Perhaps if you disabled the TMR1 and CCP modules, then reset the timer 1 and
CCPR1H:CCPR1L registers, and then reenabled both modules this odd behaviour
would disappear.

I am guessing that you are getting some kind of transient match condition
between the tmr and ccp regs that if triggering CCP1IF.

Bob Ammerman
RAm Systems


> Fwd on behalf of Dan Michaels
>
> Problem and solution here, DM would appreciate any
> insights
>
> ======================================
>
> I'm writing code to use a 16F873 to time 16 R/C servos:
>
> - 20 mhz xtal
>
> - using timer0 for epoch timing, 2 "polled" overflows w/prescale=256
>   and presetting to 244 gives 2*12.5 msec long epochs [works fine].
>
> - using timer 1, in compare mode with CCP1IF interrupts to time the
>   servo pulses, internal clock, prescale/1, generate s.w. interrupt
>   on match, CCPR1L = 0Ah.
>
> - with this setting, CCPR1H:CCPR1L values from 0-20000 give
>   0-4000 usec long pulsewidths.
>
> - I setup for 1st servo pulse, let the interrupt go, and stop timer1.
>   Then, back in the main programm, clear TMR1H:TMR1L, load
>   new values into CCPR1H:CCPR1L for the next servo, and re-
>   start timer1.
>
> The problem comes in as follows:
>
> - if I set CCPR1L != 00h with CCPR1H != 00h, everything is ok.
>
> - but if I set CCPR1L = 00h with CCPR1H != 00h, then the pulse
>   widths get crazy.
>
> - eg, CCPR1H:CCPR1L = 1301h --> 973 usec pulse, ok.
>       CCPR1H:CCPR1L = 1300h --> tiny pulse, few usec.
>
> I checked the Mchp errata sheets. It seems CCPR1L does
> not like a 00h.
>
> ===========================
> B4 I get a chance to fwd this problem to the list, Dan finds -
> ===========================
>
> Solution is:
>
> - when in compare mode for timer1, with TMR1 off ....
>
> - if I clear TMR1L and TMR1H registers "before" I set new values into
>   CCPR1L and CCPR1H, then I get the funny pulsewidth business.
>
> - but if I clear TMR1x "after" setting new values into CCPR1x, then
>   everything works fine. Botta bing.
>
> What gives?
>
> --
> http://www.piclist.com hint: The list server can filter out subtopics
> (like ads or off topics) for you. See http://www.piclist.com/#topics
>
>

--
http://www.piclist.com hint: The list server can filter out subtopics
(like ads or off topics) for you. See http://www.piclist.com/#topics