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.



       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 of a 3bit field).
             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  Ah (R/W): Program Status Register 1
       bit 0-7  Scratch

       3CEh index  Bh (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:

    Seperate 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:

    if (meml[$c000:mem[$c000:$37]] and $ffff00ff)=$66990077 then
      case mem[$c000:mem[$c000:$37]+1] of
        $33,$55:TSENG 3000 chips with special modes;
      else GENOA_VGA !!!


  ID Genoa Chip Revision:

    Case mem[$c000:mem[$c000:$37]+1] of
      $22:GENOA_6100
        0:GENOA_6200 or GENOA_6300
      $11:GENOA_6400 or GENOA_6600
    end;


  Video Modes:

    The Genoa 5xxx series boards use Tseng modes.


    The 6xxx series boards use the following modes:

    43h  T    80   29    2
    44h  T    80   32    2
    45h  T    80   44    2
    46h  T   132   25    2
    47h  T   132   29    2
    48h  T   132   32    2
    49h  T   132   44    2
    58h  T    80   32   16
    59h  G   720  512   16 
    5Ah  T   100   42?  16
    5Bh  G   640  350  256 packed
    5Ch  G   640  480  256 packed
    5Dh  G   720  512  256 packed
    5Eh  G   800  600  256 packed
    5Fh  G  1024  768   16 planar
    60h  T   132   25   16
    61h  T   132   29   16
    62h  T   132   32   16
    63h  T   132   44   16
    64h  T   132   60   16
    6Ah  G   800  600   16 planar
    6Bh  T   100   75   16
    6Ch  G   800  600  256 packed   
    72h  T    80   60   16
    73h  G   640  480   16 planar
    74h  T    80   66   16
    78h  T   100   75   16
    79h  G   800  600   16 planar
    7Dh  G   512  512  256 packed
    7Eh  G   640  400  256 packed
    7Fh  G  1024  768    4 planar

     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.