   NCR 77C21
   NCR 77C22
   NCR 77C22E    160pin 4MB, 1280x1024 256 col
   NCR 77C22E+   160pin
   NCR 77C32BLT  208pin BitBLT support


3C4h index  5  (R/W):  Extended Function Enable Register
bit    0  Enables extended registers if set (3C4h index >=8, 3d4h index >=30h)
       1  Reserved (always 0).
       2  If set the Hardware Configuration registers (3C4h index 23h bit 0-3,
          index 27h bit 1, index 1Fh bit 5 and index 1Eh bits 0-1) can be
          modified. On the 77c32BLT this bit causes the memory to wrap at 512K
          when set.
     3-7  Reserved

3C4h index  8  (R):  Version Number Register
bit  0-3  Chip revision
     4-7  Product Code: 0=77C22, 1=77C21, 2=77C22E (bits 0-3 <8) or 77C22E+
           (bits 0-3 >=8), 3=77c32BLT.

3C4h index 0Ah (R/W):  Cursor Color One Register
bit  0-7  Foreground color of the Bit Mapped Cursor.
          Selected if plane 0=0 and plane 1=1.

3C4h index 0Bh (R/W):  Cursor Color Zero Register
bit  0-7  Background color of the Bit Mapped Cursor.
          Selected if plane 0=0 and plane 1=0.

3C4h index 0Ch (R/W):  Cursor Control Register
bit    0  Cursor Enable. When set enables the Bit Mapped cursor.
     1-2  Cursor Height select.
          0=16 lines, 1=32 lines, 2=64 lines and 3=128 lines.
       3  Blink Frequency Select. If set the Bit Mapped Cursor is on for 16
          frames and off for another 16 frames. If clear it is on for 8 frames
          and off for another 8 frames.
       4  Blink Enable. If set the Bit Mapped Cursor blinks.
     5-6  (77c22E+,32 only) Cursor Repeat Count. Number of bytes per pixel the
          cursor passes over: 0: 1byte/pixel, 1: 2b/p, 2: 3b/p, 3: 4b/p
       7  (32 only) Cursor Width Select. If set selects a 64pixel wide cursor,
          32pixel if clear

3C4h index 0Dh (R/W):  Cursor X Location High register
bit  0-2  Bits 8-10 of the horizontal position of the Bitmapped Cursor.
          The lower 8 bits are in 3C4h index 0Eh.
     3-7  Reserved

3C4h index 0Eh (R/W):  Cursor X Location Low register
bit  0-7  Lower 8 bits of the horizontal position of the Bitmapped Cursor.
          The upper 3 bits are in 3C4h index 0Dh.

3C4h index 0Fh (R/W):  Cursor Y Location High register
bit  0-1  (22,22E) Bits 8-9 of the vertical position of the Bitmapped Cursor.
          The lower 8 bits are in 3C4h index 10h.
       2  (22E+,32) Bit 10 of the Cursor Vertical position

3C4h index 10h (R/W):  Cursor Y Location Low register
bit  0-7  Lower 8 bits of the vertical position of the Bitmapped Cursor.
          The upper 2 bits are in 3C4h index 0Fh.

3C4h index 11h (R/W):  Cursor X Index Register.
bit  0-4  (22,22E,22E+) Horizontal location of the Hot Spot from the left of
          the cursor.
     0-5  (32) Bit 5 of the Cursor X Index

3C4h index 12h (R/W):  Cursor Y Index Register.
bit  0-6  Vertical location of the Hot Spot from the top of the cursor.
       7  Reserved.

3C4h index 13h (R/W):  Cursor Storage Register High.
bit  0-7  Bits 8-15 of the address of the cursor bitmap. The lower 8 bits are
          in 3C4h index 14h.

3C4h index 14h (R/W):  Cursor Storage Register Low.
bit  0-7  Bits 0-7 of the address of the cursor bitmap. The upper 8 bits are
          in 3C4h index 13h. Must be an even address
Note: The 22E+ and 32 only documents the lower 4 bits of index 14h and doesn't
      document index 13h ??

3C4h index 15h (R/W):  Cursor Storage Offset Register High.
bit  0-7  Bits 8-15 of the Cursor Storage Offset. The lower 8 bits are in 3C4h
          index 16h.

