Radboud,

Since you do not know which Bank was selected when the interrupt
happens, the standard PIC trick is to save W in whatever bank is
current, then grab STATUS into W.  Then you can save everything else.

You need to remember that that location is "used" in all RAM banks so
that it is set aside for saving W.  So use different variable names
in each bank, but make sure that there is one in each bank at that
address.  I use the lowest address in each page.

example:
...
;First bank of RAM
;          ORG     H'20'               ;general purpose RAM starts at
020h
;ISRs cannot know which bank of RAM is selected when interrupt
occurs,
;so WSave is allocated in both banks.
WSave      EQU     H'20'               ;020h: ISR Save Area for W
StatSave   EQU     H'21'               ;021h: Save Area for STATUS
PCHSave    EQU     H'22'               ;ISR save area for PCLATH
FSRSave    EQU     H'23'               ;ISR save area for FSR

...

;Second bank of RAM
;Generated RAM addresses are the SAME as bank 0, program must set RP0
;to use these variables.
;ISRs cannot know which bank of RAM is selected when an interrupt
occurs,
;so WSave is allocated in both banks.
WSave1     EQU     H'A0'               ;0A0h: Duplicate ISR Save Area
for W

...
IntSvc     MOVWF   WSave               ;Save W.  Don't know which
bank used
           SWAPF   STATUS, W           ;use SWAP to move unmodified
STATUS
                                       ;bits (nybbles swapped) into W
           BCF     STATUS, RP0         ;switch to RAM bank 0
           BCF     STATUS, RP1         ;
           MOVWF   StatSave            ;save (nybble swapped) copy of
STATUS
;Must save PCLATH of interrupted code so that code in other than page
0 EPROM
;can be interrupted and restore correctly
           MOVF    PCLATH, W           ;get PCLATH of interrupted
code
           MOVWF   PCHSave             ;save it
           CLRF    PCLATH              ;set PCLATH to xxx00000b for
ISR
;Save FSR of interrupted code
           MOVF    FSR, W              ;Get FSR of interrupted code
           MOVWF   FSRSave             ;save it

;Find out who interrupted.  Scan for highest priority first.
...

---------------------------------------------------
Barry King
Engineering Manager
NRG Systems "Measuring the Wind's Energy"
barry@nrgsystems.com
"The witty saying has been deleted due to limited EPROM space"