[Coco] Coco 2 6847T1 test program

[Ron Klein]

Hi Simon and Mike,

Thanks for all the info (and links, too)!  It's extremely helpful!

-Ron


On Wed, Jul 19, 2017 at 10:10 AM, Simon Jonassen <simon at roust-it.dk> wrote:

> 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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