[Coco] Coco 2 6847T1 test program

mike at borncoco.com mike at borncoco.com
Wed Jul 19 10:33:59 EDT 2017

Hi Ron,
I don't know of a specific test for the T1. While you can use a simple poke to get true lower case, it causes issues unless you move ROM to RAM. ADOS supports the true lower option and that code may be helpful to look at as well. 
Here's a link to a good discussion about enabling true lowercase and potential pitfalls.
[ http://thread.gmane.org/gmane.comp.hardware.tandy.coco/67991 ]( http://thread.gmane.org/gmane.comp.hardware.tandy.coco/67991 )
I also found this from Robert Gault: 
If you look at the specs for the 6847 video chip, you will see that it contains a set of ascii characters that are all upper case, normal or inverted. You either need an external ROM with new characters or a different video chip (6847T1) to get true lower case letters. Tandy did not use true lower case even if the newer chip was present.
If you look at the source code for Extended Basic 2.0 (Coco3), you will see
$95C5 lda $FF22
anda #7 prevent lower case in text mode
sta $FF22
The above turns off true lower case and forces inverted text so even the Coco3 does not use true lower case on the low res text screen.
With a Coco3 you can change the 7 to a $57 and send $50 to $FF22 to get true lower case. That is also true for some stock Coco2 models if you move the ROM code to RAM.
-Mike Rowen
-----Original Message-----
From: "Ron Klein" <ron at kdomain.org>
Sent: Wednesday, July 19, 2017 9:17am
To: "CoCoList for Color Computer Enthusiasts" <coco at maltedmedia.com>
Subject: [Coco] Coco 2 6847T1 test program

Hello everyone,

Is there a test program available that can detect whether or not you have a
6847T1 in a Coco 2? If a 6847T1 is detected, can it enable the lowercase
fonts (until the unit is turned off)?


Coco mailing list
Coco at maltedmedia.com

More information about the Coco mailing list