3C4h index 16h (R/W):  Cursor Storage Offset Register Low.
bit  0-7  Bits 0-7 of the Cursor Storage Offset. The upper 8 bits are in 3C4h
          index 15h. If extended memory is enabled (3C4h index 1Eh bit4 set)
          the Cursor Storage Offset is multiplied with 16 and added to the
          Cursor Storage Address to form a 20 bit address.
Note: The cursor map is stored as a #lines*(32+32bit) bitmap
      The behavior of the cursor in each pixel is defined by the combination
      of the pixels from the two 32bit maps (The first pixel of the cursor is
      stored in the last byte):
       1st   2nd    Description
        0     0     Background color (index 0Bh)
        0     1     Foreground color (index 0Ah)
        1     0     screen data (transparent cursor)
        1     1     Inverted screen data (XOR cursor)
Note: It is possible that for the 77c22e revision 2 the pixel order in the map
      should be reversed.

3C4h index 17h (R/W):  Cursor Pixel Mask Register.
bit  0-7  Each bit set allows the corresponding bit in a pixel to be
          affected by the Bitmapped Cursor.

3C4h index 18h (R/W):  Primary Host Offset Register High.
bit  0-7  Bits 8-15 of the Primary Host Offset.
          The lower 8 bits are in 3C4h index 19h.

3C4h index 19h (R/W):  Primary Host Offset Register Low.
bit  0-7  Bits 0-7 of the Primary Host Offset. The upper 8 bits are in 3C4h
          index 18h. If extended memory is enabled (3C4h index 1Eh bit4 is
          set) all Host addresses are modified by multiplying either the
          Primary or the Secondary Host Offset with 16 and adding the result
          to the Host address.3C4h index 1Eh controls which operations use
          which Host Offset.

3C4h index 1Ah (R/W):  Display Offset Register High.                  (22,22E)
bit  0-7  Bits 8-15 of the Display Offset.
          The lower 8 bits are in 3C4h index 1Bh.

3C4h index 1Ah (R/W):  Linear Address Register 0                     (32 only)
bit  0-1  Aperture Size Select. Selects the size of the linear Aperture
               Size:  Selected by:
           0:   1M    Aperture Location 20-31
           1:   2M    Aperture Location 21-31
           2:   4M    Aperture Location 22-31
     4-7  Aperture Location Bits 20-23. Bits 20-23 of the Address of the
          linear Aperture. Bits 24-31 are in index 1Bh. Depending on the
          Aperture Size (bits 0-1) bits 20-21 of the address may not be used.

3C4h index 1Bh (R/W):  Display Offset Register Low.                   (22,22E)
bit  0-7  Bits 0-7 of the Display Offset. The upper 8 bits are in 3C4h index
          1Ah. If extended memory and Display Offset are enabled (3C4h index
          1Eh bit 4 and 3 are both set) the Display Offset is multiplied with
          16 and added to the normal display address.

3C4h index 1Bh (R/W):  Linear Address Register 1                     (32 only)
bit  0-7  Aperture Location Bits 24-31. The upper 8 bits of the Address of the
          linear Aperture. Bits 20-23 are in index 1Ah

3C4h index 1Ch (R/W):  Secondary Host Offset Register High.
bit  0-7  Bits 8-15 of the Secondary Host Offset. The lower 8 bits are in 3C4h
          index 1Dh.

3C4h index 1Dh (R/W):  Secondary Host Offset Register Low.
bit  0-7  Bits 0-7 of the Secondary Host Offset. The upper 8 bits are in 3C4h
          index 1Ch. 3C4h index 1Eh controls which operations use this
          register

3C4h index 1Eh (R/W):  Extended Memory Enable Register.
bit  0-1  DRAM Address Configuration. These bits can only be modified
          if 3C4h index 5 bit 2 is set.  0: 64Kx, 1: 256Kx, 3: 1Mx
       2  Secondary Offset Enable. If this bit and bit 4 are set all read
          operations are modified by multiplying the Secondary Host Offset by
          16 and adding the result to the host address.
       3  (22,22E only) If this bit and bit 4 are set all display addresses
          are modified by multiplying the Display Offset by 16 and adding the
          result to the normal display address.
       4  Extended Memory Enable. If set extended memory is enabled.
     5-7  (22E+,32 only) Primary/Secondary Read/Write Select.
            0:  Write to Primary, Read from Secondary
            1:  Write to Primary, Read toggles from Secondary to Primary ?
            2:  Primary at A0000h-AFFFFh, Secondary at B0000h-BFFFFh.
                Both Read/Write
            3:  Read and Write to Secondary only
            6:  (22E+ only?) Primary at A0000h-A7FFFh, Secondary at A8000h
                 -AFFFFh. Both Read/Write

