PIC876 datasheet(132/218 Pages) MICROCHIP

132 / 218 page

PIC16F87X

DS30292C-page 130

 2001 Microchip Technology Inc.

12.10.1

INT INTERRUPT

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

either rising, if bit INTEDG (OPTION_REG<6>) is set,

or falling, 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 12.13 for details on SLEEP

mode.

12.10.2

TMR0 INTERRUPT

An overflow (FFh

→ 00h) in the TMR0 register will set

flag bit T0IF (INTCON<2>). The interrupt can be

enabled/disabled by setting/clearing enable bit T0IE

(INTCON<5>) (Section 5.0).

12.10.3

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>)

(Section 3.2).

12.11 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 register and STATUS

For the PIC16F873/874 devices, 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 0x20 in bank 0, it must

also be defined at 0xA0 in bank 1). The registers,

PCLATH_TEMP and STATUS_TEMP, are only defined

in bank 0.

Since the upper 16 bytes of each bank are common in

the PIC16F876/877 devices, temporary holding regis-

ters W_TEMP, STATUS_TEMP, and PCLATH_TEMP

should be placed in here. These 16 locations don’t

require banking and therefore, make it easier for con-

text save and restore. The same code shown in

Example 12-1 can be used.

EXAMPLE 12-1:

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

MOVF

PCLATH, W

;Only required if using pages 1, 2 and/or 3

MOVWF

PCLATH_TEMP

;Save PCLATH into W

CLRF

PCLATH

;Page zero, regardless of current page

:(ISR)

;(Insert user code here)

MOVF

PCLATH_TEMP, W

;Restore PCLATH

MOVWF

PCLATH

;Move W into PCLATH

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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