[Coco] CoCo 3 display offset question.

[William Astle]

jdaggett at gate.net wrote:
> Phil the GIME chip sees the complete 512K memory map. In the Coco compatible mode, 
> bit#7 of the INIT0 register($FF90) is set then the GIME chip will respond to data plugged 
> into the registers at $FFC6 to $FFD3. Then the GIME chip will only see the upper 64K of the 
> 512K memory map from what I understand. 

Not quite true. In "Coco compatible mode", the vertical offset registers
are interpreted differently. The BASIC ROM sets them so that the "base
offset" for the old SAM registers is the top 64K. However, with
sufficient twiddling, you can still set the display on any 8 byte
boundary. There's a formula for how it works in the "Super Extended
Basic Unravelled" book.

-- 
William Astle
finger lost at l-w.net for further information

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