Funny you should ask.  This one bit me this weekend... 

First, to define W_Temp in bank 1, just add 0x80 to the first location, so 
also define the same var (change the name slightly to something like W_TEMP1) 
in location 0xA0.  That "mirrors" it in bank 1.  Fig 2-4 on the 16F87x 
datasheer will help.

Here's the part that bit me, so I'll save you some grief just in case...

On other 16F PICs (such as the 16F874), there is a small data-RAM section that 
is shared/accessible in all the other banks, but that section on the 
16F873/F874 is not completely shared in the other banks.  Ex: locations 
0x70-0x7F is not accessible in bank 1.  Since I ported code over from a 
16F872, I still had the original context-saving routine at the start of the 
ISR, but had to modify it to explicitly save W in bank 0.  Example 12-1 on 
the 16F87x datasheet shows this as the 3rd instruction ("CLRF   STATUS") to 
switch back to bank 0 before saving W.

Cost me a few hours of very manual debugging before I realized this. :-(

Cheers,
-Neil.


On Monday 13 June 2005 11:02 am, Francois Robbertze scribbled:
> "For the PIC16F873/874 devices, the register W_TEMP must be defined in both
> banks 0 and 1 and must be defined at the same offset from the bank base
> address (i.e., If W_TEMP is defined at 0x20 in bank 0, it must also be
> defined at 0xA0 in bank 1). The registers, PCLATH_TEMP and STATUS_TEMP, are
> only defined in bank 0."
>
> To define W_TEMP in bank 0 is easy:
>
> W_TEMP                equ    0x20
> STATUS_TEMP    equ    0x21
>
> How do one define W_TEMP in bank _1 again?
>
> regards
>
> Francois


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