  GENOA SuperVGA Chips.

    Genoa 5100/5200  Tseng ET3000 chips 256 Kbytes
          5300/5400  Tseng ET3000 chips 512 Kbytes
          6100       Own chip 256 Kbytes ??
          6200/6300  Own chip 256 Kbytes   max  800x600/16 or 640x400/256
          6400/6600  Own chip 512 Kbytes   max 1024x768/16 or 800x600/256

          6600 is the 6400 for MicroChannel
          64/6600A support 70Hz refresh rate.

          7900 is Tseng ET4000 based with SS24 DAC.
          New 7000 series appears to be Tseng 4000 based.



3C3h (R/W):  Global Enable PS/2 Register
bit   0  VGA Microchannel enabled if set

3C4h index  5  (R/W):  Configuration Register
bit   0  (R) PC/AT if set, PS/2 else
      1  (R) 8bit bus if set, 16bit else
      2  (R) 8bit ROM if set, 16bit else
      3  Reserved
      4  (R) I/O address 3xx if set, 2xx else
    5-6  ROM BIOS size:
          0: 24kb ROM
          1: 30kb ROM
          2: 32kb ROM
          3:  0kb ROM
      7  8 simultaneous fonts if set, 2 else

3C4h index  6  (R/W):  Memory Segment Register
bit 0-2  Read bank no.
    3-5  Write bank no.
      6  If clear use 3C2h bit 5 as A16 rather than bit 0/3 of this register.

3C4h index  7  (R/W):  Enhanced Control #2
bit   0  External Clock select bit 2. Bits 0-1 are in 3C2h/3CCh bits 2-3.
      1  Allow frequencies above 50MHz
      2  16 bit video memory access if set
      3  VGA on Motherboard if set, Card else
      4  Reserved
      5  TTL monitor if set, Analog else
      6  Non-Maskable Interrupts Enabled if set
      7  Reserved

3C4h index  8  (R/W):  Enhanced Control #3
bit   0  MDA,Hercules or CGA emulation if set
      1  MonoChrome Autoswitch if set. Causes NMI if 3B8h is written to
      2  Color Autoswitch if set. Causes NMI if 3D8h is written to
      3  EGA operation if set, VGA else
      4  60Hz Vertical if set, 70Hz else
      5  Enable flicker free function
      6  Enable extended memory addressing
      7  Enable 1024x768 addressing

3C4h index 10h (R/W):  Enhanced Control #4
bit   0  Fast Scroll if set
      1  Fast Decode if set
      2  Enables 2 bank access if set
      3  Pre_Wait enabled if set
    4-5  Reserved
      6  Fast Write enabled if set
      7  Select memory bank 0 or 1

3CEh index  9  (R/W):  Enhanced Control #5
bit   6  If set Access even pixels in plane 0/1 and odd pixels in plane 2/3.
         (Mode 7Fh)
      7  If set Display even pixels from plane 0/1 and odd pixels from plane
         2/3. (Mode 7Fh)

3CEh index 0Ah (R/W):  Program Status Register 1
bit 0-7  Scratch

3CEh index 0Bh (R/W):  Program Status Register 2
bit 0-7  Scratch

3d4h index 2Eh (R/W):  Herchi Register
bit   0  If set Maximum Scan Line Register (3d4h index 9) is programmable in
         CGA modes
      1  Enables Chinese applications in Hercules mode if set
    2-7  Reserved

3d4h index 2Fh (R/W):  Interlace Control Register
bit   0  Interlace active if set
      1  Enable Quadword addressing mode
      2  Select Character Clock as memory addressing counter clock
      3  Interlaced Graphics/Alpha mode
    4-7  Reserved

46E8h (R): Global Enable PC/AT Register
bit 3  Adapter VGA enabled if set



  Bank select:

    Separate read and write banks are selected through 3C4 index 6.


