Bryce Reeve wrote:

>I have started programming a 20 MHz 16f877 chip (using Hi-Tech C).  I
>wish to have an interrupt formed every 1ms.  So I have Timer 1
>generating an interrupt.  However the by preloading the timer I can
>get an interrupt happening every 985s, if I the loading value.  The
>next step I get is a period of 1037us.  Surely I should be able to get
>closer to 1ms than this?
>
..........
> TMR1IE = 1;            // interrupt on overflow
> TMR1IF = 0;            // clear flag to start with
..........
>Any suggestions on where I might be able to improve the code to get a
>1ms interrupt happening that I can rely on?  I am relatively new to C
>and brand new to PICs so all comments are apprieciated.
>


With Timer1, try using the "special event trigger" interrupt mode
- selected by CCP1CON = xxxx1011. This way you initialize Timer1
once, and the value acts as the interrupt "period".

I assume '87x work the same as older '7x chips.

best regards,
- Dan Michaels
Oricom Technologies
http://www.sni.net/~oricom
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