3C4h index 1Fh (R/W):  Extended Clocking Mode.
bit  0-3  If bit 4 set this determines the font width:
            0   4 bit wide font
            1   7 bit wide font
            2   8 bit wide font
            3   9 bit wide font
            4  10 bit wide font
            5  11 bit wide font
            6  12 bit wide font
            7  13 bit wide font
            8  14 bit wide font
            9  15 bit wide font
           0Bh 16 bit wide font
       4  If set enables extended font width.
       5  (22E,22E+) Clock Output enable if set.
          (32 only) Clock Select Bit 2
       6  (22E,22E+) Clock Select Bit 2
          (32 only) Clock Select Bit 3
       7  Reserved

3C4h index 20h (R/W):  Extended Video Memory Addressing Register
bit    0  Addition of host address bit 16. If set (and 3CEh index 6 bits 2-3 =
          0) the range A0000h-BFFFFh can be used as one 128K window
       1  Extended chain-4 enable if set.
     2-7  Reserved.

3C4h index 21h (R/W):  Extended Pixel Control Register
bit    0  Enable graphics byte path if set. Set in extended 256color modes
       1  Enable packed/nibble pixel format (2 pixels of 4 bits per byte)
          if set.
       2  (32 only) Packed Nibble to Targa Convert Enable. If set 16bit pixel
           data stored as (Bits 0-3 Red, 4-7 Green, 8-11 Blue) (I.e. NeXT) is
           displayed as (Bits 0-4 Red, 5-9 Green, 10-14 Red) (I.e. Targa).
     4-5  Pixel Depth. The number of bytes per pixel. 0: 1-8 bits/pixel
            (1 byte), 1: 9-16b/p (2 bytes), 2: 17-24b/p (3 bytes).
     2-7  Reserved.

3C4h index 22h (R/W):  Bus Width Feed Back Register.
bit    0  (not 32) Enables 16 bit memory access if set.
       1  (not 32) Enables 16 bit I/O access if set
       2  (22E+) Select AT/MCA/CPU Interface. If bit 4 is clear, this bit is
           set for AT busses and clear for MCA busses. If bit 4 set and bit 5
           clear, this bit is set for 386DX systems, clear for 386SX systems.
          (32) AT/MCA Style Operation. If set the Video Subsystem Enable (VSE)
           register is at 46E8h (AT style), if clear at 3C3h (MCA style).
       3  (22E+) Disable CHRDY High. If set CHRDY is driven low and then
           tri-stated, if clear CHRDY is driver low and upon assertion of
           CHRDY momentarily drives it high and then tri-states it to provide
           maximum system performance.
          (32 only) Enable Palette Shadowing. If set writes to the Palette RAM
           are executed, but the LDEV/ and LRDY/ signals are not asserted,
           allowing other devices to respond to the operation
       4  (22E+) Enable CPU Bus. Set for Local Bus, clear for AT and MCA bus
          (32 only) Shadow All Writes. If set all write operations are
           executed, but the LDEV/ and LRDY/ signals are not asserted,
           allowing other devices to respond tp the operation
       5  (22E+) Select 486 Processor Interface. If bit 4 set, this bit is set
           for 486 Local bus systems with 1x clocking, clear for 386 Local Bus
           systems with 2x clocking
          (32 only) Disable All Reads. If set all register reads are ignored,
           except for port 94h, 102h, 3C3h and 46E8h
       6  (22E+) Enable 16bit BIOS if set
          (32 only) VSE Disable. If set accesses to the VSE register (46E8h
           or 3C3h) are ignored
       7  (22E+) Enable BIOS Zero Wait State. If set the ZWS signal is
           asserted during accesses to C0000h-C7FFFh, resulting in zero wait
           states
          (32 only) VSE Read Disable. If set the VSE register (46E8h or 3C3h)
           is write only

