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I need help on a J K Flip Flop Counter

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angrypancake

New Member
Hey guys,

I have a final project which is a 12 hour clock counter. Now I've seen the forum threads about them and they go about the whole thing their own way. Now me being a student I'd actually like to learn rather than people giving me the answer. I have the minutes and seconds part of the clock done. That was easy but the hard part is the 12 hour. You can't use a 7490 because it doesn't have a preset. Which is what I wanted to use for the clock to go from 12 o'clock back to 1 o'clock. I want to clear the 1's clock at 10 which also clocks the 10's to 1. Which is 10 o'clock then have a NAND gate that will enable preset at 1 from 10's and 2 from 1's which is 12 o'clock that will enable preset which "SHOULD" set the 1's to a 1 instead of clearing it to 0. Now I can't find an IC chip that will do that. The 7493 only does BCD so 0-9 and thus not counting to 10.

My question is, is there any IC chips that counts like a 7490 but with a preset?

Now half of me decided that I'm just gonna build an asyncronous J-K Flip Flop Counter.

View attachment 63886

I started with that but my question with that is why the hell does it start the count at 6?
When I run the design it will do 6-9 clears at 10 then goes back to 0-9 and runs normally. I don't get why that happens. Can anyone explain? Am I doing something wrong? I need it to do 0-9 from the get go because I think when I add the 10's digit and the preset it just goes haywire and I can't try to troubleshoot a more complicated schematic when its already doing bad at the beginning.

I appreciate any help thanks!
 

ccurtis

Well-Known Member
I started with that but my question with that is why the hell does it start the count at 6?
Let me ask you a question. What makes you think it should not start the count at 6, or any other count for that matter? There is nothing there to determine what the count will be at power-up.
 

angrypancake

New Member
I was told that it should all be at 0 and nothing is clocking the higher significant bit. Determine what count will be at power up? I was never told of such a thing in class. Can you please expand on that?
 

ccurtis

Well-Known Member
Flip-flops can power-up in any state. There is no way to be sure what state they power up in, unless you reset/set them during or after power-up. How to do plan to set your clock after it powers-up? Since it obviously won't power-up to the correct time, it doesn't matter what count the clock starts at. It will be wrong, anyway.
 
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ccurtis

Well-Known Member
You can use a power-up reset circuit, like in the attached. It generates a pulse at power-up to reset devices with. But, whether it starts at zero, or 6, you still have to set the clock.
 

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ccurtis

Well-Known Member
This goes on the reset of the least significant bit or to all clrs? Also what do you mean you have to set it?
It goes on the clrs of each of the FFs you want to set to zero. By set, I mean set the clock.
 
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