Copyright(C) 1994,1995,1996,1997 Terumasa KODAKA, Takeshi KONO
■Multimedia architecture control
Subject           PC-98GS
Explanation     o PC-98GS is equipped with its own graphics system. This graphics system is named Multimedia Architecture.
                o Whether the multimedia architecture can be used is indicated by 0000:0458h bit 6 in the system common area.
                o The I/O ports used by the multimedia architecture are as follows.
                  --------------+-------+-----+-----------------------------------------
                  I/O address   | Width | R/W | Content
                  --------------+-------+-----+-----------------------------------------
                  A46Eh         | BYTE  |  R  | Various status acquisition
                  A560h         | BYTE  | R/W | SGP work RAM access mode
                  A562h         | BYTE  | R/W | Unknown
                  A564h         | BYTE  | R/W | Address projected to VRAM window #0
                  A566h         | BYTE  | R/W | Address projected to VRAM window #1
                  A568h         | BYTE  |     | Unknown
                  A56Ah         | BYTE  |     | Unknown
                  A56Ch         | BYTE  |  R  | SGP status
                  A56Eh         | BYTE  | R/W | Unknown (SGP related)
                  A660h         | BYTE  | R/W | Synchronous mode setting
                  A662h         | BYTE  | R/W | Screen mode setting
                  A664h         | BYTE  | R/W | Screen horizontal expansion mode specification
                  A666h         | BYTE  | R/W | Screen vertical expansion mode specification
                  A668h         | BYTE  |  R  | Status acquisition
                  A760h         | BYTE  | R/W | Pallet number specification
                  A762h         | BYTE  | R/W | Brightness setting (green)
                  A764h         | BYTE  | R/W | Brightness setting (red)
                  A766h         | BYTE  | R/W | Brightness setting (blue)
                  A76Ah         | BYTE  |     | Unknown
                  A76Ch         | BYTE  | R/W | Palette set selection
                  A76Eh         | BYTE  | R/W | AT bit specification
                  A860h         | WORD  | R/W | Compose specification
                  A862h         | WORD  | R/W | Compose specification
                  A864h         | BYTE  | R/W | Transparent color mode setting
                  A866h         | BYTE  | R/W | Frame #0 Transparent color palette number
                  A868h         | BYTE  | R/W | Frame #1 Transparent color palette number
                  A86Ah         | BYTE  | R/W | Frame #2 transparent color palette setting
                  A86Ch         | BYTE  | R/W | Frame #3 transparent color palette setting
                  A960h         | BYTE  | R/W | Transparent color mode specification for video screen
                  A962h         | WORD  | R/W | Blue component upper level specification
                  A964h         | WORD  | R/W | Blue component lower level specification
                  A966h         | WORD  | R/W | Red component upper level specification
                  A968h         | WORD  | R/W | Red component lower level specification
                  A96Ah         | WORD  | R/W | Green component upper level specification
                  A96Ch         | WORD  | R/W | Green component lower level specification
                  AA60h         | BYTE  | R/W | Mask slot designation
                  AA62h         | WORD  | R/W | X coordinate (dot) of mask area start position (left end)
                  AA64h         | WORD  | R/W | X coordinate (dot) of mask area end position (right end)
                  AA66h         | BYTE  | R/W | Y coordinate (dot) of mask area start position (top end)
                  AA68h         | BYTE  | R/W | Y coordinate (dot) of mask area end position (bottom edge)
                  AA6Ch         | BYTE  | R/W | Blue component of background color
                  AA6Dh         | BYTE  | R/W | Red component of background color
                  AA6Eh         | BYTE  | R/W | Green component of background color
                  AB60h         | BYTE  | R/W | Top priority screen blue fade level
                  AB64h         | BYTE  | R/W | Top priority screen red fade level
                  AB68h         | BYTE  | R/W | Top priority screen green fade level
                  AB62h         | BYTE  | R/W | 2nd priority screen blue fade level
                  AB66h         | BYTE  | R/W | 2nd priority screen red fade level
