Using Timer0 Overflow Interrupt of PIC16F877A to Drive Multiplexing Display

I have showed an example of Timer 0 interrupt programming of PIC16F877A  in an earlier post. Here I use timer 0 interrupt to drive a multiplexing seven-segments display. This method is very effective in any application that contain many tasks polling.

In this example, timer 0 overflow interrupt will create a timer tick around 2.56 milliseconds. This timer tick regularly activate each digits of the multiplexing seven-segment display. 

Sample program

In main program loop, the program just check whenever the button is press. It will need to wait until the button is released until it increase the press counter. 

The display shows the counting content up to 60 before it reset to 0. The display show the counting content with any flickering due to the long-time button pressing.

Source Code:

/*
 * PIC16F877A Timer0 Interrupt and multiplexing
 * display example
 */
#include <xc.h>
#include "config.h"
 
//RB0 input button
#define SW1 RB0
 
unsigned int cnt=0,cntPress=0;
//Common cathode display pattern
char cCathode[10]={0x3F,0x06,0x5B,0x4F,0x66,0x6D,0x7D,0x07,0x7F,0x6F};
 
int main(void){  
    //Clear PortD
    PORTD=0x00;
    //Clear PortC
    PORTC=0x00;
    //Clear PortB
    PORTB=0x00;
    //PortD output
    TRISD=0x00;
    //PortC output
    TRISC=0x00;
    //RB0 is input
    TRISB0=1;
    //Turn on PortB Pullup resistors
    nRBPU=0;
    //select internal instruction cycle clock
    T0CS=0;
    //Select timer 0 prescaler
    PSA=0;
    //select 1:256 prescaler
    OPTION_REGbits.PS=0x07;
    //Enable timer0 interrupt
    T0IE=1;
    //Enable interrupt
    GIE=1;
    T0IF=0;
    //Clear Timer 0
    TMR0=0;
    while(1){       
        //Switch pressing count
        if(SW1==0){
            //Wait until it's release
            while(SW1==0);
            cntPress+=1;
        }
        if(cntPress>=60) cntPress=0;
    }
}
 
//Timer0 Interrupt Service Routine - ISR
void interrupt _T0_ISR(void){
    if(T0IF){
        //increase counter
        cnt+=1;
        //make a 10 mS time
        TMR0=-50;
        //Clear Flag
        T0IF=0;
    }
 
    switch(cnt){
            case 1:
                PORTC=0x00;
                PORTD=cCathode[cntPress/10];
                RC0=1;
                break;
 
            case 2:
                PORTC=0x00;
                PORTD=cCathode[cntPress%10];
                RC1=1;
                break;
 
            case 3:
                cnt=0;
                break;
        }   
}

Configuration bits:

 
// PIC16F877A Configuration Bit Settings
 
// CONFIG
// Oscillator Selection bits (HS oscillator)
#pragma config FOSC = HS
// Watchdog Timer Enable bit (WDT disabled)
#pragma config WDTE = OFF
// Power-up Timer Enable bit (PWRT disabled)
#pragma config PWRTE = OFF
// Brown-out Reset Enable bit (BOR enabled)
#pragma config BOREN = ON
/*
 * Low-Voltage (Single-Supply) In-Circuit Serial
 * Programming Enable bit (RB3 is digital I/O,
 * HV on MCLR must be used for programming)
 */
#pragma config LVP = OFF
/*
 * Data EEPROM Memory Code Protection bit
 * (Data EEPROM code protection off)
 */
#pragma config CPD = OFF
/*
 * Flash Program Memory Write Enable bits
 * (Write protection off; all program memory
 * may be written to by EECON control)
 */
#pragma config WRT = OFF
/*
 * Flash Program Memory Code Protection bit
 * (Code protection off)
 */
#pragma config CP = OFF
 
 
 

Schematic:

Using Timer0 Overflow Interrupt of PIC16F877A to Drive Multiplexing Display

Click here to download source file.