PIC16F877A Basic Digital I/O Port Programming

Introduction

In previous section we getting started with PIC16F877A with LED toggling on Port C. Now let move to its digital I/O port programming using XC8.

PIC16F877A has up to five digital I/O ports,

• Port A
• Port B
• Port C
• Port D
• and Port E

These ports are bi-directional I/O by program setting.

PIC16F877A pin diagram

Port C and Port D

These two ports are discussed first due to their pure digital I/O functions.

Port C

Port C locates at 07h in Special Function Register (SFR). Its data direction is controlled by TRISC register, locates at 87h in SFR.

Registers associate with Port C

Setting TRISC conveys Port C to input direction, accepting digital input data from outside world. Clearing TRISC to make Port C outputs its data via its output pins.

Port D

Port D locates at 08h in SFR. Its data direction is controlled by TRISD register, locates at 88h in SFR.

Setting TRISD conveys Port D to input direction, accepting digital data from outside world. Clearing this register to make Port D to outputs its data from its output pins.

Registers associate with Port D

Port D has another digital function – 8-bit wide microprocessor microprocessor port (Parallel Slave Port).

Programming Example

A simple example shows how to read digital input Port C. Its digital data outputs on Port D.

Schematic Diagram

Digital input made by a DIP switch with a resistor network. Digital output is an LED bar-graph.

/*
 * PIC16F877A digital I/O Programming in XC8
 */
#include <xc.h>
 
// PIC16F877A Configuration Bit Settings
// CONFIG
#pragma config FOSC = HS        // Oscillator Selection bits (HS oscillator)
#pragma config WDTE = OFF       // Watchdog Timer Enable bit (WDT disabled)
#pragma config PWRTE = OFF      // Power-up Timer Enable bit (PWRT disabled)
#pragma config BOREN = ON       // Brown-out Reset Enable bit (BOR enabled)
#pragma config LVP = OFF        // 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 CPD = OFF        // Data EEPROM Memory Code Protection bit (Data EEPROM code protection off)
#pragma config WRT = OFF        // Flash Program Memory Write Enable bits (Write protection off; all program memory may be written to by EECON control)
#pragma config CP = OFF         // Flash Program Memory Code Protection bit (Code protection off)
 
void main(void){
    /*Clear IO*/
    PORTC=0x00;
    PORTD=0x00;
    /*Port C input*/
    TRISC=0xFF;
    /*Port D output*/
    TRISD=0x00;
    while(1){
        PORTD=PORTC;
        for(int i=0;i<25;i++);
    }
}

 Click here to download zip file of this programming example.

Port B

Port B is an 8-bit wide bi-directional I/O. Its data direction is controlled by TRISD register. PORTB is its I/O register locate at 07h in SFR. TRISB locates at 87h.

Details

Setting TRISB allows Port B to accept digital input data, as it works in input data direction. By clearing it, digital data flows out via PORTB I/O register to output devices.

Register associate with Port B

RB0 of Port B can trigger an external interrupt but we don’t discuss it here. Port B has an internal weak pull up resistors. This feature is enabled by clearing RBPU bit of Option Register (OPTION_REG).

Programming Example

We will show how to configure Port B as digital input with its internal weak pull up resistors. Here Port D is a digital output port connecting to bar-graph LED.

Port B doesn’t need external resistors as it’s internally connected to VDD via its weak pull up resistors.

/*
 * PIC16F877A Port B digital I/O Programming in XC8
 */
#include <xc.h>
 
// PIC16F877A Configuration Bit Settings
// CONFIG
#pragma config FOSC = HS        // Oscillator Selection bits (HS oscillator)
#pragma config WDTE = OFF       // Watchdog Timer Enable bit (WDT disabled)
#pragma config PWRTE = OFF      // Power-up Timer Enable bit (PWRT disabled)
#pragma config BOREN = ON       // Brown-out Reset Enable bit (BOR enabled)
#pragma config LVP = OFF        // 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 CPD = OFF        // Data EEPROM Memory Code Protection bit (Data EEPROM code protection off)
#pragma config WRT = OFF        // Flash Program Memory Write Enable bits (Write protection off; all program memory may be written to by EECON control)
#pragma config CP = OFF         // Flash Program Memory Code Protection bit (Code protection off)
 
void main(void){
    /*Clear IO*/
    PORTB=0x00;
    PORTD=0x00;
    /*Port B input*/
    TRISB=0xFF;
    /*Turn on Weak Pull Up*/
    OPTION_REGbits.nRBPU=0;
    /*Port C output*/
    TRISD=0x00;
    while(1){
        PORTD=PORTB;
        for(int i=0;i<25;i++);
    }
}

 Click here to download this example is zip format. 

Port A

Port A is an 8-bit wide bi-directional I/O. Its data direction is controlled by TRISA register.

Details

PORTA is its I/O buffer locates at 05h in SFR. Its data direction control TRISA locates at 85h in SFR. Setting TRISA make this port as digital input, otherwise it becomes digital output.

Registers associate with Port A

Port A is multiplexed with Analog to Digital Converter (ADC) input. Setting Analog to Digital Control Register 1 (ADCON1) to 0x06 to analog input function, allowing this port work solely in digital I/O.

Programming Example

We make a simple port reading from Port A. Its digital value will be displayed on Port B.

Schematic diagram and its simulation

Port A is usable only five bits. So I mask other two remaining MSB.

/*
 * PIC16F877A Port A Programming Example in XC8
 */
#include <xc.h>
 
// PIC16F877A Configuration Bit Settings
// CONFIG
#pragma config FOSC = HS        // Oscillator Selection bits (HS oscillator)
#pragma config WDTE = OFF       // Watchdog Timer Enable bit (WDT disabled)
#pragma config PWRTE = OFF      // Power-up Timer Enable bit (PWRT disabled)
#pragma config BOREN = ON       // Brown-out Reset Enable bit (BOR enabled)
#pragma config LVP = OFF        // 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 CPD = OFF        // Data EEPROM Memory Code Protection bit (Data EEPROM code protection off)
#pragma config WRT = OFF        // Flash Program Memory Write Enable bits (Write protection off; all program memory may be written to by EECON control)
#pragma config CP = OFF         // Flash Program Memory Code Protection bit (Code protection off)
 
void main(void){
    /*Clear IO*/
    PORTB=0x00;
    PORTA=0x00;
    /*Port A input*/
    TRISA=0xFF;
    /*Disable ADC input*/
    ADCON1=0x06;
    /*Port B output*/
    TRISB=0x00;
    while(1){
        /*Read Port A input*/
        PORTB=PORTA&0b00111111;
        /*A little delay*/
        for(int i=0;i<10;i++);
    }
}

 Click here to download this example program.