                  AB6Ah         | BYTE  | R/W | 2nd priority screen green fade level
                  AB6Ch         | BYTE  | R/W | Display color quantization state
                  AB6Dh         | BYTE  |     | Unknown
                  AB6Eh         | BYTE  | R/W | Special effect specification
                  AB6Fh         | BYTE  | R/W | Unknown
                  AC60h         | BYTE  | R/W | Effect range color mode specification
                  AC62h         | BYTE  | R/W | Effect range color specification
                  AC64h         | BYTE  | R/W | Top priority screen designation
                  AC65h         | BYTE  | R/W | Next priority screen specification
                  AC6Eh         | BYTE  |     | Unknown
                  AD60h         | WORD  | R/W | X-OFFSET of frame #0
                  AD62h         | WORD  | R/W | Y-OFFSET of frame #0
                  AD64h         | WORD  | R/W | Display start line of frame #0
                  AD66h         | WORD  | R/W | Number of display lines for frame #0
                  AD68h         | WORD  | R/W | X-OFFSET of frame #1
                  AD6Ah         | WORD  | R/W | Y-OFFSET of frame #1
                  AD6Ch         | WORD  | R/W | Frame #1 display start line
                  AD6Eh         | WORD  | R/W | Number of display lines for frame #1
                  AE60h         | WORD  | R/W | X-OFFSET of frame #2
                  AE62h         | WORD  | R/W | Y-OFFSET of frame #2
                  AE64h         | WORD  | R/W | Frame #2 display start line
                  AE66h         | WORD  | R/W | Number of display lines for frame #2
                  AE68h         | WORD  | R/W | X-OFFSET of frame #3
                  AE6Ah         | WORD  | R/W | Y-OFFSET of frame #3
                  AE6Ch         | WORD  | R/W | Frame #3 display start line
                  AE6Eh         | WORD  | R/W | Number of display lines for frame #3
                  AF60~AF66h   | BYTE  |     | Unknown
                  AF68h         | BYTE  |     | Unknown
                  AF6C~AF6Fh   | BYTE  |     | Unknown
                  --------------+-------+-----+-----------------------------------------
Relation          0000:0458h bit 6
I/O               A46Eh
Name              Get various statuses
                  Undocumented
Function
                  [READ]
                  bit 7:B bank EMS
                          1=EMS mapping state (OUT 43Fh,22h)
                          0=VRAM mapping state (OUT 43Fh,20h)
                  bit 6:GS graphic mode state
                          1=GS graphic ON state (OUT 6Ah,0Fh)
                          0=GS graphics OFF state (OUT 6Ah, 0Eh)
                  bit 5: Extended graphics mode state
                         1=256 color mode state (OUT 6Ah, 21h)
                         0=16 color mode state (OUT 6Ah, 20h)
                  bit 4 to 0: Not available Use
                  [WRITE] Unknown
Explanation     o Indicates the status of the current graphic mode, etc.
Relation          I/O 006Ah - 0Eh,0Fh
                  I/O 006Ah - 20h,21h
                  I/O 043Fh - 20h,22h
I/O               A560h
Name              SGP Work RAM Access Mode
Undocumented
Function
                  [READ/WRITE]
                  bit 7: SGP work RAM access
                         1=permitted
                         0=prohibited bit
                  6 to 2: Unused (?)
                  bit 1,0: SGP work RAM bank
                           00b=BANK#0
                           01b=BANK#1
                           10b=BANK#2
                           11b=BANK#3
Explanation     o Control access to SGP work RAM
Relation          INT 1Fh - Function 00h
                  INT 1Fh - Function 01h A800:0000~7FFFh
I/O               A562h
Name              Unknown
Undocumented
Function          [READ/WRITE]
                  bit 7~0:Unknown
Explanation     o Details unknown
I/O               A564h,A566h
Name              Window #0,#1 bank number setting
Function
                  --------------+-------+-----+------------------------------------
                  I/O address   | Width | R/W | Content
                  --------------+-------+-----+------------------------------------
                  A564h         | BYTE  | R/W | Address projected to VRAM window #0
                  A566h         | BYTE  | R/W | Address projected to VRAM window #1
                  --------------+-------+-----+------------------------------------
Explanation     o Set the VRAM address to be projected to B0000~B7FFFh, B8000~BFFFFh in 4KB units.
