[Coco] CoCo I/O Ports

Gene Heskett gene.heskett at verizon.net
Thu Nov 15 23:39:27 EST 2007

On Thursday 15 November 2007, Steve Bjork wrote:
>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.)

That's a WordPack-RS, a text only video card.  It can be run in parallel with 
the usual gime video modes, independently.  So you can run two monitors at 
the same time.  The gime video is pure white when the keyboard focus is on 
the WP-RS.  You could start an assembly on a gime screen, and list the 
listing file on the amber screen & watch the whole thing on both screens. 
There were at least 2 variations and IIRC the eprom which contained the 
character pattern data was slightly different between the two that I had.  
I'd also fiddled with some of the init data removing the blank space at the 
sides and top & bottom so the display, whose dot clock was locked at 4x 
subcarrier, would fill a 13" amber monitor.  That ran the monitor at around 
18.5 khz horizontal and about 70 hz vertical, but it ran that way for a 
decade with no ill effects on the monitor.

>>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

Cheers, Gene
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