Summary of info I gleaned from this thread...

PIC16F84 chips are good up to a max clock speed of 50-60 MHz (counting on
the RA4 schmitt trigger input)
74HCxx chips are good up to a max clock speed of 36 MHz
74Fxx chips are good up to a maximum of 100-125 MHz
ECL (emitter coupled logic) can get up to 2 GHz

As Peter onion pointed out, I made a simmple error in that a 0.1s count
period the bit 0 of the counter equates to 10Hz, so bit 7 equates to 2560
Hertz not KILO Hertz.

Thanks to all.

Ted Mawson
PICman@portfoliopm.com

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