You understand this correctly: you must allocate W_TEMP at the same offset
in both banks for this to work.

Bob Ammerman
RAm Systems
(contract development of high performance, high function, low-level
software)

----- Original Message -----
From: "Drew Vassallo" <snurple@HOTMAIL.COM>
To: <PICLIST@MITVMA.MIT.EDU>
Sent: Sunday, June 24, 2001 7:10 PM
Subject: [PIC]: Context saving in ISRs


> Ok, so I'm switching from the 16C71 to the 16C715.  No big deal.  The
major
> hangup is that I can't ignore Bank switching anymore, since the bank 0 RAM
> isn't mapped in bank 1.  Again, no biggie.  BUT...
>
> Is it my imagination, or is this poor information from Microchip:
>
> (from the 16C71x datasheet, including C71 and C715)
>
> EXAMPLE 8-1: SAVING STATUS AND W REGISTERS IN RAM
>
> MOVWF W_TEMP ;Copy W to TEMP register, could be bank one or zero
> SWAPF STATUS,W ;Swap status to be saved into W
> MOVWF STATUS_TEMP ;Save status to bank zero STATUS_TEMP register
> :
> :(ISR)
> :
> SWAPF STATUS_TEMP,W ;Swap STATUS_TEMP register into W
> ;(sets bank to original state)
> MOVWF STATUS ;Move W into STATUS register
> SWAPF W_TEMP,F ;Swap W_TEMP
> SWAPF W_TEMP,W ;Swap W_TEMP into W
>
>
> I believe this is where my program is taking a dump.  The first line,
"could
> be in bank 1 or zero" is totally wrong.  The W_TEMP variable *MUST* by in
> *BOTH* banks 0 and 1, to allow for either case when an interrupt is
> serviced.
>
> Am I going crazy, or is this not true?  The datasheet says NOTHING MORE
> about how to perform context saving.  Note that when the variables are
> restored, the original Bank is selected prior to restoring W, which is
fine,
> *IF* you have W_TEMP available in both banks.
>
> Please slap me into reality if I'm wrong here.
>
> --Andrew
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