Hi Charles

Its not the noise problem, the signal is clean and the irratic behaviour was same and consistent always. Noise shows in the shape of inconsistant behaviour of the micro.


Hi Peter

The ISR-2 in my previous posting is working actually also. Clearing the flag before RETI worked. But why is it that we have to clear the interrupt flag of edge type in software, whereas the edge type interrupt flag is cleared by micro itself.


regarding why I am getting less counts is probably the ring pulse in my area has short pause in the burst. I mean the apparent one burst is in fact two closely spaced bursts, (one burst is made of two bursts with short gap between them) and after every two such bursts there is a long duration gap.

I think my analysis is right because I always get the count divided by 2.

Either I should increase the delay value or just double the counter value. To get X rings, the counter should count upt 2X.




Simon