OPTION_REG datasheet(98/222 Pages) MICROCHIP

98 / 222 page

MCP19111

DS22331A-page 98

 2013 Microchip Technology Inc.

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 (see Figure 11-2). 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 MCP19111 device does not require

saving

the

PCLATH.

However,

computed 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

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