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Thread: Generating a 120KHz pulse
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picon face BY : Drew Vassallo email (remove spam text)



>  Actually, you'd have to use 4.1 uS and 4.2 Us because the period is
>  8.333uS.  Your statement would put the period at 16.6 uS which would
>  be about 60Khz.  But if he can handle a slightly non symetrical wave
>  form, this would be a good idea.  The duty cycle works out to ~49%
>  with 8.1uS as the high time and 50.6% with 8.2uS as the high time.
>  Either way, it's very close.

Jim, you can't get 4.1us with 20MHz clock, as the cycle time is .200us.  If
you drop to 12MHz clock, you can get 0.33333333us per clock cycle, giving 25
instructions for 120KHz operation, but still can't be broken down into 2
equal pulses.  Even at 16MHz, you get .250us per cycle, or 33.33333333
instructions for 120KHz operation, which still doesn't work.
You may be able to get an off-speed crystal, but I haven't done the research
on that one.

Your best bet is going with my 8.4us period (4.2us each high and low) at
20MHz, which is only 0.8% error.

--Andrew
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