PIC16F946 Datasheet, PDF (207/274 Pages) Microchip Technology – 64-Pin Flash-Based, 8-Bit CMOS Microcontrollers with LCD Driver and nanoWatt Technology

PIC16F946
16.5 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
PIC16F946 (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 16-1
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
Note:
The PIC16F946 normally does not require
saving the PCLATH. However, if
computed GOTO’s are used in the ISR and
the main code, the PCLATH must be
saved and restored in the ISR.
EXAMPLE 16-1: SAVING STATUS AND W REGISTERS IN RAM
MOVWF
SWAPF
CLRF
MOVWF
:
:(ISR)
:
SWAPF
W_TEMP
STATUS,W
STATUS
STATUS_TEMP
STATUS_TEMP,W
MOVWF
SWAPF
SWAPF
STATUS
W_TEMP,F
W_TEMP,W
;Copy W to TEMP register
;Swap status to be saved into W
;bank 0, regardless of current bank, Clears IRP,RP1,RP0
;Save status to bank zero STATUS_TEMP register
;Insert user code here
;Swap STATUS_TEMP register into W
;(sets bank to original state)
;Move W into Status register
;Swap W_TEMP
;Swap W_TEMP into W
© 2005 Microchip Technology Inc.
Preliminary
DS41265A-page 205