┌──────────────────────────────────────────────────┐
│ Programming the Chips And Technologies SVGA Chip │
└──────────────────────────────────────────────────┘
Written for the PC-GPE by Mark Feldman
e-mail address : u914097@student.canberra.edu.au
myndale@cairo.anu.edu.au
Please read the file SVGINTRO.TXT
(Graphics/SVGA/Intro PC-GPE menu option)
┌───────────────────────────────────────────┐
│ THIS FILE MAY NOT BE DISTRIBUTED │
│ SEPARATE TO THE ENTIRE PC-GPE COLLECTION. │
└───────────────────────────────────────────┘
┌────────────┬───────────────────────────────────────────────────────────────
│ Disclaimer │
└────────────┘
I assume no responsibility whatsoever for any effect that this file, the
information contained therein or the use thereof has on you, your sanity,
computer, spouse, children, pets or anything else related to you or your
existance. No warranty is provided nor implied with this information.
┌────────────┬───────────────────────────────────────────────────────────────
│ Setup mode │
└────────────┘
To modify some of the CAT's internal SVGA registers the card must be placed
into setup mode. This is done by writing the value 1Eh to port 46E8h. To
exit setup mode write the value 0Eh to port 46E8h.
┌─────────────────────┬──────────────────────────────────────────────────────
│ Enabling Extensions │
└─────────────────────┘
The CAT's extended registers are normally locked and must be enabled before
you attempt to modify them. To enable them, you must enter setup mode,
write the value 80h to port 103h and exit setup mode. To disable them
you must enter setup mode, write the value 00h to port 103h and exit
setup mode.
┌──────────────────────────┬─────────────────────────────────────────────────
│ Identifying the CAT Chip │
└──────────────────────────┘
Detecting the presence of a CAT chip can be done by entering setup mode,
checking that the value returned from reading port 104h is A5h and then
exiting setup mode.
┌────────────────────────────────────────────────┬───────────────────────────
│ Identifying which CAT Chip and Revision Number │
└────────────────────────────────────────────────┘
The CAT chip type and revision number can be determined by enabling
extensions, reading the value of register 0 and disabling extensions.
The top 4 bits (4-7) are the chip id and the lower 4 are the version
number.
┌───────────────────────────────┐
│ Chip ID Chip │
├───────────────────────────────┤
│ 1 82c451 or 82c452 │
│ 2 82c455 │
│ 3 82c453 │
│ 5 82c456 │
└───────────────────────────────┘
The 82c451 and 82c452 can be distinguished by attempting to modify
register 3Ah (Graphics Cursor Color 1, make sure you set it back to what it
was). If the register exists the chip is an 82c452.
Alternatively the chip ID can be determined using the Get Controller
Information BIOS call (see below).
┌────────────────────────────┬───────────────────────────────────────────────
│ CAT Graphics Display Modes │
└────────────────────────────┘
┌───────────────────────────────────────────────────┐
│ Mode Resolution Colors Chip │
├───────────────────────────────────────────────────┤
│ 25h 640x480 16 451/452/453 │
│ 6Ah 800x600 16 451/452/453 │
│ 70h 800x600 16 451/452/453 │
│ 71h 960x720 16 452 │
│ 72h 1024x768 16 452/453 │
│ 78h 640x400 256 451/452/453 │
│ 79h 640x480 256 452/453 │
│ 7Ah 768x576 256 452 │
│ 7Ch 800x600 256 453 │
│ 7Eh 1024x768 256 453 │
└───────────────────────────────────────────────────┘
┌────────────────────────┬───────────────────────────────────────────────────
│ The CAT Display Memory │
└────────────────────────┘
The following registers can only be modified while the extended registers
are enabled (See Enabling Extensions above).
The 451, 455 and 456 are always in single-paging mode and have 4 64K
banks. To switch to a bank you must first enable access to extended memory
with the following procedure:
Port[$3D6] := $0B;
Port[$3D6] := Port[$3D6] and $FD;
Selecting a bank can be done with the following procedure:
Port[$3D6] := $0B;
Port[$3D7] := bank_number;
where bank_number = 0 - 3. Each bank is 64K long and has a 86K granularity.
The 452 and 453 banks have a 16K granularity, so if you want 64K granularity
you must multiply the bank number by 4 before writing it to the registers :
Port[$3D6] := $10;
Port[$3D7] := bank_number Shl 2; { = bank_numer * 4 }
The 452 and 453 allow duel paging. The 64K host address space is split in
two, one low area A000:0000-7FFFh and a high area A000:8000-FFFFh. This
mode can be enabled with the following procedure:
Port[$3D6] := $10;
Port[$3D6] := Port[$3D6] or 2;
In this mode each bank also has a granularity of 16K. The lower bank is
selected with the same procedure for setting the bank in single-paging
mode. The upper bank is selected with the following call:
Port[$3D6] := $11;
Port[$3D7] := bank_number Shl 2; { = bank_numer * 4 }
None of the CAT chips allow you to select one bank for reading and
another for writing.
┌──────────────────────────────────────────┬─────────────────────────────────
│ CAT Get Controller Information BIOS Call │
└──────────────────────────────────────────┘
Int 10h
Inputs :
AH = 5Fh Extended VGA Control
AL = 00h Get Controller Information
Returns:
AL = 5Fh Extended VGA control function supported
BL = Chip type bits 7-4 contain the chip type number
0 = 82c451
1 = 82c452
2 = 82c455
? = 82c453
bits 3-0 contain the revision number
BH = Memory Size Video memory size
0 = 256k
1 = 512k
2 = 1M