Prerequisites

Please check this tutorial for detailed explanation on PIC18F4520 PWM module.

PIC18F4520 PWM Module

PIC18F4520 microcontroller has two independent CCP(Capture/Compare/PWM) modules, named as CCP1 and CCP2. Each CCP module has two 8-bit resistors(CCPxH,CCPxL) that can be use as:

16 bit Capture Register
16 bit Compare Register
10-bit PWM Register.

In this tutorial we will be discussing only the PWM part of CCP. PIC has 2PWM module with a resolution of 10-bits.
Below tables shows the PWM module of PIC.

PWM Channel	Port Pin	Control Register	Duty Cycle Register	Period Register
PWM1	PC.2	CCP1CON	CCPR1L	PR2
PWM2	PC.1	CCP2CON	CCPR2L	PR2

Code1

Below is the example to vary the brightness of the LED(PC.2) using PWM.

	#include "pwm.h"
	#include "delay.h"


	/* start the main program */
	int main()
	{
	int dutyCycle;

	PWM_Init(0); /* Initialize the PWM module and the Cycle time(Ton+Toff) is set to 100*/
	PWM_Start(0); /* Start PWM signal generation on Selected pin */

	while(1)
	{

	for(dutyCycle=0;dutyCycle<100;dutyCycle++) /* Increase the Brightness of the LED */
	{
	PWM_SetDutyCycle(0,dutyCycle);
	DELAY_ms(5);
	}

	for(dutyCycle=100;dutyCycle>0;dutyCycle--) /* Decrease the Brightness of the LED */
	{
	PWM_SetDutyCycle(0,dutyCycle);
	DELAY_ms(5);
	}
	}
	}

view raw pic16f877a_pwmLedFade.c hosted with ❤ by GitHub

Code2

Progarm to generate the PWM signals of 25% & 75% duty cycle.

	#include "pwm.h"
	#include "stdutils.h"


	/* start the main program */
	int main()
	{
	PWM_Init(0); // Initialize the PWM modules
	PWM_Init(1);

	PWM_SetDutyCycle(0,25); //Set the Duty Cycle of 25% for PWM1->RC2
	PWM_SetDutyCycle(1,75); //Set the Duty Cycle of 25% for PWM2->RC1

	PWM_Start(0); //Start the PWM signal generation
	PWM_Start(1);

	while(1);
	}