Dear Graham,
thank you very much for your reply.
Yes, of course it was! I still have to study it further but I got the core idea. though I'm still questioning the necessity of debouncing for matrix keypads for normal applications your codes are very inspiring for me. in one occasion I wrote a routine for fast 16 bit to bcd conversion inspired by your Fast 32-bit Binary to BCD convertion routine.

thank you very much indeed