# need help in 12 hour format digital clock

Discussion in 'Homework Help' started by luckyveloso, Jan 21, 2010.

1. ### luckyveloso Thread Starter New Member

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badly need help in analyzing or implementing the circuit diagram of the hour part in 12 hour format clock using 74ls192 or 74ls90...tnx

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3. ### beenthere Retired Moderator

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How are you counting the seconds and minutes?

4. ### luckyveloso Thread Starter New Member

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the seconds and minute part goes well, it counts from 0 - 59...the only problem is the hour, coz it dont start at 01...instead it start from 00 then ended at 12, then back to 00...

5. ### beenthere Retired Moderator

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Use the parallel load function on the '192.

6. ### luckyveloso Thread Starter New Member

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can you explain the concept of the parallel load??? i gladly appreciate it...

7. ### beenthere Retired Moderator

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It's all on the data sheet. Every logic IC has one. It explains all the dunctions and how to make use of them. Google using "74ls192" as the search term.

8. ### Wendy Moderator

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Basically you can force the chip to start at the number of your choice.

9. ### sgardner025 Active Member

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With the 192 you could tie P0 high and P1-P3 low on the 1's place hour counter and tie P0-P4 low on the 10's place hour counter. Then you could use some decoding to take the PL inputs low during the next low to high clock transition on the 1's place hour counter.

10. ### luckyveloso Thread Starter New Member

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can you you show me the diagram or how you decode the PL inputs? i've been working this one for already a one week now and still i couldn't figure it out...pleaseee...thanks...

11. ### Wendy Moderator

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Use the LOAD as a reset, and the counter will go where you want. You might also take a look at the 4029, a very similar device. Pinouts are different, but it does exactly the same job.

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12. ### luckyveloso Thread Starter New Member

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i will try this one...tnx...^_^ i hope it works...

13. ### sgardner025 Active Member

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The PL inputs of the 74192 are active low so you need to take them from high to low whenever you want to load the counter. I attached an example where a binary 1 would give a low output. The msb would be at the top on the nor. You can use this method to decode the outputs of the counters. You just have to make it so that only the desired inputs give the output that you need.

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14. ### luckyveloso Thread Starter New Member

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i will try this one too...thank u very much by d way...i post again for upd8s...^_^