Hi, I am trying to learn about context saving in assembly language. I have 16F72 with me for which I am trying to write an ISR in assembly. I am having a little trouble in understanding the variable declaration part. What I have written upto now is this:
The above is an unreliable code which is causing problem in operation of the PIC. The problem is that the the PIC hangs up after sometime.
It is running fine without interrupts so it is surely the interrupts causing the problem. I was reading the datasheet and it says W_Temp should be saved in BANK0 & 1. How do you save the same variable in two banks? I also thought that since $40 location can be addressed from all banks, it was ok to just save W-Temp in that location so it can be accessed by all banks, but surely I am wrong here.
So can someone please explain this concept to me so I can correct the above code as well. Thanks
Code:
wsave var byte $40 SYSTEM ' safe for W in all banks
ssave var byte BANK0 SYSTEM ' save STATUS
fsave var byte BANK0 SYSTEM ' save FSR
ISR:
asm
movwf wsave ; Save WREG
swapf STATUS, W
clrf STATUS ; Point to bank 0
movwf ssave ; Save STATUS
movf FSR,w
movf fsave ; save FSR
; my code here
EndInt ; restore the machine state and return from interrupts
movf fsave,w
movwf FSR ; restore FSR
swapf ssave,w
movwf STATUS ; restore Status
swapf wsave,f
swapf wsave,w ; restore WREG
retfie
endasmIt is running fine without interrupts so it is surely the interrupts causing the problem. I was reading the datasheet and it says W_Temp should be saved in BANK0 & 1. How do you save the same variable in two banks? I also thought that since $40 location can be addressed from all banks, it was ok to just save W-Temp in that location so it can be accessed by all banks, but surely I am wrong here.
So can someone please explain this concept to me so I can correct the above code as well. Thanks