At 06:59 PM 8/9/01 -0000, you wrote:
>Dan,
>      On the 74AC74 [which is good to ~180 mhz,
>> IIRC], how far down can you count using the pre-scaler?  I was advised
>that many prescalers do not count down very low because of capacitance
>effects internal to the prescaler itself.
..........


The 74AC74 is just a flip-flop - I hooked up 2 stages to get /4.
This allowed me to count to 4x over what Timer1 could take directly.
The prescaler I was referring to is the one in the PIC, ahead of
Timer1. For commercial prescalers [external chips], you will have
to check the particular specs.

Most fast parts have a problem with slow input transitions - when
the slow signal is passing thru the threshold voltage, noise
riding on the signal will lead to false triggering, but you can
add hysteresis or use a schimt trigger part [eg, 74AC14] to deal
with this. If you want Mostly, I have been talking about counting
"digital" pulses. If you want your counter to deal with analog
signals, that is an entirely different breed of animal. [in
which case you might want to spend $99, and buy one off the
shelf].

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