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