I'm no maths expert but I have come up with these eqations which might be
of assitance. I make no guarantees as to their accuracy... ie. they may be
wrong but I think they are right.

If:
t = time required (sec)
f = clock frequency of the PIC (Hz)
p = prescaler ie. 2, 4, ... 256
TMR0 = start value of TMR0

t = (256-TMR0)(4p/f)
TMR0 = 256-(tf/4p)
p = tf/(4(256-TMR0))

___________________________________________
Wesley Moore
RMIT - BEng/BApp.Sc. 2nd Year

wmoore@cs.rmit.edu.au
http://wmoore.tsx.org/

On Sun, 30 Jul 2000, Luis Fernando wrote:

>  Hi There,
>
>  Is there any universel equation that i can use to get the right
> prescalar that i need and the right number that i should put into the
> TMR0 so that it can get the right timing ???
>
>  Thanks
> R.C.
>
>
>  Hi,
> Yes I saw it on the Myke Predko's book.
> There are two way to get it...
>  If you want the delay..
>
>  Delay = (256 - InitTMR0 * prescaler)
>              -----------------------------------------
>                      Frequency / 4
>
>  Or if you want the value to put in TMR0 to get a determinate DELAY
>
>  InitTMR0 = 256 - ( DELAY * Frequency ) / ( 4* Prescaler)
> Ah! DELAY in seconds
>
>  I hope that I could help you
>
>  Regards
>  Luis F
>
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