[Coco] CoCo I/O Ports

Steve Bjork 6809er at bjork-huffman.net
Thu Nov 15 20:17:44 EST 2007

At 04:48 PM 11/15/2007, you wrote:

>The WP-RS I had came out of the box using $ff76-77-78-79
>But since that wipes out 8 addresses in the usual 4 address wide scheme, it
>wasn't much to move it to $ff74-77 and fix the driver since it was the 12
>upper addresses I moved below.  Spare gate on the card.

What is a WP-RS?  (It has been a long time since I used most of the 
CoCo acronyms.)

>What we've needed for decades is a quick kit to isolate the $FF00-03 from
>$FF04-1F, ditto for the $FF20-03 range, leaving $FF24-3F open for our uses.
>Cheers, Gene

The only problem is too many assembly coders use the mirror addresses 
to save cycles when talking to the PIA chips. (I was not one of 
them.) It has been a problem since day one of CoCo programming. That 
is why the CoCo 3 kept the same address (with mirrors) all the old 
CoCo 1/2 I/O ports.

Steve (6809er) Bjork

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