you misunderstoot my post. TIMER0 is what i want to use for this new function, i'm already using, or are planning
on using, TIMER1 and TIMER2

On Mon, 11 Jun 2001 13:04:37 -0400, Olin Lathrop wrote:

>I never got the original of this message for some reason.
>
>> >16F877 chip @ 4 Mhz
>> >
>> >i'm considering using the timers in a project .. what i'd like is an
>> >interrupt every .250 seconds
>> >
>> >i'm already using timer2 for PWM
>> >i'd *like* to use timer1 for a counter
>> >
>> >somebody check my math for me please :
>> >
>> >timer0 runs at 1 Mhz (Fosc/4) ..
>> >
>> >most prescale you can get is 256 ..
>> >
>> >8 bit counter ..
>> >
>> >
>> >working all this out, the *slowest* i can get timer0 to run (on my
>> >calculator) is .065536 seconds
>> >
>> >is this right ?
>
>No.  Timer 1 has a 3 bit prescaler (divide by 1, 2, 4, or 8), but is a 16
>bit counter.  You want an interrupt every 250,000 instructions.  With a
>prescaler of 4, you want an interrupt every 62,500 timer 1 increments, which
>is within its 16 bit range.  You can use the second CCP to automatically
>provide the period value, or you can interrupt on timer 1 overflow and then
>adjust timer 1 in the interrupt routine to "skip over" the extra 65536 -
>62500 = 3036 increments.
>
>
>********************************************************************
>Olin Lathrop, embedded systems consultant in Littleton Massachusetts
>(978) 742-9014, olin@embedinc.com, http://www.embedinc.com
>
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