[HELP] 74ls193 count up and down as BCD

Thread Starter

FarProd

Joined Feb 9, 2012
10
I'm having problem designing 74ls193 count up and down as BCD from 00 to 99
(2 digits)

Using switch will interchange from up to down...

Any help out there....

I'm stuck!!!
 

Thread Starter

FarProd

Joined Feb 9, 2012
10
My goal is to use 74ls193 as counter and design BCD up and down counter from 00 - 99 vice versa (2 digits).

I figured out how 74ls193 work as BCD counter, but the problem is, when it count down, from 9 - 0.. it doesn't come back to 9.. it stay at 0 all the time.
 

SgtWookie

Joined Jul 17, 2007
22,210
You need to add logic so that when the output is zero, and the Down input is clocked, that 9 is loaded into the counter instead of 15 like is happening now; as soon as the count goes to 15, the AND gate loads in all zeroes.
 

Wendy

Joined Mar 24, 2008
21,906
You could go about this two ways. Draw a truth table that with any number over 9 it stuffs 9 into the preset.

Sense the binary number 10 (1010) and if the output is a 10 stuff 9 into the preset.

You say you must use a 74193, is this homework?
 

Thread Starter

FarProd

Joined Feb 9, 2012
10
No, I'm just experimenting.

I had just watched some videos of this using 74ls193, so i'm curious how they implemented it.
 

Wendy

Joined Mar 24, 2008
21,906
As has been said, the 74192 does it directly.

Have you tried coming up with the gate logic I described?
 
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Thread Starter

FarProd

Joined Feb 9, 2012
10
My only problem in my design is that., when it countdown from 9 and reached 0, after that it resumes to 1010 and detect (1010) that will lead to reset... so the output will be 0.

I know that 74ls192 would do it directly, but how about 74ls193?
 

Wendy

Joined Mar 24, 2008
21,906
Yes, the outputs will go to zero with reset. If you are counting down however the outputs will go to 1111. If the timer hits this condition you will need to stuff 1010 into the presets, and then toggle them in. I designed such a circuit a long while back. I used two different RC constants to sent a toggle after I sent the clock.

Interestingly, with that scheme (which I did breadboard, it is tested) the equivalent to 1010 was directly on the preset pins, no gates, just hardwired. Think of it as an alternate reset.

The reason I had to do it is it was a stadium counter, starting from either 3 or 2 on the countdown, with the standard 0 to 5 on the other digit.

Do you want to see it? It was rather a kludge, but it worked.
 

bertus

Joined Apr 5, 2008
20,102
Hello,

The problem is, when counting down, the counter will jump to 15 after it has gone through 0.
(see timing diagram)



You must detect the "15" and load a 9 at the monent it occurs.

I also have attached the complete datasheet.

Bertus
 

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Wendy

Joined Mar 24, 2008
21,906
Looking at it, you still have open inputs. This is a bad habit, which you really need to work on. Any true digital will be erratic and unpredictable, with the exception of TTL, which always assumes a high.

When I see this I go no further, as the schematic is incomplete. I suspect I am not the only one.
 

noblewolf

Joined Aug 14, 2007
1
My only problem in my design is that., when it countdown from 9 and reached 0, after that it resumes to 1010 and detect (1010) that will lead to reset... so the output will be 0.

I know that 74ls192 would do it directly, but how about 74ls193?
Hi,

If you are counting down (9..0): the "borrow" (pin 13) goes low in the transition from 0 to 15. Read this pin and when it goes low put 9 (1001) in the data pins (pins 1,9,10,15) AND set low the pin "load" (pin 11).

Hope this help.
 
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