MCP19116-ESLASHMJ datasheet(113/246 Pages) MICROCHIP

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DS20005479B-page 113

MCP19116/7

15.4

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.

Temporary

holding

registers

W_TEMP

and

STATUS_TEMP should be placed in the last 16 bytes

of GPR. These 16 locations are common to all banks

and do not require banking. This makes context save

and restore operations simpler. The code shown in

Example 15-1 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 15-1:

SAVING STATUS AND W REGISTERS IN RAM

Note:

The MCP19116/7 devices do not require

saving the PCLATH. However, if com-

puted GOTOs are used in both 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

;Swaps are used because they do not affect the status bits

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

MCP19116-E/MJ Datasheet(PDF) 113 Page - Microchip Technology

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