Maybe an easier method would be to simply connect a dual optical isolator via resistor directly to the micro controller transformer on the secondary ac side. Your open collector outputs will switch at every zero crossing. That signal is connected to the hardware interrupt which services the routine....

See below

Did this get sorted?

Martin! Thank you... Happy New Year.

Using PIC18f27q10. FC11 I have two interrupts. One is a hardware input interrupt. The other is a timer0 interrupt. I believe that priorities are settable but requires a few c code register adjustments such as (maybe): IPR0bits.INT0IP = 1; // High priority IPR0bits.TMR0IP = 0; // Low priority I don't...

Thank you. I think I have selected the correct register number for the osc? Maybe not? I have attached my file

If the system timing is correct at 20mhz, would that not indicate internal oscillator to be correct?

Flowcode version 9.

Running a short program at project option speed 32 (mhz). Delay times are double expected time. I changed to project option time to 20 mhz and the delay times are correct.

FYI

I see -Thanks Chip! The selections in the interrupt component differentiate between IOC and Int0 so I think that selecting int0 should give me the individual action. However, selecting int0 allows all portA pins to run the interrupt macro. I suspect that FC sees no difference. Maybe it's flipped and...

Side note - The hardware actually performs the PWM. Side note 2 - Selection of the INTO pin seems not to apply just to the pin. Seems that all pins (IOC) are involved. Regardless of which pins are activated, the interrupt macro runs.