PIC16F88 and PWM

xavier · Joined: 10 Feb 2004 Posts: 7

Hello,
I'm trying to do PWM with a PIC16F88 and it's not working.
My example is very simple and I don't understand where i'm wrong.
With output_low and output _high pin B3 is working fine but not with PWM !
I'tried to compile it with v4.032 and v3.190 no change !
Can somebody show me the way ...please

The Code :

#include <16F88.h>
#fuses HS,NOWDT,NOPROTECT,NOLVP
#use delay(clock=20000000)
#use rs232(baud=115200,parity=N,xmit=PIN_B5,rcv=PIN_B2,bits=8,errors)

void main() {
byte value;

set_tris_b(0b11110111); // B3 Output
setup_ccp1(CCP_PWM);
setup_timer_2(T2_DIV_BY_4, 255, 1);
set_pwm1_duty(0); // PWM off

delay_ms(1000);
printf("Starting\n\r");

while( TRUE )
{
value++;
printf("%2X\r",value);
set_pwm1_duty(value);
delay_ms(100);
}
}

Many thanks in advance
Xavier

sandropiovesana · Joined: 06 May 2008 Posts: 9

I've fast read your code, my first idea is:

try to change:
setup_timer_2(T2_DIV_BY_4, 255, 1);

with:
setup_timer_2(T2_DIV_BY_4, 100, 1);

Good Luck

stewart · Joined: 28 Nov 2005 Posts: 12

xavier

PWM is super easy. It simply is based on 3 things: TMR2, CCPR1 and PR2

CCPR1 holds the period, at which point TMR2 is reset, and the output goes high. when TMR2 matches the value of PR2, the output is cleared.

Read the data sheet in this area, look-up the actual addresses of these registers and look at the listing file to see what these functions really do.

I can have a PWM running in less than 20 instructions in assembly, you have less than 4 statements to look at what they are doing in this C program.

DIVE INTO THE CODE IT HAS GENERATED

Dig a bit,

Stewart

PCM programmer · Joined: 06 Sep 2003 Posts: 21708

I stripped your program down somewhat by getting rid of all the printf
statements, and then I compiled it with vs. 4.074 and ran it on a
PicDem2-Plus board. It works. I see PWM output on pin B0.

xavier · Joined: 10 Feb 2004 Posts: 7

Many thanks PCM programmer for your help I found my pb ! (you mention RB0 in your post)

It was just because my scope was on RB3 instead of RB0 !!!
I'm so sorry i was sure pwm pin was RB3. (as i said on my first post)

Anyway all is working fine now ( since the beginning in fact ! )

Thanks again
Xavier