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SGH

Wed Mar 28 2007, 10:02PM

Registered Member #672

Joined: Tue Mar 06 2007, 10:47PM

Posts: 38
Thanked 3 times in 3 posts

Hi all, I'm newbie in microcontroller and try to write a code for 4 digit count down counter with AT89S51.

Here are portion of the code.

count_down:
mov a,count1
dec a
mov count1,a
cjne a,#-1,exit_count
mov count1,#9
mov a,count2
dec a
mov count2,a
cjne a,#-1,exit_count
mov count2,#9
mov a,count3
dec a
mov count3,a
cjne a,#-1,exit_count
mov count3,#9
mov a,count4
dec a
mov count4,a
cjne a,#-1,exit_count
mov count4,#0

exit_count:
ret

The problem were if I put in following value, count1 = 0, count2 = 0, count3 = 1 and count4 = 0, it dosn't display correctly as everytime the 'dec' command was execute it fill in number 9 to previous count varible.

How to fix this problem ?. One more thing, at the end of count down, it doesn't display 0000, instead it display 9990.

Thanks all.
SGH

Ajay

Thu Mar 29 2007, 05:17AM

Rickey's World Admin

Registered Member #1

Joined: Fri Feb 24 2006, 04:56AM

Posts: 3753
Thanked 696 times in 655 posts

Well making a down counter is little tricky, i mean.. its not like simple decrement you need to check and wait till all zero and then exit.
cjne a,#-1,exit_count
mov count1,#9

this will surely make count 1 = 9 coz, after you dec count1 it will become -1 from 0. so according to statement, cjne(compare and jump if not equal) it will exit only if its not equal, but here its equal so, it will execute the next statement, so 9 is loaded in count1. so u are getting that result.

I made a program, but i want you to try it first, so giving you hint, you need to decrement the last digit, untill it become zero and when it become zero decrement the second digit, keep on doing this, utill u end up with all zeros!
i hope you got some idea, how to implement it, there are lot of compare jumps to be made i think, try it, if you don't get result, i will help you

www.rickeyworld.info
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SGH

Thu Mar 29 2007, 07:12PM

Registered Member #672

Joined: Tue Mar 06 2007, 10:47PM

Posts: 38
Thanked 3 times in 3 posts

Rickey, thanks for the hint. I'll try to rewrite the code.

SGH

Sat Apr 21 2007, 08:56AM

Registered Member #672

Joined: Tue Mar 06 2007, 10:47PM

Posts: 38
Thanked 3 times in 3 posts

I'm still trying to rewrite the code. I solved one problem but create another problem in the code.

So my progress in this code is slow. It is ok for me as this is part of the learning process.

SGH

learning process sgh rewrite