Файл: Microcontroller Programming. Thi Micro Chip PIC (Julio Sanchez, 2007).pdf

RB4-7 Change Interrupt Service Routine

The Service Routine for the RB4-7 change interrupt depends on the specific application. Nevertheless, the following processing steps should be considered:

1.Determine if the source is an RB4-7 change interrupt.

2.Clear the RBIF interrupt flag in the INTCON Register.

3.Save the context. Which registers and variables need to be saved depends on the specific application.

4.Perform the interrupt action.

5.Restore the context.

6.Return from the interrupt with the retfie instruction.

In addition, the interrupt handler may have to perform operations that are specific to the application; for example, debounce a switch or initialize local variables. The following Interrupt Service routine is from the program RB4to7Int in the book’s online software:

;=======================================================

;=======================================================

;Service routine receives control whenever any of

;port-B lines 4 to 7 change state

IntServ:

; First test: make sure source is an RB4-7 interrupt

;=========================

;interrupt action ;=========================

;The interrupt occurs when any of port-B bits 4 to 7

;have changed status.

; Test each meaningful bit (4 and 7 in this example)

;========================

;bit 4 change routine ;========================

;Check for signal falling edge, ignore if not bit4Chng:

;bit 7 change routine ;========================

;Check for signal falling edge, ignore if not bit7Chng:

;At this point all port-B pushbuttons are released ;=========================

;exit ISR

Processing by the interrupt service routine is straightforward. The code first determines which line caused the interrupt and takes the corresponding action in each case. In either case, the handler waits until all pushbuttons have been released before returning from the interrupt. This serves to debounce the switches.

11.4 Sample Programs

The following programs demonstrate the programming discussed in this chapter.

11.4.1 The RB0Int Program

;File: RB0Int.ASM

;Date: April 22, 2006

;Author: Julio Sanchez

;Processor: 16F84A

;Description:

;Program to test interrupt on port RB0

;A pushbutton switch is connected to port RB0.

;The pushbutton toggles a LED on port-B, line 2

;Another LED on port-B, line 1, flashes on and off

;at 1/2 second intervals ;===========================

;switches

;===========================

; Switches used in __config directive:

;_PWRTE_OFF

error)

;|

;|_____ * indicates setup values

;========================= ; setup and configuration ;=========================

processor 16f84A include <p16f84A.inc>

__config _XT_OSC & _WDT_OFF & _PWRTE_ON & _CP_OFF ;=====================================================

;

;============================= ; interrupt handler ;=============================

org 0x04 goto IntServ

;=============================

;main program ;============================= main:

;Set up interrupt on falling edge

;by clearing OPTION register bit 6

;setup interrupts ;============================

;Clear external interrupt flag (INTF = bit 1)

;Enable global interrupts (GIE = bit 7)

;Enable RB0 interrupt (INTE = bit 4)

;============================