3C4h index 23h (R/W):  Performance Select Register
bit    0  (not 32) Video Memory Width Select. Set if the video memory is 32
           bit wide, clear if it is 16bit wide.
       1  (not 32) Selects 3 clock RAS cycles if set. Should not be set!!
       2  (not 22E+,32) Enables Fast Page Mode if set. Set by external
           resistor.
          (32 only) 4 Clock RAS# Precharge. If set the RAS precharge time is 4
           clocks, 3 if clear.
       3  (22E+,32) Select AT or PS/2 Style BIOS. If clear AT style operation
           is selected and mode switches between monochrome and color modes
           require the BIOS equipment flag to be updated, if clear PS/2 mode
           operation is selected and mode switches are unrestricted.
       4  (22E,22E+) Wait State Select. In ATbus systems zero wait states is
           enabled if clear. In Local Bus mode one wait state if clear, no
           wait states if set
          (32 only) Zero Wait State Select. If set RDY will be asserted in the
           first T2 of a write operation (assuming the write FIFO is not full)
           and RDY will be asserted in the second T2 cycle of a read operation
           assuming the data is not ready
       5  (22E+ only) RAS/CAS Swap. If set the RAS and CAS lines are swapped.
          Allows higher performance on Local Bus systems.
       6  (not 22E+,32) Unlatched Memory Writes (Only in 256 color modes with
          OSC3). If set limits the duration of CHRDY assertion time by
          limiting FIFO fill lengths.
       7  Latched Memory Reads. If set the assertion of CHRDY can be
          eliminated during read cycles.

3C4h index 24h (R/W):  Color Expanded Write Foreground Register.
bit  0-7  When in expanded write mode (3C4h index 26h bit 0 set) a monochrome
          bitmap can be expanded to 256 or 16 colors 8 or 16 pixels at a time.
          '1' bits in the bitmap are expanded to this color. For 16 color
          modes only bit 0-3 are used.

3C4h index 25h (R/W):  Color Expanded Write Background Register.
bit  0-7  When in expanded write mode (3C4h index 26h bit 0 set) a monochrome
          bitmap can be expanded to 256 or 16 colors 8 or 16 pixels at a time.
          '0' bits in the bitmap are expanded to this color. For 16 color
          modes only bit 0-3 are used.

3C4h index 26h (R/W):  Extended Read/Write Control Register.
bit    0  FG/BG Color Expansion Enable. When set enables expansion from
          monochrome bitmaps to full color using 3C4h index 24h and 25h as
          fore- and background colors.
       1  256Color Expansion Enable Mode 1. If set enables 256 color
          expansion. If clear 8bit pixel values can be written to the
          framebuffer as in standard mode 13h. If clear and bit 0 is set then
          16 color expansion is enabled. If set the upper 4 bits of the host
          data will be expanded to four separate pixels, each is the
          foreground color (index 24h) if the corresponding bit is set, the
          background color (index 25h) if it is clear
       2  (not 22E+,32 ?) Color Expansion Enable Mode 2. If set accesses to
           even addresses will work on the upper 4 bits of the data at the
           even address and the lower 4 bits of the data at the following odd
           address. This mode should only be used when the chip is configured
           as a 16 bit device and only with even addresses.
       3  Planar to Packed Pixel Conversion Enable. Enables 16/256 color pixel
          expansion when set. This bit should always be set when bit 1 is.
       4  Packed Pixel Mask Enable. When in packed pixel modes, this bit is
          set to enable pixel masking operations. This bit should be set when
          bit 1 is set.
       5  Packed Pixel Color Compare. When set configures the color compare
          logic to operate on packed pixel data. This bit should be set when
          bit 1 is set.
       6  Quad Word Read Latch for Writes. If set 64 bits are written when 16
          bit latched write operations occurs in write mode 1. Allows fast
          copy of data within the framebuffer.
       7  (22,22E) Address Toggle. When bit 6 is set this bit specifies
            how address information is maintained with the latched data.
          (22E+,32) Color Transparency Enable. If set the upper 4 bits of
            rotated CPU data is the Transparency mask

