Using Reset pin of PIC16F887 as a digital input pin

The master clear reset ($MCLR) pin of PIC16F887 could be disabled. With the advantage of ignoring this external reset, we can use this pin (RE3) as a digital input only.

We can disable the $MCLR reset circuitry by clearing the MCRLE in the CONFIG1 configuration register. When it's cleared, the $MCLR pin is internally connected to VDD.

The 16-bit configuration word register 1 listed below:

BIT 15							BIT 8
N/A	N/A	$DEBUG	LVP	FCMEN	IESO	BOREN1	BOREN0

BIT 7							BIT 0
$CPD	$CP	MCLRE	$PWRTE	WDTE	FOSC2	FOSC1	FOSC0

In the XC8, we just use the "#pragma" directive to set the configuration like this:

#pragma config MCLRE = OFF

In this example, I use the RE3 pin as a digital input to count the external pulse. PortA used as a digital output port displaying the counting result on a single SSD. The OSC1 and OSC2 pin of PortA used as a digital output as a result of clocking the CPU from the internal RC oscillator with no clock out option.

Schematic diagram.
MCLR pin is internally pulled high.
RE3 is a digital input pin counting the button pressed.
PORTA output the counting result to a single SSD.

The XC8 source code:

#include<xc.h>
// PIC16F887 Configuration Bit Settings
// CONFIG1
#pragma config FOSC = INTRC_NOCLKOUT
#pragma config WDTE = OFF
#pragma config PWRTE = OFF
#pragma config MCLRE = OFF
#pragma config CP = OFF
#pragma config CPD = OFF
#pragma config BOREN = ON
#pragma config IESO = ON
#pragma config FCMEN = ON
#pragma config LVP = ON
// CONFIG2
#pragma config BOR4V = BOR40V
#pragma config WRT = OFF
#define _XTAL_FREQ 4000000
#define btnCount RE3
void main(void){
    unsigned char ssd[16]={0x3F,0x06,0x5B,0x4F,0x66,0x6D,0x7D,
        0x07,0x7F,0x6F,0x77,0x7C,0x39,0x5E,0x79,0x71};
    char countButton=0;
    /*Select 4 MHz internal Oscillator*/
    SCS=1;
    OSCCONbits.IRCF=0x06;
    /*clear PortA*/
    PORTA=0x00;
    /*set PortA to output*/
    TRISA=0x00;
    /*clear analog inputs*/
    ANSEL=0x00;
    while(1){
        if(btnCount==0){
            __delay_ms(250);
            countButton+=1;
        }
        if(countButton>15)
            countButton=0;
        PORTA=ssd[countButton];
    }
}

A screen shot the program simulation:

A simulation screen shot.
The counting result fed from RE3 reaches 6.

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