Use a PIC ADC like a fast interrupt comparator?

[pxidr84]

Again... HOW MUCH LATENCY IS ACCEPTABLE?? Is 1nSec too much? is 1millisecond too much? Give us a number!

Few µs (1-10µs.)

[Charles Linquis]

I haven't tried it (yet), but I believe that if you run an 18F chip at 40Mhz, and write an ISR in ASM, you can probably get the latency down to about 25uSec.