Four of the PORTB pins, RB7:RB4, have an interrupt-on-change (IOC) feature. Only pins configured as inputs can cause this interrupt to occur (i.e., any RB7:RB4 pin configured as an output is excluded from the interrupt-on-change comparison). The input pins (of RB7:RB4)
are compared with the old value latched on the last read of PORTB. The “mismatch” outputs of RB7:RB4 are OR’ed together to generate the RB port change interrupt with flag bit RBIF (INTCON<0>).
This interrupt can wake the device from Sleep. The user, in the Interrupt Service Routine, can clear the interrupt in the following manner:
a) Any read or write of PORTB. This will end the
mismatch condition.
b) Clear flag bit RBIF.
A mismatch condition will continue to set flag bit RBIF. Reading PORTB will end the mismatch condition and allow flag bit RBIF to be cleared. The interrupt-on-change feature is recommended for wake-up on key depression operation and operations where PORTB is only used for the interrupt-on-change feature. Polling of PORTB is not recommended while
using the interrupt-on-change feature.
PIC16F877A PORTB change interrupt example:
This is a small example shows how to use the interrupt-on-change feature of PIC16F877A. Circuit schematic is below:
PIC16F877A PORTB change interrupt example CCS C code:
// PIC16F877A RB change interrupt
// http://ccspicc.blogspot.com/
// electronnote@gmail.com
#include <16F877A.h>
#use delay(crystal=8000000)
byte i;
#INT_RB
void rb_isr(void)
{
i = input_b();
output_d(i >> 4);
}
void main()
{
set_tris_b(0xF0);
clear_interrupt(INT_RB);
enable_interrupts(INT_RB);
enable_interrupts(GLOBAL);
while(TRUE) ; // Endless loop
}
PIC16F877A PORTB change interrupt example simulation video:
The following video shows simulation using Proteus with some descriptions.
Reference:
PIC16F877A datasheet.