Relation          B000:0000~7FFFh B800:0000~7FFFh
I/O               A568h,A56Ah
Name              Unknown
Undocumented
Function
                  Unknown
Explanation     o Details unknown
I/O               A56Ch
Name              SGP Status
Undocumented
Function
                  [READ]
                  bit 7~1:Unknown
                  bit 0:BUSY
                        1=BUSY
                        0=READY
Explanation     o Get the status of SGP(SuperGraphicProcessor).
                o Details unknown
Relation          I/O A56Eh
I/O               A56Eh
Name              Unknown
Undocumented
Function
                  [READ/WRITE]
                  bit 7~0:Unknown
Explanation     o Details unknown (SGP related)
Relation          I/O A56Ch
I/O               A660h
Name              Synchronization mode setting
Undocumented
Function
                  [READ/WRITE]
                  bit 7: Digitize
                         1=Yes
                         0=No
                  bit 6,5: Not used?
                  bit 4: Unknown
                  bit 3: Unknown
                  bit 2~0: Unknown
Explanation     o Configure various settings related to synchronization signals. Details unknown.
I/O               A662h
Name              Screen mode settings (pixel size and resolution settings for each frame)
Undocumented
Function
                  [READ/WRITE]
                  bit 7: 16.77 million color frame buffer mode
                         1=Special frame buffer
                         0=Normal frame buffer
                  bit 6: Not used
                  bit 5: Number of frame #2 colors
                         1=65536 colors
                         0=256 colors
                  bit 4: Frame #0,#1 line number setting
                         1=640x512x1
                         0=640x256x2
                  bit 3: Not used?
                  bit 2: Frame #0,1 and #2,3 concatenation mode
                         1=Concatenate frames #0 to #3
                         0=Frame #0,1 and #2,3
                  bit 1: Number of colors in frame #0
                         1=16M/65536 colors
                         0=256 colors
                  bit 0: Number of lines in frame #0, #1 setting
			 1=640x512x1
			 0=640x256x2
Explanation     o Set the number of colors, resolution, etc. for each frame.
I/O               A664h
Name              Screen horizontal expansion mode specification
Undocumented
Function
                  [READ/WRITE]
                  bit 3: FRAME#3 2x horizontal enlargement
                  bit 2: FRAME#2 2x horizontal enlargement
                  bit 1: FRAME#1 2x horizontal enlargement
                  bit 0: FRAME#0 2x horizontal enlargement
                         1=Yes
                         0=not
Function        o Specify the frame to display twice horizontally enlarged.
Relation          I/O A666h
 
I/O               A666h
Name              Screen vertical expansion mode specification
Undocumented
Function
                  [READ/WRITE]
                  bit 3: FRAME#3 2x vertical enlargement
                  bit 2: FRAME#2 2x vertical enlargement
                  bit 1: FRAME#1 2x vertical enlargement
                  bit 0: FRAME#0 2x vertical enlargement
                         1=Yes
                         0=not
Explanation     o Specify the frame to display twice vertically enlarged.
Relation          I/O A664h
I/O               A668h
Name              Get Status
Undocumented
Function
                  [READ]
                  bit 7~5: Unknown
                  bit 4: VSYNC
                         1=Generating
                         0=Not occurring
                  bit 3~0: Unknown
Explanation     o Details unknown
Relation
I/O               A760h, A762h, A764h, A766h
Name              Palette Settings
Undocumented
Function
                  ------------------------+-------+-----+----------------------------
                  I/O address             | Width | R/W | Content
                  ------------------------+-------+-----+----------------------------
                  A760h                   | BYTE  | R/W | Pallet number specification
                  A762h                   | BYTE  | R/W | Brightness setting (green)
                  A764h                   | BYTE  | R/W | Brightness setting (red)
                  A766h                   | BYTE  | R/W | Brightness setting (blue)
                  ------------------------+-------+-----+----------------------------
Explanation     o Set the palette. Valid only on 256 color screens.
                o After specifying the palette number with I/O A760h, set its brightness.
Relation          A76Ch
I/O               A76Ah
Name              Unknown
Undocumented
Function          Unknown
Explanation     o Details unknown
I/O A76Ch
Name              Palette set selection
Undocumented
Function
                  [READ/WRITE]
                  bit 7 to 5: Unused?
                  bit 4: Palette mode selection
                         1=24bit palette mode
                         0=16bit palette mode
                  bit 3,2: Unused?
                  bit 1,0: Palette set selection
                           11b=Palette set #3 selection
                           10b=Palette set #2 selection
                           01b=Palette set #1 selection
                           00b=Palette set #0 selection
Explanation     o Specify the palette set to be set with I/O ports A760h, A762h, A764h, and A766h.
                o When using a 24-bit palette, you cannot use more than 3 frames.
