Port B Weak Pullup Resistors of PIC18F1220

 

Introduction

Port B of PIC18F1220 has an internal programmable weak pull up resistors. However it’s not individually select-able. These resistors have only one shared global switch locates in OPTION Register.

Pin diagram of PIC18F1220

Additionally, this port is multiplexed with ADC input. To configure it to a solely digital I/O, the user must check the ADCON1 register.

Interfacing and Programming

Using a simulator to simulate the circuit, the overall prototyping is fast and effective. It reduces cost, time and physical hardware defect.

Hardware Interfacing

PIC18F1220 microcontroller accept digital input on lower nibble of Port B. Its higher nibble connects to LED representing the digital input on lower nibble.

Schematic Diagram

Programming

At setting up section of C main program, programmer need to clear port I/O, disabling analog input function, setting up port direction, and turning on Port B weak pull up resistors.

C

/*

 * PIC18F1220 Weak Pull Up Resistor

 * And Disabling Analog Input on Port B

 */

#include <xc.h>

#include "config.h"

​

void main(void){

    /*Clear Port B IO*/

    PORTB=0x00;

    LATB=0x00;

    /*Disable Analog Input Function*/

    ADCON1=0x70;

    /*RB0...3 digital input*/

    TRISB=0x0F;

    /*Turn on Weak Pull Up*/

    nRBPU=0;

    while(1){

        PORTB<<=4;

    }

}

PIC18F1220 configuration bits setting is very long that programmer doesn’t want to put inside C main file.

C

// PIC18F1220 Configuration Bit Settings

​

// CONFIG1H

#pragma config OSC = XT         // Oscillator Selection bits (XT Oscillator)

#pragma config FSCM = ON        // Fail-Safe Clock Monitor Enable bit (Fail-Safe Clock Monitor enabled)

#pragma config IESO = ON        // Internal External Switchover bit (Internal External Switchover mode enabled)

​

// CONFIG2L

#pragma config PWRT = OFF       // Power-up Timer Enable bit (PWRT disabled)

#pragma config BOR = ON         // Brown-out Reset Enable bit (Brown-out Reset enabled)

// BORV = No Setting

​

// CONFIG2H

#pragma config WDT = OFF        // Watchdog Timer Enable bit (WDT disabled (control is placed on the SWDTEN bit))

#pragma config WDTPS = 32768    // Watchdog Timer Postscale Select bits (1:32768)

​

// CONFIG3H

#pragma config MCLRE = ON       // MCLR Pin Enable bit (MCLR pin enabled, RA5 input pin disabled)

​

// CONFIG4L

#pragma config STVR = ON        // Stack Full/Underflow Reset Enable bit (Stack full/underflow will cause Reset)

#pragma config LVP = OFF        // Low-Voltage ICSP Enable bit (Low-Voltage ICSP disabled)

​

// CONFIG5L

#pragma config CP0 = OFF        // Code Protection bit (Block 0 (00200-0007FFh) not code-protected)

#pragma config CP1 = OFF        // Code Protection bit (Block 1 (000800-000FFFh) not code-protected)

​

// CONFIG5H

#pragma config CPB = OFF        // Boot Block Code Protection bit (Boot Block (000000-0001FFh) not code-protected)

#pragma config CPD = OFF        // Data EEPROM Code Protection bit (Data EEPROM not code-protected)

​

// CONFIG6L

#pragma config WRT0 = OFF       // Write Protection bit (Block 0 (00200-0007FFh) not write-protected)

#pragma config WRT1 = OFF       // Write Protection bit (Block 1 (000800-000FFFh) not write-protected)

​

// CONFIG6H

#pragma config WRTC = OFF       // Configuration Register Write Protection bit (Configuration registers (300000-3000FFh) not write-protected)

#pragma config WRTB = OFF       // Boot Block Write Protection bit (Boot Block (000000-0001FFh) not write-protected)

#pragma config WRTD = OFF       // Data EEPROM Write Protection bit (Data EEPROM not write-protected)

​

// CONFIG7L

#pragma config EBTR0 = OFF      // Table Read Protection bit (Block 0 (00200-0007FFh) not protected from table reads executed in other blocks)

#pragma config EBTR1 = OFF      // Table Read Protection bit (Block 1 (000800-000FFFh) not protected from table reads executed in other blocks)

​

// CONFIG7H

#pragma config EBTRB = OFF      // Boot Block Table Read Protection bit (Boot Block (000000-0001FFh) not protected from table reads executed in other blocks)

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