[Coco] [ColorComputer] VDG Detection

[Alex Evans]

Thank you very much.

On Sun, Dec 21, 2025 at 7:19 PM Michael Pittsley via Coco <
coco at maltedmedia.com> wrote:

> I ran on Coco3 stock and CoCo 3 with Gime-x both returned 00263
> Then I ran on CoCo 1 then CoCo 2 without T1, then with T1 and then with
> CoCoVGA all returned 00262.
>
>
> Michael Pittsley
> ________________________________
> From: ColorComputer at groups.io <ColorComputer at groups.io> on behalf of Alex
> Evans via groups.io <varmfskii=gmail.com at groups.io>
> Sent: Sunday, December 21, 2025 10:05 AM
> To: colorcomputer at groups.io <colorcomputer at groups.io>; CoCoList for Color
> Computer Enthusiasts <coco at maltedmedia.com>
> Subject: [ColorComputer] VDG Detection
>
> In the ROM Diagnostics thread, there is the question of whether or not it
> is possible to detect through software whether an MC6847 or an MC6847T1 was
> present. An idea was presented that there may be a difference in the bumper
> of lines per frame. I came up with some code to test this possibility, but
> I only have access to a machine with an MC6847. I have managed to get a
> null result using xroar (in both cases 262 for NTSC and 312 for PAL). If
> there's anyone is willing to post results from actual hardware to confirm
> this null result is accurate, it would be greatly appreciated.
>
> Attached you will find the source code for the test as well as DECB and
> DragonDOS binaries.
>
> Thank you.
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