Relation          I/O A760h
I/O               A76Eh
Name              AT bit specification
Undocumented
Function
                  [READ/WRITE]
                  bit 7~3: Unused (set to 0)
                  bit 2~0: AT bit setting
                           100b=AT bit is set to G0
                           010b=AT bit is set to R0
                           001b=AT bit is set to B0
                           Any other combination is prohibited.
Explanation     o In PC-98GS, when 65536 pixels are used, 5 bits are allocated to the brightness of blue, red, and green.
                  The remaining 1 bit (AT bit) can be set as the least significant bit of either blue, red, or green.
                  Set where to allocate the AT bit for this I/O port.
I/O               A860h
Name              Compose specification
Undocumented
Function
                  [READ/WRITE]
                  bit 15: Screen display for priority #3
                          1=Yes
                          0=No
                  bit 14-12: Screen specification for priority #3
                             110b=Video screen
                             101b=Screen 3
                             100b=Screen 2
                             011b=Screen 1
                             010b=Screen 0
                             001b=Current screen
                             000b=Not specified
                  bit 11: Screen display of priority #2
                          1=Yes
                          0=No
                  bit 10~8: Screen specification of priority #2
                            110b=Video screen
                            101b=Screen 3
                            100b=Screen 2
                            011b=Screen 1
                            010b=Screen 0
                            001b=Current screen
                            000b=Not specified
                  bit 7: Screen display with priority #1
                         1=Yes
                         0=No
                  bit 6 to 4: Screen specification with priority #1
                              110b=Video screen
                              101b=Screen 3
                              100b=Screen 2
                              011b=Screen 1
                              010b=Screen 0
                              001b=Current screen
                              000b=Not specified
                  bit 3: Screen display with priority #0
                         1=Yes
                         0=No
                  bit 2~0: Screen specification with priority #0
                            110b=Video screen
                            101b=Screen 3
                            100b=Screen 2
                            011b=Screen 1
                            010b=Screen 0
                            001b=Current screen
                            000b=Not specified
Explanation     o Specify the source to be displayed for each priority on the screen.
Relation          I/O A862h
I/O               A862h
Name              Compose specification
Undocumented
Function
                  [READ/WRITE]
                  bit 15 to 9: Not used
                  bit 8: Text top priority flag
                         1=Text has top priority
                         0=Text is integrated with graphics
                  bit 7: Screen display with priority #5
                         1=Yes
                         0=No
                  bit 6 to 4: Screen specification for priority #5
                              110b=Video screen
                              101b=Screen 3 100b=Screen 2
                              011b=Screen 1
                              010b=Screen 0
                              001b=Current screen
                              000b=Not specified
                  bit 3: Screen display for priority #4
                         1=Yes
                         0=No
                  Bit 2~0: Screen specification for priority #4
                           110b=Video screen
                           101b=Screen 3
                           100b=Screen 2
                           011b=Screen 1
                           010b=Screen 0
                           001b=Current screen 000b=No specification
Explanation     o Specify the source to be displayed for each priority on the screen.
                o If you specify the bit8 text highest priority flag, 98 graphics screens will always be given the highest priority.
Relation          I/O A860h
I/O A864h
Name              Transparent color mode setting
Undocumented
Function
                  [READ/WRITE]
                  bit 7,6: Frame #3 transparent color mode specification
                  bit 5,4: Frame #2 transparent color mode specification
                  bit 3,2: Frame #1 transparent color mode specification
                  bit 1,0: Frame #0 Transparent color mode specification
                           11b=Other than setting value
                           10b=Setting value only
                           01b=Palette specification larger than setting value
                           00b=Less than setting value
Explanation     o Set which transparent color mode to use for each frame.
                o Transparent colors are only available on 256 color screens.
