[Coco] Re: Re: [Color Computer] Re: Adapter from Coo3 to SVGA
kevdig at hypersurf.com
Wed Apr 6 13:57:45 EDT 2005
jdaggett at gate.net wrote:
> Here is a better explanation.
> When you write to $FF22 you will write to the GIME chip i nternal register at $FF22.
> Internal to the GIME this register is a write only register. So that the old Coco1/2 bits
> for mode control of the 6847 will be maintained. A read of that address address will
> actually read from the PIA chip.
> Thus PB3 to PB7 of the PIA chip can actually be used as general purpose inputs
> only. I was in error when I said that they could be used as general purpose I/O (input
> and/or output).
Didn't the PIAs in the unis and deuces use sloppy decoding. An entire
32 byte block was assigned when only 4 are needed. Didn't they just
repeat? i.e. $ff24-$ff27 == $ff20-$ff23? Does the GIME also do this? If
not could we just use $ff24-$ff27 for output?
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