PIC16F871-E/L【PDF 3/143 页】IC MCU CMOS 20MHZ 2K FLSH 44PLCC

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PIC16F870/871

DS30569B-page 98

2003 Microchip Technology Inc.

11.11 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 PIC16F870/871 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 PIC16F870/871 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 11-1 can be used.

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

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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