Relation          I/O A866h
I/O               A866h, A868h, A86Ah
Name              Transparent color palette settings
Undocumented
Function
                  ------------+-------+-----+-------------------------------------------
                  I/O address | Width | R/W | Content
                  ------------+-------+-----+-------------------------------------------
                  A866h       | BYTE  | R/W | Frame #0 Transparent color palette number
                  A868h       | BYTE  | R/W | Frame #1 Transparent color palette number
                  A86Ah       | BYTE  | R/W | Frame #2 transparent color palette setting
                  A86Ch       | BYTE  | R/W | Frame #3 transparent color palette setting
                  ------------+-------+-----+-------------------------------------------
Explanation     o Specify the palette number used to specify transparent color for each frame.
Relation          I/O A864h
I/O               A960h
Name              Transparent color mode specification for video screen
Undocumented
Function
                  [READ/WRITE]
                  bit 7~2: Not used
                  bit 1: Frame #2 transparent color flag
                  bit 0: Frame #0 transparent color flag
                         0=Transparent color available
                         1=No transparent color
Explanation     o Set the transparency color for the video screen.
Relation          I/O A962~A96Dh
I/O               A962h
Name              Blue component upper level specification
Undocumented
Function
                  [READ/WRITE]
                  bit 15 to 8: Specify the blue upper level of frame #2
                  bit 7 to 0: Specify the blue upper level of frame #0
Explanation     o Specify the upper limit of the brightness signal (blue) of the image displayed in frames #0 and 2.
Relation          I/O A964h
I/O               A964h
Name              Blue component lower level specification
Undocumented
Function
                  [READ/WRITE]
                  bit 15 to 8: Specify the blue lower level of frame #2
                  bit 7 to 0: Specify the blue lower level of frame #0
Explanation     o Specify the lower limit of the luminance signal (blue) of the image displayed in frames #0 and 2.
Relation          I/O A962h
I/O               A966h
Name              Red component upper level specification
Undocumented
Function
                  [READ/WRITE]
                  bit 15 to 8: Specifies the red upper level of frame #2
                  bit 7 to 0: Specifies the red upper level of frame #0
Explanation     o Specify the upper limit of the brightness signal (red) of the image displayed in frames #0 and 2.
Relation          I/O A968h
I/O               A968h
Name              Red component lower level specification
Undocumented
Function
                  [READ/WRITE]
                  bit 15 to 8: Specify the red lower level of frame #2
                  bit 7 to 0: Specify the red lower level of frame #0
Explanation     o Specify the lower limit of the brightness signal (red) of the image displayed in frames #0 and 2.
Relation          I/O A966h
I/O               A96Ah
Name              Green component upper level specification
Undocumented
Function
                  [READ/WRITE]
                  bit 15 to 8: Specify the green upper level of frame #2
                  bit 7 to 0: Specify the green upper level of frame #0
Explanation     o Specify the upper limit of the brightness signal (green) of the image displayed in frames #0 and 2.
Relation          I/O A96Ch
I/O               A96Ch
Name              Green component lower level specification Undocumented
Function
                  [READ/WRITE]
                  bit 15 to 8: Specify the green lower level of frame #2
                  Bit 7 to 0: Specify the green lower level of frame #0
Explanation     o Specify the lower limit of the luminance signal (green) of the image displayed in frames #0 and 2.
Relation          I/O A96Ah
I/O               AA60h
Name              Mask slot specification
Undocumented
Function
                  [READ/WRITE]
                  bit 7: Mask setting
                         1=Mask enabled
                         0=Mask prohibited
                  bit 6: Mask area specification
                         1=Mask outside the area
                         0=Mask inside area
                  bit 5: 5th slot specification
                  bit 4: 4th slot specification
                  bit 3: 3rd slot specification
                  bit 2: 2nd slot specification
                  bit 1: 1st slot specification
                  bit 0: 0th slot specification
                         1=Mask
                         0=Do not mask
Explanation     o Set the mask insertion position and type.
Relation          I/O AA22~AA69h
I/O               AA62h, AA64h, AA66h, AA68h
Name              Mask position specification
Undocumented
Function
                  ------------+-------+-----+-----------------------------------------------------------
                  I/O address | Width | R/W | Content
                  ------------+-------+-----+-----------------------------------------------------------
                  AA62h       | WORD  | R/W | X coordinate (dot) of mask area start position (left end)
                  AA64h       | WORD  | R/W | X coordinate (dot) of mask area end position (right end)
                  AA66h       | BYTE  | R/W | Y coordinate (dot) of mask area start position (top end)
                  AA68h       | BYTE  | R/W | Y coordinate (dot) of mask area end position (bottom edge)
                  ------------+-------+-----+-----------------------------------------------------------
Explanation     o Specify the position of the mask area.
