Hi Peter

The thing is that I can afford waiting while inside the interrupt. The problem is when the control is inside the interrupt it seems to acknowledge another interrupt, although it is that is what is causing the problem and is counting one ot two more than actual bursts (rings) received.

I have also tried to disable interrupt immediately after entering it only re-enable interrupt after the burst is complete and just befre RETI. Even then it is causing problem. Don't know what's the problem.

I also tried disconnecting phone line and then energizing opto with constant manual pulse (at LED side) and no burst. This caused interrupt and I wanted to count X counts in the interrupt by energizing the opto X times but, it always counts less than X.

Any solutions ??

Simon