3C4h index 27h (R/W):  Miscellaneous Feature Select Register.
bit    0  Extended Palette addressing enable. If set I/O address bit 15 is
          passed to the RS2 pin of the palette DAC chip, so that I/O address
          03C6h - 03C9h address the first 4 registers of the DAC chip and
          83C6h - 83C9h address four other registers.
          Useful for advanced DACs with overlay and command registers.
       1  64K/256Kx16 Dual WE DRAMs. If set the 77C22E outputs DRAM interface
          signals for direct interfacing with 64K x 16 DRAMs (22E+:
          64K/256Kx16).
       2  Disable ROM BIOS CS. If set this bit disables the address decoding
          for the BIOS ROM at C000h-C7FFFh thus allowing this area to be used
          for  other adapters.
       3  User Defined Output (I/O Control pin 2). This bit is output on pin 2
          On the 32BLT this is output on pin 126
       4  (22E+,32) IRQ Drive Low. If set (or in MCA mode) the IRQ signal will
           drive low and release, if clear and in AT or Local Bus mode the IRQ
           signal will drive high and release to tristate.
       5  (22E+) Enable Output of Pixel Data. If set disables tristating of
           pixel data when EVID/ is active
          (32 only) 3C0h-3DFh Full Range Addressing. If set LRDY/ is asserted
           for any I/O access in the range 3C0h-3DFh.
       6  (22E+) Enable Output of PCLK. If set disables tristating of PCLK
           when EVID/ is active
          (32 only) Zero Wait State Read Enable. If set a zero wait read cycle
           results if the data is available from the read caches.
       7  (22E+) Enable Output of BLANK/. If set disables tristating of the
           BLANK/ signal when EVID/ is active, if clear BLANK/ is tristated
           when EVID/ is active
          (32 only) Remapped BIOS Write. If set writes to A0000h-AFFFFh are
           written to the BIOS allowing BIOS RAM updates without disabling
           BIOS shadowing and reallocation of C0000h-C7FFFh

3C4h index 28h (R/W):  Color Key Control                        (22E+,32 only)
bit    0  Enable Color Key if set
       1  Color Key Output Control. If set the Color Key Output signal goes
          active on the rising edge of PCLK, if clear on the falling edge.
     2-3  Color Key Sample Interval. Determines the sample interval of the
          pixel byte stream. The sampling begins with the first byte after
          display has been enabled. 0: Every byte, 1: Every second byte,
            2: Every third byte, 3: Every fourth byte.
     4-5  Video Delay. Controls the delay of the tristate control signal after
          a color match in number of sample intervals to delay assertion of
          the tristate control signal. 0: 0 sample intervals, 1: 1, 2: 2, 3: 3
       6  Disable Tristate Output. If set disables the tristating of PCLK and
          PIX during the color match interval, if clear PCLK and PIX will
          tristate during the color match interval
       7  (32 only) Tristate Delay Mode. If set the tristate delay specified
           in bits 4-5 are in bytes, if clear in pixels.

3C4h index 29h (R/W):  Color Key Match Value                    (22E+,32 only)
bit  0-7  The color the Color Key circuitry looks for. When a match is found
          the Color Key Match signal is asserted

3C4h index 2Ah W(R/W):  Color Key Match Value High                   (32 only)
bit 0-15  Bits 8-23 of the Color Kay Match value in index 29h

3C4h index 2Dh (R/W):  CRC Control                                 (22E+ only)
bit    0  Arm CRC Circuit. If set causes the CRC circuit to operate on video
          data for one frame (VSYNC to VSYNC). For interlaced modes two frames
          are used.
       1  If set forces the CRC value to 1. Must be reset prior to CRC testing
       2  Self Test Enable. If set no external data is used for the CRC
          generation. Intended for testing.

3C4h index 2Eh W(R):  CRC Data                                     (22E+ only)
bit 0-15  The generated CRC value.

3C4h index 30h (R/W):  Memory Mapped Register Control                (32 only)
bit    0  Enable Accelerator Control Menu (ACM). If set the ACM is enabled at
          the address specified in index 31h-33h.
       1  Enable Cursor Register Access. If set the Cursor Position registers
          (3C4h index 0Dh-10h) can be accessed at index 0Ch in the ACM.
       2  Enable Primary/Secondary Offset Register Access. If set the Primary
          and Secondary Offset registers (3C4h index 18h,19h,1Ch and 1Dh) can
          be accessed in the ACM

3C4h index 31h 3(R/W):  ACM Aperture Register 1-3                    (32 only)
bit 0-23  Bits 8-31 of the ACM Aperture address. The lower 8 bits are 0.