I/O               AA6Ch, AA6Dh, AA6Eh
Name              Background color specification
Undocumented
Function
                  ------------+-------+-----+-----------------------------------------------------------
                  I/O address | Width | R/W | Content
                  ------------+-------+-----+-----------------------------------------------------------
                  AA6Ch       | BYTE  | R/W | Blue component of background color
                  AA6Dh       | BYTE  | R/W | Red component of background color
                  AA6Eh       | BYTE  | R/W | Green component of background color
                  ------------+-------+-----+-----------------------------------------------------------
Explanation     o Specify the background color
I/O               AB60h, AB64h, AB68h
Name              Top priority screen fade level
Undocumented
Function
                  ------------+-------+-----+-----------------------------------------------------------
                  I/O address | Width | R/W | Content
                  ------------+-------+-----+-----------------------------------------------------------
                  AB60h       | BYTE  | R/W | Top priority screen blue fade level
                  AB64h       | BYTE  | R/W | Top priority screen red fade level
                  AB68h       | BYTE  | R/W | Top priority screen green fade level
                  ------------+-------+-----+-----------------------------------------------------------
Explanation     o Set the fade level of the top priority screen.
I/O               AB62h, AB66h, AB6Ah
Name              2nd priority screen fade level
Undocumented
Function
                  ------------+-------+-----+-----------------------------------------------------------
                  I/O address | Width | R/W | Content
                  ------------+-------+-----+-----------------------------------------------------------
                  AB62h       | BYTE  | R/W | 2nd priority screen blue fade level
                  AB66h       | BYTE  | R/W | 2nd priority screen red fade level
                  AB6Ah       | BYTE  | R/W | 2nd priority screen green fade level
                  ------------+-------+-----+-----------------------------------------------------------
Explanation     o Set the fade level of the top priority screen.
I/O               AB6Ch
Name              Display color quantization state
Undocumented
Function
                  [READ/WRITE]
                  bit 7~0:Unknown
Explanation     o Details unknown
I/O               AB6Dh
Name              Unknown
Undocumented
Function
                  Unknown
Explanation     o Details unknown
I/O               AB6Eh
Name              Special effect specification
Undocumented
Function
                  [READ/WRITE]
                  bit 7~0: Special effect mode
                            0000xxxxb=Special effects prohibited
                            0011xxxxb=Transparent composition
                            0101xxxxb=Additive composition
                            0110xxxxb=Filter processing
                            0111xxxxb=Transparent processing
                            01000000b=All bits OFF (display becomes black)
                            01000001b=not(A or B)
                            01000010b=not(A) and B
                            01000011b=not(A)
                            01000100b=A and not(B)
                            01000101b=not(B)
                            01000110b=A xor B
                            01000111b=not(A and B)
                            01001000b=A and B
                            01001001b=not(A xor B)
                            01001010b=B
                            01001011b=not(A) or B
                            01001100b=A
                            01001101b=not(B) or A
                            01001110b=A or B
                            01001111b=All bits ON (display becomes white)
Explanation     o Specify special effects such as logical operations between screens
Relation          I/O AB6Fh
I/O               AB6Fh
Name              Unknown
Undocumented
Function
                  [READ/WRITE]
                  bit 7~2: Unused?
                  bit 1: Special effect start
                  bit 0: Fade related
                         00b=Unknown
                         01b=Unknown
                         10b=Unknown
                         11b=Fade in progress
Explanation     o Details unknown
Relation          I/O AB6Eh
I/O               AC60h
Name              Effect range color mode specification
Undocumented
Function
                  [READ/WRITE]
                  bit 7~0: Effect range color mode specification
                            00h=Less than the set color
                            01h=Above the set color
                            02h=Only the set color
                            03h=Other than the set color
Explanation     o Specify the color range for special effects.
                o Valid only when the highest priority frame specified by I/O port AC64h is 8 bits/pixel.
