Re: Stashing data at $ff00-$ff04 in 128 mode?

From: eyethian (
Date: 2001-07-27 02:39:35

----- Original Message -----
From: "Marko Mäkelä" <>
> Oh, now I got it: you use the zero page or stack page relocation register
> and write the data to $100-$104 or to $00-$04 (well, I guess it's easier
> for you to write to $100 or $101 than to $00 or $01 (I've done the latter
> without using the MMU)).

I like the idea. I was wondering if the zero page relocation register would
work for $00 and $01 of the $ff00/$ff01 registers? According to my Mapping
the C128, all references to $00 and $01 would go to the true $00/$01 of the
8502's I/O ports. I think that the following code would not work:

lda #value
sta $00    ; sta $ff00
lda #value
sta $01    ; sta $ff01

But, would the following code work?

ldx #$01
lda #value
sta $ff,x    ; sta $ff00
lda #value
sta $ff,x    ; sta $ff01

By indirectly accessing $00 and $01 using the wraparound feature of the 65xx
CPU, would this method work with a relocated zero page in a C128 system?

If that doesn't work, then the relocatable stack should work in accessing
the ram underneath $ff00-$ff04.

-Todd Elliott

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