PIC16F882-I Datasheet, PDF (225/328 Pages) Microchip Technology – 28/40/44-Pin, Enhanced Flash-Based 8-Bit CMOS Microcontrollers

PIC16F882/883/884/886/887
14.4 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.
Since the upper 16 bytes of all GPR banks are com-
mon in the PIC16F882/883/884/886/887 (see
Figures 2-2 and 2-3), 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 14-1 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 PIC16F882/883/884/886/887 nor-
mally 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 14-1: SAVING STATUS AND W REGISTERS IN RAM
MOVWF W_TEMP
SWAPF STATUS,W
MOVWF STATUS_TEMP
:
:(ISR)
:
SWAPF STATUS_TEMP,W
MOVWF STATUS
SWAPF W_TEMP,F
SWAPF W_TEMP,W
;Copy W to TEMP register
;Swap status to be saved into W
;Swaps are used because they do not affect the status bits
;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
© 2009 Microchip Technology Inc.
DS41291F-page 223