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Thread: Crystal reccomendation
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face BY : Dan Michaels email (remove spam text)



Mike Harrison wrote:
.........
>>4) I realized I could use the OSC_OUT (At CLK/4) as a deglitch
>>   clock for a BiPhase-L output that got added at the last minute!
>OSCOUT will be the same as the input frequency - it's only fosc/4 in
>RC mode.
>It might be possible to get the PWM or compare output to run at Fosc -
>can't remember.
>

By using the 2 LSBs of the 10-bit PWM, you can get pulses out that
are only a quarter cycle long. With a 20 Mhz xtal, I use this technique
to generate 50 nsec pulses at a 5Mhz rate. Since the PR2 register
is totally programmable, you are not locked into only a few
PWM frequencies. You would set PR2 = 00h, IIRC, to get this rate.

Can also get 100/175/... nsec:

-___-___ or --__--__ or ---_---_

50ns        100ns       175ns     <-- pulse width

The center one will be 50% duty cycle at 5 Mhz even. You cannot get
the period < 200 nsec ~ 1/5Mhz for 20Mhz xtal.

- danM

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