which method is useful and whats the diference in peformance of the two:- timer intrepputs or state machine
In some cases one is right and one is wrong, in other cases both are right, and some cases both are wrong.

Kinda like apples and oranges, they're different but both are good.
When they are the right choice. I have seen applications where either of the two were definitely the wrong choice.

programming (especially the '51) is not pantyhose, one size does not fit all.

Erik