  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 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:

    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]=$77) and (mem[$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;


  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
    7Ch  G   512  512   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.


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

