Decade counter goes down and not goes up

[julian403]

Hi, I want to do a decade counter which goes from 0 to 7. I used 3 FF (because 2^3=8) JK. I put every J and K input with a higth level. And a clock signal at first flip flop with the output at next flipflop 's clock input. But it goes form 7 to 0 and not from 0 to 7.



As you can see, I do not put an initial condition.

Why it count down?

Thanks.

 

[barry]

Here's what's happening. Assume all three Q outputs are zero-call them Q1,Q2,Q3 from left to right. On the first clock pulse, Q1 goes high, which will clock Q2 high. Q2 going high will clock Q3 high. So you've just counted from 000 to 111. On the next clock pulse, Q1 goes low==> 110. On the third pulse, Q1 goes high, clocking Q2 low==>101. And so on.

It may not be doing what you WANT it to do, but it's doing exactly what it's supposed to do.

Try this: Use the Qbar output to clock the next stage, not the Q output.

 

[julian403]

Thanks, but what realy happends it's at first times all output's are hight and it's start to count from 0 to 7 if we take the low voltages level as 1.

If you see when there are leds, the count is going up if we takes the low voltages levels as 1

 

[barry]

You've got it all wrong. Low voltage is zero, high voltage is 1. Read the data sheet for the 4511. Again, this circuit is doing exactly what it's supposed to.

 

[julian403]

But, then in the video i used diodes to see the FF's output and the proteus show the logic levels too and you will see that it start with all output at high levels

 

[barry]

But, then in the video i used diodes to see the FF's output and the proteus show the logic levels too and you will see that it start with all output at high levels

So? You didn't force an output level, so your simulator chose to make all outputs high. So? It STILL is operating as a down counter.

 

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Either do as barry suggests and use the Q#_bar outputs to do your clocking (driving the 4511 with the Q# outputs, OR just drive the 451 with the Q#_bar outputs instead of the Q# outputs.

Either way you don't use the same JK flip flop output to do both (count and ripple clock).