3C4h index 3Eh (R/W):  BIOS Utility Register 0                       (32 only)
bit  0-7  Scratch Pad
       0  Set for other HiColor DACs
       1  Set for DACs with fourth read of 3C6h = 44h (MUSIC MU9c9910)
       2  Set for DACs with fourth read of 3C6h = B3h (which ??)
       4  Appears to be the inverse of 3C4h index 22h bit 0

3C4h index 3Fh (R/W):  BIOS Utility Register 1                       (32 only)
bit  0-7  Scratch Pad

3d4h index 30h (R/W):  Extended Horizontal Timings Register.
bit    0  Horizontal Total bit 8. Bit 8 of the Horizontal Total register.
          (3d4h index 0). Bit 9 is in index 32h bit 0.
       1  Horizontal Display Enable End bit 8. Bit 8 of the Horizontal Display
          Enable End register (3d4h index 1). Bit 8 is in index 32h bit 1.
       2  Start Horizontal Blanking bit 8. Bit 8 of the Start Horizontal
          Blanking register (3d4h index 2). Bit 9 is in index 32h bit 2.
       3  Start Horizontal Retrace bit 8. Bit 8 of the Start Horizontal
          Retrace register (3d4 index 4). Bit 9 is in index 32h bit 4
       4  (22E, 22E+,32) Interlace Enable. Enables interlace video for high
           resolution graphics modes. Note in interlaced modes the line
           doubling from index 9 bits 0-4&7 is ignored. Also Line Compare
           should not be used with interlaced modes
       5  (22E+,32) Enable Extended End Bits. If set enables the extended end
           bits (index 32h bits 4-7 and index 33h bits 5-7)
       6  (22E+) CRT Clock Divide by Two. If set the video clock is divided
           by 2.
Note: The extended Function Enable Register (3C4h index 5) bit 0 must be 1 to
      access this register.

3d4h index 31h (R/W):  Extended Start Address Register
bit  0-3  Display Start Address bit 16-19. (bit 0-15 are in 3d4h index Ch and
          Dh).
       4  Bit 8 of Address Row Offset. Bit 8 of the CRTC Offset (3d4h index
          13h).

3d4h index 32h (R/W):  Extended Horizontal Timings Two Register     (22E+, 32)
bit    0  Horizontal Total Bit 9. Bit 9 of the Horizontal Total register (3d4h
          index 0). Bit 8 is in index 30h bit 0
       1  Horizontal Display Enable End bit 9. Bit 9 of the Horizontal Display
          End register (3d4h index 1). Bit 8 is in index 30h bit 1
       2  Horizontal Blank Start bit 9. Bit 9 of the Start Horizontal Blanking
          register (3d4h index 2). Bit 8 is in index 30h bit 2.
       3  Horizontal Retrace Start bit 9. Bit 9 of the Start Horizontal
          Retrace register (3d4h index 0). Bit 8 is in index 30h bit 3.
     4-5  Horizontal Blank End bits 6-7. Bits 6-7 of the Horizontal Blanking
          End register (3d4h index 3).
     6-7  Horizontal Retrace End bits 5-6. Bits 5-6 of the Horizontal Retrace
          register (3d4h index 5).

3d4h index 33h (R/W):  Extended Vertical Timings                   (22E+ only)
bit    0  Vertical Total bit 10.  Bit 10 of the Vertical Total register (3d4h
          index 6). Bits 8 and 9 are in 3d4h index 7 bits 0 and 5.
       1  Vertical Display Enable End bit 10. Bit 10 of the Vertical Display
          End register (3d4h index 12h). Bits 8 and 9 are in 3d4h index 7 bits
          1 and 6
       2  Vertical Blank Start bit 10. Bit 10 of the Vertical Blank Start
          register (3d4h index 15h). Bit 8 is in 3d4h index 7 bit 3 and bit 9
          in 3d4h index 9 bit 5
       3  Vertical Retrace Start bit 10. Bit 10 of the Vertical Retrace Start
          register (3d4h index 10h). Bits 8 and 9 are in 3d4h index 7 bits 2
          and 7
       4  Line Compare bit 10. Bit 10 of the Line Compare register (3d4h index
          18h). Bit 8 is in 3d4h index 7 bit 4 and bit 9 in 3d4h index 9 bit 6
     5-6  Vertical Blank End bits 8-9. Bits 8-9 of the Vertical Blank End
          register (3d4h index 16h).
       7  Vertical Retrace End bit 4. Bit 4 of the Vertical Retrace End
          register. Bits 0-3 are in 3d4h index 11h bits 0-3.

