[Coco] Coco 2 6847T1 test program

[Simon Jonassen]

Hey Guys,

theres a few ways you can test for a t1 vdg, just using BASIC

10 poke &hff22,64
20 goto 20

that will give you a green border with text still on the screen if it's a T1

if you *fiddle* a little with that you can get an orange border/background

10 poke &hff22,64+8
20 goto 20

the following will give you some lowercase chars on the first line:

10 for i=0 to 255
20 poke &h400+I,i
30 next
40 poke &hff22,16
50 goto 50

NOTICE that all of these snippets go off into an endless loop as BASIC will nuke the values in $ff22 back to standard otherwise !!!

you can combine the 64,16,8 to get say lowercase with orange border and background !


/Simon :-)





-----Oprindelig meddelelse-----
Fra: Coco [mailto:coco-bounces at maltedmedia.com] På vegne af mike at borncoco.com
Sendt: 19. juli 2017 16:34
Til: CoCoList for Color Computer Enthusiasts
Emne: Re: [Coco] Coco 2 6847T1 test program


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 [code:1:b6fee96998]
$95C5 lda $FF22
anda #7 prevent lower case in text mode
sta $FF22
[/code:1:b6fee96998]
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.
 
Cheers,
-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)?

Thanks!

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