teaching it backwards. Since I started working with counters in the 70's, 'A' has always been the LSB, but students have been posting with 'A' as the MSB.

You can post your Logisim file if you change the extension.