7 Capture Compare PWM

8/10/2019 7 Capture Compare PWM

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CAPTURE/COMPARE/PWMMODULES

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CCP Modules

• CCP : Capture/Compare/PWM .• Allows the user to time and control different events.

• Capture Mode, allows timing for the duration of an event

(TMR1 register).

• Compare Mode compares values contained in tworegisters at some point. One of them is the timer TMR1

register. Allows the user to trigger an external event

when a predetermined amount of time has expired.

• PWM - Pulse Width Modulation can generate signals ofvarying frequency and duty cycle.

• Two modules - CCP1 and CCP2.

• The Enhanced PWM features available on CCP1 only



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Capture Mode

In Capture mode, CCPR1H:CCPR1L captures the

16-bit value of the TMR1 register when an event occurs

on pin RC2/CCP1. An event is defined as one of the

following:• Every falling edge

• Every rising edge

• Every 4th rising edge

• Every 16th rising edge

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Capture a positive pulse

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#include <16F877.h>

#fuses XT, NOWDT, NOPROTECT, PUT, BROWNOUT, NOLVP

#use delay(clock=4000000)

#use rs232(baud=9600, xmit=PIN_C6, rcv=PIN_C7, ERRORS)

int8 capture_rising_edge;

int8 got_pulse_width;

int16 ccp_delta;

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#int_ccp1

void ccp1_isr(void) {

static int16 t1_rising_edge;

// If current interrupt is for rising edge.

if(capture_rising_edge) {setup_ccp1(CCP_CAPTURE_FE); capture_rising_edge = FALSE;

t1_rising_edge = CCP_1;

}

else {

setup_ccp1(CCP_CAPTURE_RE); capture_rising_edge = TRUE;ccp_delta = CCP_1 - t1_rising_edge; got_pulse_width = TRUE;

}

}

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main() {

int16 pulse_width_ms; int16 local_ccp_delta;

got_pulse_width = FALSE; capture_rising_edge = TRUE;

setup_ccp1(CCP_CAPTURE_RE);

setup_timer_1(T1_INTERNAL | T1_DIV_BY_8 );enable_interrupts(INT_CCP1); enable_interrupts(GLOBAL);

while(1) {

if(got_pulse_width) {

disable_interrupts(GLOBAL); local_ccp_delta = ccp_delta;

enable_interrupts(GLOBAL); pulse_width_ms = local_ccp_delta / 125;putc(254); putc(1); delay_ms(10);

printf("%lu ms \n\r", pulse_width_ms); got_pulse_width = FALSE;

}

}

} 8




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Compare Mode

In Compare mode, the 16-bit CCPR1 register value is

constantly compared against the TMR1 register pair

value. When a match occurs, the RC2/CCP1 pin is:

• Driven high

• Driven low

• Remains unchanged

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COMPARE MODE OPERATION BLOCK

DIAGRAM

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Compare Mode



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#include<16f877a.h>

#fuses XT,NOLVP,NOWDT,PUT


#use rs232(baud=9600,xmit=PIN_C6,rcv=PIN_C7)

#define high_start 2 //25

unsigned int8 seconds, high_count;

#INT_CCP1 //Interrupt procedure

clock_isr() {

high_count -= 1;

if(high_count==0) {

++seconds; if (seconds==60) seconds=0;

high_count=high_start;

putc(254); putc(1); delay_ms(10);

printf("%u seconds \n\r", seconds);

}}

Compare Mode



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void main() {

delay_ms(500); putc(254); putc(1); delay_ms(10);

seconds=0;

printf("%u seconds \n\r", seconds);

high_count = high_start;

setup_ccp1 (CCP_COMPARE_INT);

setup_timer_1(T1_INTERNAL | T1_DIV_BY_8 );

set_timer1(0);

CCP_1=5000;

enable_interrupts(INT_CCP1);

enable_interrupts(GLOBAL);

while(TRUE) {} ;

}

Compare Mode



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Pulse Width Modulation

PWM Mode

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In Pulse Width

Modulation mode, the

CCPx pin produces up

to a 10-bit resolution

PWM output





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PWM output

#include "16F877A.h"

void main()

{setup_ccp1(ccp_pwm);

setup_timer_2(T2_DIV_BY_16,250,1);

set_pwm1_duty(500);

while(1){}

}

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duty cycle = value / [ 4 * (PR2 +1 ) ]



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Demo PWM output

#include "16F877A.h"#fuses XT,NOLVP,NOWDT,PUT


unsigned int8 current_duty, old_duty;

void main() {

current_duty = 128; old_duty = 0;

setup_ccp1(ccp_pwm); setup_timer_2(T2_DIV_BY_16,250,1);

set_pwm1_duty(current_duty);

while (1) {

if (!input(PIN_A0)) current_duty +=5;

if (!input(PIN_A1)) current_duty-=5 ;

if (old_duty != current_duty) {set_pwm1_duty(current_duty);

old_duty = current_duty; OUTPUT_B(old_duty);

}

Delay_ms(200);

}

} 18



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Demo PWM output

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7 Capture Compare PWM