If this is for IR modulation (38Khz) you could even use the internal RC o=
sc?
But the frequency adjustment would be crude.
You could write a short loop with the 1uS instruction times and avoid usi=
ng=20
the Timer0?
Decrement a software timer 12 times and toggle a bit.
That would be the cheapest way using the internal RC osc.
PLUS you would not have to worry whether the Prescaler was set correct in=
=20
the Option Reg?

How accurate do you want?
38Khz is 26.3uS. So you want to set a bit high and back to low in that ti=
me?

For using a crystal and Timer0..
Use 16 MHz crystal  for 1/4 uS instruction cycle.  Prescale 2 and preload=
=20
Timer0 so timeout is in 26 cycles?   Preload would be (255-26).  That sho=
uld=20
be 13uS or half of the period.
Just be sure to read the rules on setting the prescaler and what happens =
to=20
it on PIC reset.
That is in the OPTION Reg, and on reset it get defaulted to a prescale of=
=20
128!
Put it back to 2 each time to be safe.  Read the warnings in section 4.4 =
of=20
the data sheet.

Have Fun!,

Mike Hagen
Crestline, Ca
Mike@DogItDesign.com
----- Original Message -----=20
From: "Octavio Nogueira" <nogueira@TATO.IND.BR>
To: <PICLIST@mitvma.mit.edu>
Sent: Wednesday, March 30, 2005 8:49 AM
Subject: [PIC]: generating 38KHz


>I need to generate 38KHz with 12F675 using TIMER0 or
> TIMER1 but I'm having some difficulties.
>
> I'm using external cristal and I can choose any
> commercial frequency.
>
> Any help to do this using MPASM?
>
> Octavio Nogueira
> Tato Equipamentos Eletr=F4nicos Ltda
> (11) 5506-5335
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> nogueira@tato.ind.br                  ICQ# 222558485
> BASIC Step - O microcontrolador mais f=E1cil do mercado
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