Generating PWM with PIC16F877A

PWM Interfacing With PIC16F877A Primer

Tags: Circuit Diagram to Interface PWM with PIC16F877A primer, C Program to generate PWM in PIC16F877A PWM using PIC16F877A,PWM source code for PIC Microcontrollers,
Overall rating
PIC16F/18F Primer Board

The PIC16F/18F Primer board is specifically designed to help students to master the required skills in the area of embedded systems. The kit is designed in such way that all the possible features of the microcontroller will be easily used by the students. The kit supports in system programming (ISP) which is done through USB port.

Microchip’s PIC (PIC16F877A), PIC16F/18F Primer Kit is proposed to smooth the progress of developing and debugging of various designs encompassing of High speed 8-bit Microcontrollers.

PWM (Pulse Width Modulation)

Pulse width modulation (PWM) is a powerful technique for controlling analog circuits with a processor's digital outputs. PWM is employed in a wide variety of applications, ranging from measurement and communications to power control and conversion.

Interfacing PWM

Figure 1 shows four different PWM signals. One is PWM output at a 25% duty cycle. That is, the signal is on for 25% of the period and off the other 75%. Next shows PWM output at 50%, 75% and 100% duty cycles, respectively. These three PWM outputs encode three different analog signal values, at 10%, 50%, and 90% of the full strength.


Fig. 1 PWM Outputs

Interfacing PWM with PIC16F877A

We now want to generate a PWM in PIC16F/18F Primer Board at a particular frequency. Pulse Width Modulation is a technique for getting analog results with digital means.

Digital control is used to create a square wave, a signal switched between on and off. This on-off pattern can simulate voltages in between full on (5 Volts) and off (0 Volts) by changing the portion of the time the signal spends on versus the time that the signal spends off. The duration of "on time" is called the pulse width. To get varying analog values, you change, or modulate, that pulse width.

Pin Assignment with PIC16F877A




PIC16F Lines





There are no connections on the




Output: Connect a CRO and measure the pulse width and duty cycle


Circuit Diagram to Interface PWM with PIC16F877A


Source Code

The Interfacing PWM with PIC16F877A program is very simple and straight forward, which generates a pulse pattern in a particular frequency. An ADC signal is used to varying the duty cycle of PWM signal. The C program is written in Mplab software & it executed with Hi-Tech C compiler.

C Program to generate PWM in PIC16F877A


Title : Program to generate PWM





#include<pic.h>   //Define PIC registers

   __CONFIG(0x3f72); //Select HS oscillator, Enable (PWRTE,BOREN),

                          //Disable (CPD,CP,WDTEN,In-circuit Debugger)


#define XTAL      10000     //10Mhz=10000Khz

#define PWM_Freq  1        //1Khz PWM frequency

#define TMR2_PRE  16       //Timer2 Prescale

#define PR2_Val     ((char)((XTAL/(4*TMR2_PRE*PWM_Freq))-1))                    

                 //Calculation for Period register PR2 (1Khz)


#define Duty_Cyc  PR2_Val*2


unsigned int i;


void PWM_init(void);

void PWM_change(unsigned int);

void DelayMs(unsigned int);

void main(void)

















void PWM_init(void)


   TRISC2=0;     //PWM channel 1 and 2 configured as output


   PORTC = 0x00;

   CCP1CON=0x0c; //CCP1 and CCP2 are configured for PWM


   PR2=PR2_Val;  //Move the PR2 value


   T2CON=0x03;   //Timer2 Prescale is 16


   TMR2ON=1;     //Turn ON timer2



void PWM_change(unsigned int DTY) //Duty cycle change routine


   CCPR1L=DTY;   //Value is between 0 to 255




void DelayMs(unsigned int Ms)   //Delay Routine


   int delay_cnst;






          for(delay_cnst = 0;delay_cnst <220;delay_cnst++);       

          //delay constant for 1Ms @10Mhz






To compile the above C code you need the Mplab software & Hi-Tech C Compiler. They must be properly set up and a project with correct settings must be created in order to compile the code. To compile the above code, the C file must be added to the project.

In Mplab, you want to develop or debug the project without any hardware setup. You must compile the code for generating HEX file. In debugging Mode, you want to check the port output without PIC16F/18F Primer Board.

The PICKIT2 software is used to download the hex file into your microcontroller IC PIC16F877A through USB port.

Testing the PWM with PIC16F877A

Give +12V power supply to PIC16F/18F Primer Board; the PWM port line is connected in PIC16F/18F Primer Board. When the program is downloading into PIC16F877A in Primer Board, the PWM output is generating at a particular frequency.

If you are not reading any PWM output, then you just check the jumper connections. Otherwise you just check it with debugging mode in Mplab. If you want to see more details about debugging just see the videos in below link.

General Information

Join the World's Largest Technical Community

we respect your privacy.