💾 Archived View for uscoffings.net › retro-computing › systems › Tandy › oldskool › whichvid.txt captured on 2023-07-10 at 15:14:20.
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20-May-89
Fm: Frank O'Donnell 75006,3573
I'm writing MS-DOS graphics software that recognizes the IBM-type machine
identification byte at F000:FFFE and, if the machine's an IBM PCjr, adapts the
video mode taking into account the "special" video modes available on the jr.
I understand the Tandy 1000 machines have graphics modes like the jr. Since I
don't have much familiarity with Tandys, I'm wondering ... (a) Do they also
have a unique ID signature byte at F000:FFFE, or some other way of
distinguishing models? (b) Is there somewhere easy to get a rundown of the
video modes on these models (basically just a list of mode #, resolution and
colors)?
Fm: Bryan Headley/Tandy VDS 70007,2060
Frank,
The method to follow is this: check for EGA, VGA, Hercules... If these
all fail, and you assume CGA, then check for Tandy 1000.
At F000:FFFE you'll find an FF hex (PC's machine ID).
Then, check F000:C000, where, if it is a 1000, you'll find an 21 Hex.
DO THE CHECK IN THE ORDER SHOWN ABOVE.
Tandy does not warrant that AT's, PS/2's, etc., do not have a 21 Hex
at F000:C000, only PC's.
Video Modes supported by BIOS:
0 40x25 BW text
1 40x25 color
text 2 80x25 BW
text 3 80x25 color
text 4 320x200 color graphics (CGA compatible)
5 320x200 BW graphics with 4 shades (CGA compatible)
6 640x200 BW graphics with 2 shades (CGA compatible)
7 Reserved
8 160x200 color graphics with 16 colors (TGA/PCjr)
9 320x200 color graphics with 16 colors (TGA/PCjr)
A 640x200 color graphics with 4 colors (TGA/PCjr)
Colors supported by Tandy 1000:
In 4-color mode:
For BL=0 in Set Color Palette (AH=11 dec)
0 = black, 1 = green, 2 = red, 3 = yellow For BL=1 in Set Color Palette
0 = black, 1 = cyan, 2 = magenta, 3 = white
In 16-color mode:
0 = black, 1 = blue, 2 = green, 3 = cyan, 4 = red, 5 = magenta,
6 = yellow, 7 = light gray, 8 = dark gray, 9 = light blue,
10 = light green, 11 = light cyan, 12 = light red,
13 = light magenta, 14 = yellow, 15 = white
Good luck!
Bryan