gnupic: CCP in compare mode problem with PIC16F877
Subject:
CCP in compare mode problem with PIC16F877
From:
massimiliano ruggeri ####@####.####
Date:
8 May 2002 09:16:01 -0000
Message-Id: <3CD8EA12.3EAD7E44@cemoter.bo.cnr.it>
Hi All,
I have a question related to CCP modules in PIC 16F877.
There is someone that use CCP modules in compare mode?
I have tried to use CCP1 and CCP2 in compare mode, using
TIMER1.
My problem is to generate a PWM with a low period,
impossible to reach using PWM mode and prescaler, also with a 4 MHz
clock (and also I have a 5 K flash program, and dynamics at 1ms, then I
would
use a 20 MHz clock!!!).
The frequency would be approximately 100 Hz or less.
Then, fantastic compare mode feature, perfect for me!
My problem is that if I set RC2/CCP1 = 1 and RC1/CCP2 = 1, when TIMER 1
goes in overflow,
after this I try to reset CCP1 pin and CCP2 pin when TIMER1 match
respectively with
(CCPR1H and CCPR1L) and (CCPR2H and CCPR2L) using compare mode feature,
following the PIC16F877 manual.
OK, I'm sure that:
CCP1 and CCP2 are output (TRISC is OK).
but:
CCP1CON and CCP2CON are = 0x09 then (1001 - reset pin on match)
but the pin is always 0.
Note that if I use CCPxCON = 0x0A (1010 - generate interrupt on match
and pin remain
unchanged), and if I add in the interrput management procedure:
if (CCP1IF)
{
CCP1IF = 0;
RC2 = 0;
}
if (CCP2IF)
{
CCP2IF = 0;
RC1 = 0;
}
then it runs, the pins switch high and low!!!!!
No other changes in my code!!!!
Then the match is OK and also the interrpt is OK, then the module it
runs.
But in this way I will use 2 interrupt more than in the previous way,
using CCPxCON = 0x09 .........
I tried also the opposite way: set pin on match and reset the pin when
TIMER1 goes in
overflow (inside an interrupt procedure), with CCPxCON = 0x08 set output
on match.
There is something that I don't know about CCP?
I've read the 16F877 manual (only 1 page for CCP) and the AN594 from
microchip site, but this don't
helped me.
Someone can help me?
Thank you very much in advance.
Max
P.S. I have some problem in receiving the messages from the list in
these last days......
--------------
Massimiliano Ruggeri
CEMOTER - C.N.R.
National Research Council Of Italy
Fluid Power Group
www.cemoter.bo.cnr.it
