Hi Simon,

yes, the flag was cleared on entering the interrupt.
But if you get a 2. transition during this interrupt, it was set again and cleared only by the next interrupt or you must clear it before RETI.

Seems, your ring signal differ from this in Germany.
If you get only 2 pulses your solution works.
If I get all 25 periods of the 25Hz signal in Germany my solution works.

Nevertheless I suggest to use a timer to detect, if the ring was finished. So you can reset the ring counter to be ready for the next call.


Peter