3d4h index 34h (R/W):  Monitor Power Management                      (32 only)
bit    0  Set HSync low
       1  Set HSync high
       2  Set VSync low
       3  Set VSync high


The Memory Mapped Registers (Accelerator Control Menu - ACM) can only be
accessed when 3C4h index 30h bit 0 is set. The base address of the ACM
registers are defined in 3C4h index 31h-33h.

Memory 00h W(R/W):  Primary Offset                                   (32 only)
bit 0-15  If 3C4h index 30h bit 2 is set this is the Primary Host Offset
          register (3C4h index 18h-19h)

Memory 04h W(R/W):  Secondary Offset                                 (32 only)
bit 0-15  If 3C4h index 30h bit 2 is set this is the Primary Host Offset
          register (3C4h index 1Ch-1Dh)

Memory 09h (R/W):  Mode Control Register                             (32 only)
bit  0-1  DRAM Address Configuration. These bits can only be modified
          if 3C4h index 5 bit 2 is set.  0: 64Kx, 1: 256Kx, 3: 1Mx
       2  Secondary Offset Enable. If this bit and bit 4 are set all read
          operations are modified by multiplying the Secondary Host Offset by
          16 and adding the result to the host address.
       4  Extended Memory Enable. If set extended memory is enabled.
     5-7  Primary/Secondary Read/Write Select.
            0:  Write to Primary, Read from Secondary
            1:  Write to Primary, Read toggles from Secondary to Primary ?
            2:  Primary at A0000h-AFFFFh, Secondary at B0000h-BFFFFh.
                Both Read/Write
            3:  Read and Write to Secondary only
Note: This is the Extended Memory Enable register (3C4h index 1Eh).

Memory 0Ch W(R/W):  Cursor X Position Register                       (32 only)
bit 0-10  If 3C4h index 30h bit 1 is set this is the Cursor X Position
          registers (3C4h index 0Dh and 0Eh)

Memory 0Eh W(R/W):  Cursor Y Position Register                       (32 only)
bit 0-11  If 3C4h index 30h bit 1 is set this is the Cursor Y Position
          registers (3C4h index 0Fh and 10h)

Memory 30h (R/W):  BLT Start Register                                (32 only)
bit    0  Start/Stop. Set to start a BLT operation, clear to stop the
          current operation
       1  Text BLT. Set for Text Mode BLTs, clear for standard BLTs
       2  BLT Completed Interrupt. If set causes an interrupt when the
          Accelerator engine has completed an operation. The interrupt is
          cleared when a 0 is written to this bit.
       3  Write FIFO Empty Interrupt. If set enables an interrupt when the
          Write FIFO goes empty

Memory 32h (R):  BLT Status Register                                 (32 only)
bit    0  Ready. If clear the engine is busy, if set the operation has
          finished and the parameters can be updated.
       1  Error. If set indicates that an illegal BLT operation was entered.
          This bit is cleared when a new operation is started.
       2  BLT Done Interrupt Status. Set when an interrupt has been generated
          due to a BLT Done condition.
       3  Write FIFO Near Empty Interrupt. Set if an interrupt has been
          generated due to a Write FIFO Near Empty condition.
       4  Write FIFO Full. Set when the Write FIFO is full

Memory 34h W(R/W):  BLT Control Register                             (32 only)
bit    1  Color Compare Invert. If clear color match operations return 1 for
          the pixels which match the reference color and 0 for those that
          don't, if set this is reversed.
       3  Map Width. If set the data transferred when either the Source or
          Destination data is in system memory is padded or truncated to
          achieve word aligned data.
       4  Large Pattern Enable. If clear 8x8 pixel patterns are used, if set
          16x16 patterns are used for 256 color modes.
       5  Transparency Enable. If set enables background transparency for
          color expand operations.
       6  Vertical Direction. The Blit direction is "down" (increasing Y) if
          set, "up" (decreasing Y) if clear
       7  Horizontal Direction. The Blit direction is "left" (increasing X) if
          set, "right" (decreasing X) if clear.
       9  Color Fill Enable. If set the operation is a solid fill and only one
          pixel of the pattern data need be read.
      10  Color Compare Enabled if set
      11  Color Expand Enable. If set the source data is monochrome and is
          replaced with fore/background data in the full color depth
      12  Destination Address Mode. If set the source data is stored in
          linear format, if clear it is stored in rectangular format.
      13  Source Address Mode. If set the destination data is stored in
          linear format, if clear it is stored in rectangular format.
      14  Destination Location. If set the Destination is in the frame
          buffer, if clear the destination data is transferred to the system
          memory via the ?read? FIFO.
      15  Source Location. If set the Source data comes from the frame buffer,
          if clear the system supplies the Source data