  Memory locations:

  $C000:$37  2 bytes   start of info table from start of ROM
                       Usually $C000:$B4

  $C000:x    1 byte    $77
  $C000:x+1  1 byte    Version.
                        $00 Genoa 6200 or 6300
                        $11 Genoa 6400 or 6600
                        $22 Genoa 6100
                        $33 Genoa 5100 or 5200   (Tseng 3000)
                        $55 Genoa 5300 or 5400   (Tseng 3000)

  $C000:x+2  2 bytes   $6699


  ID Genoa Chip Set:

  ad:=memw[$C000:$37];
  if (mem[$C000:ad]=$77) and (memw[$C000:ad+2]=$6699) then
    case mem[$C000:ad+1] of
    $33,$55:TSENG 3000 chips with special modes;
        $22:GENOA_6100
          0:GENOA_6200 or GENOA_6300
        $11:GENOA_6400 or GENOA_6600
    end;

Note that this would also ID the UMC 85c408 as a GENOA 6400, so test for UMC
first


  Video Modes:

    The Genoa 5xxx series boards use Tseng modes.


    The 6xxx series boards use the following modes:

  40h  T    80   25    2         SuperEGA BIOS 3.0+
  41h  G   720  348    2         SuperEGA BIOS 3.0+  at B000h
  42h  G   720  348    2         SuperEGA BIOS 3.0+  at B800h

  43h  T    80   29    2  (9x12)
  44h  T    80   32    2  (9x11)
  45h  T    80   44    2  (9x8)
  46h  T   132   25    2  (8/9x14)
  47h  T   132   29    2  (8/9x12)
  48h  T   132   32    2  (8/9x11)
  49h  T   132   44    2  (8/9x8)
  58h  T    80   32   16  (9x16)
  59h  G   720  512   16  PL4
  5Ah  T   100   42?  16
  5Bh  G   640  350  256  P8
  5Ch  G   640  480  256  P8
  5Dh  G   720  512  256  P8
  5Eh  G   800  600  256  P8
  5Fh  G  1024  768   16  PL4
  60h  T   132   25   16  (8x14)
  61h  T   132   29   16  (8x8)
  62h  T   132   32   16  (8x11)
  63h  T   132   44   16  (8x8)
  64h  T   132   60   16  (8x8)
  6Ah  G   800  600   16  PL4
  6Bh  T   100   75   16
  6Ch  G   800  600  256  P8
  72h  T    80   60   16
  73h  G   640  480   16  Pl4
  74h  T    80   66   16  (8x8)
  75h  G   640  528   16  PL4      SuperEGA BIOS 3.0+
  76h  T    94   29       (8x14)   SuperEGA BIOS 3.0+
  77h  G   752  410   16  PL4      SuperEGA BIOS 3.0+
  78h  T   100   75   16
  79h  G   800  600   16  PL4
  7Ah  T   114   60       (8x8)    SuperEGA BIOS 3.0+
  7Bh  G   912  480   16  PL4      SuperEGA BIOS 3.0+
  7Ch  G   512  512   16  PL4
  7Dh  G   512  512  256  P8
  7Eh  G   640  400  256  P8
  7Fh  G  1024  768    4  PL2

     Mode 7Fh: 1024x768 4 color
       2 bits per pixel planar mode
       Even pixels are in planes 0 and 1, odd pixels are in planes 2 and 3.


BIOS Extensions:
----------1010F0-----------------------
INT 10 - Genoa 7900 Set 24bit mode
        AX = 10F0h
        BL = 3Eh

        Sets 640 x 480 16M color mode.
Return: AX = 0010h if successful
----------1010F0-----------------------
INT 10 - Genoa 7900 - Get DAC Type
        AX = 10F1h
Return: AX = 0010h
        BX = 0000h     Normal VGA DAC          16/256  colors
           = 0001h     HiColor 5/5/5 format    16/256/32K  colors
           = 0002h     HiColor 5/6/5 format    16/256/32K/64K  colors
           = 0602h     Special New DAC         16/256/32K/64K/256K  colors
           = 0802h     Special New DAC         16/256/32K/64K/16M  colors

Note:  *Genoa's MultimediaVGA Model 7900 will return BX = 0802H
        (8/8/8 format capability) and Model 7900sx will return
         BX = 0602H (6/6/6 format capability).
Note:  The one Genoa 7900 I've seen returns BX = 0803h.
