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=3D
1/(2.5MHz/256/16/30)=3D49.15mS

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.

 I am writing this program in 'C' but have changed the test from=
 the
torturous movlw 254 andwf H'0D' produced by the compiler to=
 inline
assembler BCF PIR2, CCP2IF but it makes no difference.

I have tried prescaling instead of postscaling but my=
 understanding
is that the S/W interrupt is generated after the postscalar for
timer2.

I have read the 16F8xx and 877 and AN594b pdf's but they all seem=
 to
leave me hanging, as they only describe in detail the PWM=
 attributes
of timer2.

I have seen this technique used by Peter Anderson using the CCS
compiler, so I assume it should work. Note my compiler is not=
 CCS.

My Timer0 and Timer1 routines work fine. Am I trying to use=
 timer2 in
a way it's not designed to be used?

Thanks for any help

Colin
--
cdb, cdb@barnard.name on 31/03/2002

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