PIC16F72SLASHML datasheet(71/136 Pages) MICROCHIP

71 / 136 page

 2002 Microchip Technology Inc.

DS39597B-page 69

PIC16F72

11.11.1

INT INTERRUPT

External interrupt on the RB0/INT pin is edge triggered,

either rising, if bit INTEDG (OPTION<6>) is set, or fall-

ing, if the INTEDG bit is clear. When a valid edge

appears

the

RB0/INT

pin,

flag

bit

INTF

(INTCON<1>) is set. This interrupt can be disabled by

clearing enable bit INTE (INTCON<4>). Flag bit INTF

must be cleared in software in the Interrupt Service

Routine before re-enabling this interrupt. The INT inter-

rupt can wake-up the processor from SLEEP, if bit INTE

was set prior to going into SLEEP. The status of global

interrupt enable bit GIE decides whether or not the

processor branches to the interrupt vector following

wake-up. See Section 11.14 for details on SLEEP

mode.

11.11.2

TMR0 INTERRUPT

An overflow (FFh

→ 00h) in the TMR0 register will set

flag bit TMR0IF (INTCON<2>). The interrupt can be

enabled/disabled

setting/clearing

enable

bit

TMR0IE (INTCON<5>) (see Section 5.0).

11.11.3

PORTB INTCON CHANGE

An input change on PORTB<7:4> sets flag bit RBIF

(INTCON<0>). The interrupt can be enabled/disabled

by setting/clearing enable bit RBIE (INTCON<4>) (see

Section 3.2).

11.12 Context Saving During Interrupts

During an interrupt, only the return PC value is saved

on the stack. Typically, users may wish to save key reg-

isters during an interrupt (i.e., W, STATUS registers).

This will have to be implemented in software, as shown

in Example 11-1.

For the PIC16F72 device, the register W_TEMP must

be defined in both banks 0 and 1 and must be defined

at the same offset from the bank base address (i.e., if

W_TEMP is defined at 20h in bank 0, it must also be

defined at A0h in bank 1). The register STATUS_TEMP

is only defined in bank 0.

EXAMPLE 11-1:

SAVING STATUS, W AND PCLATH REGISTERS IN RAM

MOVWF

W_TEMP

;Copy W to TEMP register

SWAPF

STATUS,W

;Swap status to be saved into W

CLRF

STATUS

;bank 0, regardless of current bank, Clears IRP,RP1,RP0

MOVWF

STATUS_TEMP

;Save status to bank zero STATUS_TEMP register

:(ISR)

;Insert user code here

SWAPF

STATUS_TEMP,W

;Swap STATUS_TEMP register into W

;(sets bank to original state)

MOVWF

STATUS

;Move W into STATUS register

SWAPF

W_TEMP,F

;Swap W_TEMP

SWAPF

W_TEMP,W

;Swap W_TEMP into W

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