On bigger programs it constrain the program flow dramatically, if CPU time was wasted by long delay routines.

Thus it is always a better approach to perform key debouncing and press detection inside a timer interrupt.

Especially since most programs need always a time base, then it is easy to insert the debouncing in this time base interrupt handler also.


My sample code:

http://www.8052.com/forum/read.phtml?id=57958

To add release detection, simple add this line:

<pre>
...
i &= ct0 & ct1; // count until roll over ?
// the following line must be added:
key_release |= key_state & i; // 1->0: key release detect
key_state ^= i; // then toggle debounced state
...


Peter