Relation          I/O AB6Eh
                  I/O AB6Fh
                  I/O AC62h
                  I/O AC64h
I/O               AC62h
Name              Effect range color specification
Undocumented
Function
                  [READ/WRITE]
                  bit 7~0: Effect range color
Explanation     o Set the color used to specify the color range for special effects.
                o Valid only when the highest priority frame specified by I/O port AC64h is 8 bits/pixel.
Relation          I/O AC60h
                  I/O AC64h
I/O               AC64h
Name              Top priority screen designation
Undocumented
Function
                  [READ/WRITE]
                  bit 7: Special effect flag
                         1=Special effect set
                         0=Special effect not set
                  bit 6~2: Not used? bit 1,0: Top priority screen designation
                           11b=Frame #3
                           10b=Frame #2
                           01b=Frame #1
                           00b=Frame #0
Function        o Specify the screen for setting special effects
Relation          I/O AC60h
                  I/O AC62h
                  I/O AC65h
I/O               AC65h
Name              Next priority screen specification
Undocumented
Function
                  [READ/WRITE]
                  bit 7: Unused (set to 0)
                  bit 6: Background surface
                  bit 5: Video screen
                  bit 4: 98 Graphics screen
                  bit 3: Frame 3
                  bit 2: Frame 2
                  bit 1: Frame 1
                  bit 0: Frame 0
                         0=Do not use
                         1=Use
Explanation     o Specify the next priority screen.
Relation          I/O AC64h
I/O               AC6Eh
Name              Unknown
Undocumented
Function
                  Unknown
Explanation     o Details unknown
I/O               AD60h, AD62h, AD64h, AD66h
Name              Frame #0 display position setting
Undocumented
Function
                  ------------+-------+-----+-------------------------------------
                  I/O address | Width | R/W | Content
                  ------------+-------+-----+-------------------------------------
                  AD60h       | WORD  | R/W | X-OFFSET of frame #0
                  AD62h       | WORD  | R/W | Y-OFFSET of frame #0
                  AD64h       | WORD  | R/W | Display start line of frame #0
                  AD66h       | WORD  | R/W | Number of display lines for frame #0
                  ------------+-------+-----+-------------------------------------
Explanation     o Set the display position of frame #0
I/O               AD68h, AD6Ah, AD6Ch, AD6Eh
Name              Frame #1 display position setting
Undocumented
Function
                  ------------+-------+-----+-------------------------------------
                  I/O address | Width | R/W | Content
                  ------------+-------+-----+-------------------------------------
                  AD68h       | WORD  | R/W | X-OFFSET of frame #1
                  AD6Ah       | WORD  | R/W | Y-OFFSET of frame #1
                  AD6Ch       | WORD  | R/W | Frame #1 display start line
                  AD6Eh       | WORD  | R/W | Number of display lines for frame #1
                  ------------+-------+-----+-------------------------------------
Explanation     o Set the display position of frame #1
I/O               AE60h, AE62h, AE64h, AE66h
Name              Frame #2 display position setting
Undocumented
Function
                  ------------+-------+-----+-------------------------------------
                  I/O address | Width | R/W | Content
                  ------------+-------+-----+-------------------------------------
                  AE60h       | WORD  | R/W | X-OFFSET of frame #2
                  AE62h       | WORD  | R/W | Y-OFFSET of frame #2
                  AE64h       | WORD  | R/W | Frame #2 display start line
                  AE66h       | WORD  | R/W | Number of display lines for frame #2
                  ------------+-------+-----+-------------------------------------
Explanation     o Set the display position of frame #2
I/O               AE68h, AE6Ah, AE6Ch, AE6Eh
Name              Frame #3 display position setting
Undocumented
Function
                  ------------+-------+-----+-------------------------------------
                  I/O address | Width | R/W | Content
                  ------------+-------+-----+-------------------------------------
                  AE68h       | WORD  | R/W | X-OFFSET of frame #3
                  AE6Ah       | WORD  | R/W | Y-OFFSET of frame #3
                  AE6Ch       | WORD  | R/W | Frame #3 display start line
                  AE6Eh       | WORD  | R/W | Number of display lines for frame #3
                  ------------+-------+-----+-------------------------------------
Explanation     o Set the display position of frame #3
I/O               AF60~AF66h,AF68h,AF6C~AF6Fh
Name              Unknown
Undocumented
Function
                  Unknown
Explanation     o Details unknown