12F683 datasheet(90/148 Pages) MICROCHIP

90 / 148 page

PIC12F683

DS41211B-page 88

Preliminary

 2004 Microchip Technology Inc.

12.5

Context Saving During Interrupts

During an interrupt, only the return PC value is saved

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

registers during an interrupt (e.g., W and Status

registers). This must be implemented in software.

Since the lower 16 bytes of all banks are common in the

PIC12F683 (see Figure 2-2), temporary holding regis-

ters, W_TEMP and STATUS_TEMP, should be placed

in here. These 16 locations do not require banking and

therefore, makes it easier to context save and restore.

The same code shown in Example 12-1 can be used

to:

• Store the W register.

• Store the Status register.

• Execute the ISR code.

• Restore the Status (and Bank Select Bit register).

• Restore the W register.

EXAMPLE 12-1:

SAVING STATUS AND W REGISTERS IN RAM

Note:

The PIC12F683 normally does not require

saving the PCLATH. However, if com-

puted GOTOs are used in the ISR and the

main code, the PCLATH must be saved

and restored in the ISR.

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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