Note that Timer2 is used in conjuction with the CCP
modules only for PWM.  Triggering a S/W interrupt on
match with the value in the CCPRxH & L requires the
use of Timer1.  (and Timer 3 in the case of the
PIC18F).

However, you could use the Timer2 interrupt.  That is,
figure out the prescale and postscale values and a PR2
value that gives roughly 50 ms.

For example, if the prescale is 1:256 and PR2 is 195
and the postscale is 1:1, this is 49.92 ms for a 4.0
MHz clock.  If you are using a 20 MHz clock, the
prescale might be 1:256, PR2 = 244 and the postscale
for 1:4.  (I am tired and may have made an error
here).

***********

There is a good deal of confusion caused by the use of
the names CCP1 and CCP2 and Timer1 and Timer2 which
might falsly lead one to believe that Timer1 is
associated with CCP1 and Timer2 with CCP2.  This is
not true.  However, the PR2 register is inherently
linked with Timer2.

**************

If you subcribe to my C routines distributions, see
routine TIMER2_1.C.

Hope this helps.

Peter H Anderson, http://www/phanderson.com,
pha(at)phanderson.com



--- cdb <bodgy1@OPTUSNET.COM.AU> wrote:
> I am trying to use timer2 on a 16F877 to create an
> interrupt roughly
> every 50mS.
>
> To this end I have enabled the software interrupt in
> CCP2CON to
> software trigger (0x0A), loaded CCPR2L with 'd' 30.
> T2CON I have
> postscale *16, PIE2 is enabled as is PIE in INTCON
> (I'm using TMR1
> elsewhere).
>
> The value for CCPR2L comes from CLOCK 10MHz /4=
> 1/(2.5MHz/256/16/30)=49.15mS
>
> My problem is that at 51mS the test for CCPI2 in
> PIR2 is set - no
> problem, however it will not clear until approx 58mS
> have passed and
> then does not set itself again.
>


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