PIC16F84A datasheet(49/124 Pages) MICROCHIP

49 / 124 page

PIC16F8X

DS30430C-page 49

8.10

Context Saving During Interrupts

During an interrupt, only the return PC value is saved

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

values during an interrupt (e.g., W register and STATUS

Example 8-1 stores and restores the STATUS and W

and STATUS_TEMP are the temporary storage

locations for the W and STATUS registers values.

Example 8-1 does the following:

Stores the W register.

Stores the STATUS register in STATUS_TEMP.

Executes the Interrupt Service Routine code.

Restores the STATUS (and bank select bit)

Restores the W register.

EXAMPLE 8-1:

SAVING STATUS AND W REGISTERS IN RAM

PUSH

MOVWF

W_TEMP

; Copy W to TEMP register,

SWAPF

STATUS, W

; Swap status to be saved into W

MOVWF

STATUS_TEMP

; Save status to STATUS_TEMP register

ISR

; Interrupt Service Routine

;

should configure Bank as required

;

POP

SWAPF

STATUS_TEMP, W

; Swap nibbles in STATUS_TEMP register

; and place result into W

MOVWF

STATUS

; Move W into STATUS register

;

(sets bank to original state)

SWAPF

W_TEMP, F

; Swap nibbles in W_TEMP and place result in W_TEMP

SWAPF

W_TEMP, W

; Swap nibbles in W_TEMP and place result into W

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