[Coco] Coco 3 Missing Mystery Color Mode

[Steve Ostrom]

----- Original Message ----- 
From: "brian palmer" <tigers2roar at yahoo.com.au>
To: <coco at maltedmedia.com>
Sent: Tuesday, April 27, 2010 12:47 AM
Subject: [Coco] Coco 3 Missing Mystery Color Mode


> Hi Steve.
>
> Can you tell us what 1989 issue of Coco-Link this article was in. And what 
> Page it is on thanks. I have 4 issues of 89 coco-link but none seem to 
> have anything about this article you mentioned.
>
> laters
>
> Briza
>

Briza, this article, titled Coco Real Time Clock by Ken Wagnitz, was in 
Coco-Link vol. 2, No.3 from June 1989 and starts on page 25.  Here are some 
of the more relevent quotes:

     Browsing through the circuit diagram for the Coco3, I discovered that 
the PIA outputs which control the display modes of the Video Display chip 
(6847) of the Coco2, are not connected to anything in the Coco3!  Being of a 
suspicious nature, I even checked the board in my Coco3 to confirm this 
terrific fact.
     It is true.  There are unused outputs there for us hackers.  So I wired 
up my clock circuit directly to that PIA, using the `unused` PIA port pins. 
It worked fine.
...
     He reported that my Basic clock-read program mucked up the screen on 
his Coco3.  On further questioning, I find out that the same happens when he 
boots OS9.
...
     It turns out that although the PIA outputs are not connected to the 
GIME chip on the Coco3 (which handles the display), the GIME responds to 
writes to the PIA as if it was connected!

-- Steve --