I faced the problem while i make a digital clock.

Thread Starter

ricky0204

Joined Dec 9, 2020
2
I want to make a 24 mod using 74LS393
when clock reaches 24, it only resets 10 digit. ( I mean it changes 05, 06 ,07 after when it reaches 24)<< but i want to make it 00.
As you guys already know i want to reset 1 digit as well.. please help me and sorry for my broken english.
 

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andrewmm

Joined Feb 25, 2011
874
welcome back @ricky0204 ,
this is meant to do what ?
I guess you are not making this in real life as these parts are obsolete.

So this is home work.
Have you been told to use these counters ?
I ask as they are not synchronous, each output changes one after the other, not all at the same time.
check with a timing diagram what the output of your gates will look like in that condition.

You want to count 0 ,1, 2 ... 22,23,0,1,2..

so you need to decode the 23, and then reset the counter on the next clock edge,
 

Thread Starter

ricky0204

Joined Dec 9, 2020
2
welcome back @ricky0204 ,
this is meant to do what ?
I guess you are not making this in real life as these parts are obsolete.

So this is home work.
Have you been told to use these counters ?
I ask as they are not synchronous, each output changes one after the other, not all at the same time.
check with a timing diagram what the output of your gates will look like in that condition.

You want to count 0 ,1, 2 ... 22,23,0,1,2..

so you need to decode the 23, and then reset the counter on the next clock edge,
Thank you for answering.
I am making digital clock
I already made minutes and seconds..
so how to make a 24 counter using 74ls393? I have no idea.
 

MrChips

Joined Oct 2, 2009
22,468
74LS393 is a dual binary counter. You should use 74LS390 which is a dual BCD counter.

One counter counts tens, the second counter counts units.
You only need to decode two bits, QB from the tens and QC from the units.
Use this to reset the counters.
If this is for a digital clock you should not have to worry about the overflow glitch when decoding for 24 instead of 23.
 
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