I have made an interesting discovery.
My program only contains two lines that change the bank select bit RP1.
This means that my PBP program can only be accessing the first two RAM banks which is only a little more than half that the chip provides.
It seems I will have to change the RP1 bit manualy in assembler to use the rest of the RAM. Surely I'm not the only one who has encountered this?
... well it seems I answered my own question.
A little later I have found out that some of the exixting asm in my PBP code
that addresses RAM does so incorrectly when PBP changes the location of
that RAm without my asm code knowing about it.
So a little thing like:
@ incfsz _colcnt,f
@ goto _decpnt
can cause the whole program to break when the variable 'colcnt' requires
a change tot he bank select bits in order to address it. or at least that's what
I think is happening at the moment...
Anyway I have solved my original problem
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