[Coco] CoCo 32k rom architecture

[Robert Gault]

Barry Nelson wrote:
> Sorry, but that article talks in great detail about designs for a 64k and 128k program pak, but only briefly mentions the 32k paks, which use a different system. I am not interested in breaking the 32k barrier at this time I am just interested in reaching it and in the workings of the standard 32k paks for the CoCo 3 and the format or the .ccc files for these paks. The larger ones can wait for now. I need to understand how the .ccc file layout is ordered, how the rom chip is ordered, and how the 32k mode is activated. Also on my mind is if the 32k paks use the SLENB line to control the bus and allow access to the extra memory space?
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$FF90 should give the Coco3 access to 32K External ROM by settings bits 0-1 high.
So the code ought to be:
  orcc #$50
  lda #%01000111
  sta $FF90
  access the external ROM
  lda #%01000100
  sta $FF90
  andcc #$AF

If you want external ROM always ON, don't restore $FF90.

Robert