Posted By
Csabo
on 2022-01-26
08:43:49
|  Re: Change screen address
You are correct that $FF14 controls the location of the text screen. Unfortunately AFAIK you cannot change where the KERNAL writes characters. Just to be absolutely clear, are you thinking something like this?
LDA #$18
STA $FF14 ; change text screen location from the default $0800 to $1800
LDA #$01
JSR $FFD2 ; output letter "A" to the screen
And then you'd want the letter to appear somewhere from $1C00-$1FE7? Unfortunately the KERNAL uses a fixed lookup table that points to the screen (from $D802/$D81B), which will always point to the $0C00 area.
I could be wrong?... If so I hope someone enlightens me, but I've never seen this work on Plus/4.
Therefore I'd say you have 3 options:
1) sidestep the entire issue by rearranging your code so that the text screen is at the default location (no need for any KERNAL changes)
2) copy the ROM to RAM and change what needs to be changed (you do lose half the free memory, but might be the least amount of trouble)
3) write your own character input/output routines.
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