PIC16F684-ESLASHST datasheet(106/164 Pages) MICROCHIP

106 / 164 page

PIC16F684

DS41202C-page 104

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

PIC16F684

(see

Figure 2-2),

temporary

holding

registers, W_TEMP and STATUS_TEMP, should be

placed in here. These 16 locations do not require

banking and therefore, make 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 PIC16F684 normally does not require

saving

the

PCLATH.

However,

computed 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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