thanks alot Pelt..
your replied really helped me starting ...
but according to your reply...there's a minor part which i dont really understand..

- If the low digit second count underflows, set it to 9, and decrement high second count.
- If high second count underflows, set it to 5, and decrement minutes. etc. for minutes and hours

how does mcu knows it's underflow?
i know that in mcu, when the timer count from FFH to 00H it will set the TFx bit to high...this is called overflow ..right?
when the timer count backward from 00H to FFH (possible??)...underflow??...
according to the tutorial section...the timer always count up...so it wont count backward..
can u elaborate more on this technique?..

sorry..my english is bad..