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max PWM problem PIC18F4520

 
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max PWM problem PIC18F4520
PostPosted: Mon Jul 27, 2009 3:02 pm     Reply with quote
I cant seem to get a maximimum PWM output using timer2.

Theoretically I using a 4Mhz clock I should be able to get a 1Mhz PWM output. I have tested the following code and do not get any output from ccp1 or ccp2 in PWM mode. The does not work until a get preload a value of 50 or above.

I can't find any talk of a min preload or max pwm speeds relative to clock speed. Am i missing something here. What is the maximum PWM speed relative to clock that i can have?

PIC18F4520
compiler 4.083

Code:
#include <18F4520.h>
#fuses INTRC,MCLR
#fuses CCP2B3  //multiplex ccp2 to rb3
#use delay(clock=4000000)


//*********************************************************************
void main(){

set_tris_b(0x00);
set_tris_c(0x00);

setup_ccp1(CCP_PWM);
setup_ccp2(CCP_PWM);

setup_timer_2(T2_DIV_BY_1,0,1);//1mhz
//1/((4*1*(0+1)*1)/4Mhz) = 1 Mhz oscillation

set_pwm1_duty(50);//is this duty cycle or % time on!?
set_pwm2_duty(50);

while(1){

delay_ms(1);

}//while
}//main
PCM programmer



Joined: 06 Sep 2003
Posts: 21708

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PostPosted: Mon Jul 27, 2009 3:18 pm     Reply with quote
No, it's not a percentage.

See Ttelmah's post at the end of this thread, which shows how to
get the maximum PWM frequency:
http://www.ccsinfo.com/forum/viewtopic.php?p=99719
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