Memory 38h (R/W):  Pattern X Rotation                                (32 only)
bit  0-3  The Horizontal Pixel alignment of the pattern

Memory 39h (R/W):  Pattern Y Rotation                                (32 only)
bit  0-3  The Vertical Pixel alignment of the pattern

Memory 3Ah (R/W):  Raster Opcode                                     (32 only)
bit  0-7  The raster opcode. See MS-Windows trinary raster codes for the full
          list. CCh is copy source -> Destination

Memory 3Ch W(R/W):  Bitmap Dimension Width                           (32 only)
bit 0-11  Bitmap Width. The width of the Source and Destination bitmaps in
          pixels

Memory 3Eh W(R/W):  Bitmap Dimension Height                          (32 only)
bit 0-11  Bitmap Height. The height of the Source and Destination bitmaps in
          pixels. For Text BLTs this is the character cell height

Memory 40h D(R/W):  Destination Register                             (32 only)
bit  0-2  Bit position for monochome bitmaps. For Color Compare to Memory BLTs
          this field specifies the initial bit alignment of the Destination
          bitmap
    3-24  Destination Address. This is the address of the starting corner of
          the Destination Bitmap

Memory 44 D(R/W):  Source Register                                   (32 only)
bit  0-2  Bit position for monochome bitmaps. For Color Expand BLTs this field
          specifies the initial bit alignment of the Source bitmap
    3-24  Source Address. This is the address of the starting corner of the
          Destination Bitmap

Memory 48h D(R/W):  Pattern Register                                 (32 only)
bit  0-2  Bit offset, must be 0
    3-24  Pattern Address. This is the address of the starting corner of
          the Pattern. The address must be DWORD aligned.

Memory 4Ch D(R/W):  Foreground Color Register                        (32 only)
bit 0-23  The foreground color

Memory 50h D(R/W):  Background Color Register                        (32 only)
bit 0-23  The Background Color.


  ID NCR VGA:

  if testinx2($3C4,5,5) then
  begin
    wrinx($3C4,5,0);   {Lock extensions}
    if not testinx($3C4,$10) then
    begin
      wrinx($3C4,5,1);
      if testinx($3C4,$10) then
        case rdinx($3C4,8) div 16 of
          0:NCR 77C22;
          1:NCR 77C21;
          2:if (rdinx($3C4,8) and 15)<8 then NCR 77C22E
                                        else NCR 77C22E+;
          3:NCR 77c32BLT;
        end;
    end;
  end;


  Video Modes:

  40h G 1600 1200  16  PL4                    32BLT
  41h G 1600 1200 256  P8                     32BLT
  50h G  640  480 16m  P24                    32BLT
  51h G  800  600 16m  P24                    32BLT
  54h T  132   50  16  (8x8)
  55h T  132   25  16  (8x16)
  56h T  132   50   4  (8x8)
  57h T  132   25   4  (8x16)
  58h G  800  600  16  PL4
  59h G  800  600   2
  5Ah G 1024  768   2
  5Bh G 1024  768  16  PL4    (Interlaced)
  5Ch G  800  600 256  P8
  5Dh G 1024  768  16  PL4
  5Eh G  640  400 256  P8
  5Fh G  640  480 256  P8
  61h G 1024  768 256  P8     (Interlaced)    22E !!
  62h G 1024  768 256  P8                     22E !!
  67h G 1280 1024  16  PL4    (Interlaced)    22E !!
  6Ah G 1280 1024 256  P8     (Interlaced)    22E !!
  6Bh G 1280  960 256  P8                     22E !!
  6Ch G 1280 1024  16  PL4                    32BLT
  70h G  640  480 32k  P15                    22E !!
  71h G  800  600 32k  P15                    22E
  72h G 1024  768 32k  P15                    32BLT
  78h G  640  480 64k  P16                    22E
  79h G  800  600 64k  P16                    22E
  7Ah G 1024  768 64k  P16                    32BLT

Note: Modes above 57h may require a driver (setmode.sys) to be loaded
      depending on BIOS version.
