PIC16F887 Interrupt-On-Change in MikroC

Introduction

Port B of PIC16F887 is individually able to trigger interrupt signal to the controller. It's called INTERRUPT-ON-CHANGE. It also cover the external interrupt on RB0. However this interrupt source comes with most of new version of PIC microcontroller.

There are some registers relate to this interrupt source, IOCB, and INTCON.

Interrupt Control Register - INTCON

This register contains control and flag bit of interrupt-on-change.

Interrupt Control Register (INTCON)

Set the Global Interrupt Enable bit (GIE) to turn on interrupt for PIC16F887 microcontroller. Bit 3 is called PORTB Change Interrupt Enable bit (RBIE). This bit must be set to turn on the PortB-Interrupt-On-Change. RBIF is PORTB Change Interrupt Flag bit. In the ISR the program must test this bit for its interrupt request.

Interrupt-On-Change PORTB Register - IOCB

This 8-bit wide special function register configures the present of PortB-Interrupt-On-Change.

Interrupt-On-Change PortB Register - IOCB

It corresponds to all 8 pins of PortB. It can be individually turn on and off up to the user.

IOCB of PIC16F887 Programming in MikroC

Introduction

There are some more register to make this programming work well. Port B weak pull up resistors must be turned on to save component counts. This job will be done with the OPTION_REGand the WBPU register.

Its internal oscillator with a frequency of 8MHz could fit this simple task. Program will need to configure the OSCCON register to select its 8MHz internal oscillator.

Unlike external interrupt, this interrupt source doesn't have edge selection control bit. Its interrupt flag RBIF is set at the instance of port reading mismatch the previous port value.

Hardware

I made its schematic in Proteus due to its ease of design.

Schematic Diagram

SW1 connects to RB7 creates interrupt when it's pressed (shorted to ground). D1 toggles each time the interrupt occurs.

Programming in MikroC

The controller is configured to clock from its internal 8MHz oscillator. Port B input doesn't need external pull up resistor since it's internally connected to its weak pull up resistor by software.

Interrupt-On-Change occurs when the input logic to RB7 change from high to low.

void interrupt() {
     if(INTCON.RBIF)
        if(PORTB.RB7==0) // check if RB7 is shorted to GND
        PORTB.RB0^=1;
     INTCON.RBIF=0;
     }
 
void main() {
     PORTB=0x00;                // CLEAR PORTB
     TRISB=0x80;                 // RB7 IS INPUT
     ANSELH=0x00;                // DISABLE ALL ANALOG FUNCTION
     OPTION_REG.F7=0;            // ENABLE WPUB
     WPUB=0x80;               // TURN ON WPUB FOR RB7
     OSCCON|=0x70;            // SELECT INTRCIO 8MHz
     INTCON.GIE=1;            // TURN ON GLOBAL INTERRUPT
     INTCON.RBIE=1;           // TURN ON IOCB
     IOCB=0x80;               // RB7 IS USE TO CREATE INTERRUPT
     INTCON.RBIF=0;           // CLEAR INTERRUPT FLAG
     while(1);                // STAY HERE
}

Both MikroC and Proteus simulation were recorded in this video.