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Technical Information on the Enhanced Graphics Adapter
EXT-Info-IBMPC-1VFRR 23-Feb-85 Info-IBMPC Digest V4 #17
From: {Info-IBMPC Digest <Info-IBMPC@USC-ISIB.ARPA>}DDN
To: {Info-IBMPC: ;}DDN
Identifier: EXT-Info-IBMPC-1VFRR
Length: 5 page(s)[estimate]
Posted: 23-Feb-85 13:10-PST Received: 5-Mar-85 09:14-PST
Message:
Return-path: <INFO-IBMPC@USC-ISIB.ARPA>
Received: from USC-ISIB.ARPA by OFFICE-2.ARPA; 23 Feb 85 15:44:23 PST
Info-IBMPC Digest Saturday, 23 February 1985 Volume 4 Issue 17
This Week's Editor: Billy Brackenridge
Today's Topics:
Extended Graphics Adaptor Tech Info
How I Got my EGA Manual, a True Story
Date: 23 Feb 1985 11:57:04 PST
Subject: Extended Graphics Adaptor Tech Info
From: Billy <BRACKENRIDGE@USC-ISIB.ARPA>
Here is a bit more technical information on the extended graphics adaptor
card. It still isn't complete, but it is a start:
The adapter memory (base) is configured a 4 16K bit planes. The graphics
memory expansion adds one bank of 16K to each of the 4 bit planes. Additional
memory may be added to increase each bit plane by another 16K.
Modes of Operation
IBM Color Display
Alpha Buffer Box Max
Mode # Type Colors Format Start Size Pages Resolution
------ ---- ------ ------ ------ ---- ----- ----------
0 A/N 16 40x25 B8000 8x8 8 320x200
1 A/N 16 40x25 B8000 8x8 8 320x200
2 A/N 16 80x25 B8000 8x8 8 640x200
3 A/N 16 80x25 B8000 8x8 8 640x200
4 APA 4 40x25 B8000 8x8 1 320x200
5 APA 4 40x25 B8000 8x8 1 320x200
6 APA 2 80x25 B8000 8x8 1 640x200
D APA 16 40x25 A8000 8x8 2/4/8 320x200
E APA 16 80x25 A8000 8x8 1/2/4 640x200
Modes 0-6 emulate CGA adapter support.
Modes 0,2,5 are identical to 1,3,4 at the adapters direct drive interface.
The maximum page fields for modes D and E indicate the number of pages for
64k,128k,256k bytes of graphics memory.
IBM Monochrome Display
Alpha Buffer Box Max
Mode # Type Colors Format Start Size Pages Resolution
------ ---- ------ ------ ------ ---- ----- ----------
7 A/N 4 80x25 B0000 9x14 8 720x350
F APA 4 80x25 A0000 8x14 1/2 640x350
Mode 7 provides Mono adapter emulation support.
IBM Enhanced Color Display
Alpha Buffer Box Max
Mode # Type Colors Format Start Size Pages Resolution
------ ---- ------ ------ ------ ---- ----- ----------
0* A/N 16/64 40x25 B8000 8x14 8 320x350
1* A/N 16/64 40x25 B8000 8x14 8 320x350
2* A/N 16/64 80x25 B8000 8x14 8 640x350
3* A/N 16/64 80x25 B8000 8x14 8 640x350
10 APA 4/64 80x25 A8000 8x14 1/2 640x350
16/64
* Note that modes 0,1,2,3 are also listed under Color Display. BIOS provides
support when enhanced display is attached.
The values in "Colors" indicates 16 colors out of a palette of 64 or 4 colors
out of 16.
Basic Operations
Alphanumeric Modes
The data format for alpha modes on the EGA is the same as the data
format on the CGA and Mono adapter cards.
As an added function, bit three of the attribute byte may be
re-defined by the Character map select register to act as a switch
between character sets. This gives the programmer access to 512
characters at one time. This function is valid only when you have
128K or more of graphics memory.
When alpha mode is selected, BIOS transfers character patters from
ROM into bit plane 2. The processor stores character data into
plane 0, and the attribute into plane 1. The programmer views
planes 0 and 1 as a single buffer in alpha modes.
The CRTC generates sequential addresses, and fetches one character
code byte and one attribute byte at one time. The character code
and row scan count address bit plane 2, which contain the character
generators. The appropriate dot patterns are then sent to the
palette in the attribute chip, where the color is assigned
according to the attribute data.
Graphics Modes
320x200 Two and Four Color Graphics (Modes 4 and 5)
--------------------------------------------------- Addressing,
mapping, and data format are the same as the 320x200 pel mode of
the CGA. The display buffer is at B8000. The bit image is stored in
bit planes 0 and 1.
640x200 Two Color Graphics (Mode 6)
-----------------------------------
Addressing, mapping and data formats are the same as the 640x200
pel mode on the CGA. Buffer starts at B8000 and bit image is in
plane 0.
640x350 Monochrome Graphics (Mode F)
---------------------------
This supports the Mono display with the following attributes:
black, video, blinking, intensified. Maps 0,1 and 2,3 are chained
together to form 2 32k bit planes. The first map is the video bit
plane, the second is the intensity plane. Both planes reside at
A0000.
Two bits, one from each plane, define one pel on the screen. The
bit definition for the pels are given in the following table. Video
plane is C0, intensity is C2.
C2 C0 Pixel Color Valid Attributes
-- -- ----------- ----------------
0 0 Black 0
0 1 Video 3
1 0 Blinking C
1 1 Intensified F
The byte organization of the memory is sequential. The first 8 pels on
the screen are defined by the contents in A000:0H, the second 8 in
A000:1, and so on. The first pel within a byte is bit 7 in the byte, the
last is bit 0.
Mono graphics works in odd/even mode, which means that odd CPU address go
to odd planes, and even addresses to even planes. Since both planes
reside at A0000, the user must select the plane or planes to update. This
is accomplished by the map mask register of the sequencer.
16/64 Color Graphics Modes (Mode 10)
------------------------------------
These modes support graphics in 16 colors on either medium or hi
resolution monitor. This uses all four bit planes. The planes are denoted
as C0,C1,C2, and C3.
C0 = Blue Pels
C1 = Green Pels
C2 = Red Pels
C3 = Intensified Pels
Four bits (one from each plane) define one pel on the screen. Color
combinations are as follows:
I R G B Color
- - - - ------------------
0 0 0 0 Black
0 0 0 1 Blue
0 0 1 0 Green
0 0 1 1 Cyan
0 1 0 0 Red
0 1 0 1 Magenta
0 1 1 0 Brown
0 1 1 1 White
1 0 0 0 Dark Gray
1 0 0 1 Light Blue
1 0 1 0 Light Green
1 0 1 1 Light Cyan
1 1 0 0 Light Red
1 1 0 1 Light Magenta
1 1 1 0 Yellow
1 1 1 1 Intensified White
The display buffer resides at A0000, The map mask register of the
sequencer is used to select any or all of the bit planes to be updated
when a memory write to the display buffer is performed.
Color Mapping
Character Mode 10H Mode 10H
Attribute Monchrome 64KB > 64KB
--------- --------- --------- ----------
00H Black Black Black
01H Video Blue Blue
02H Black Black Green
03H Video Blue Cyan
04H Blink Red Red
05H Inten White Magenta
06H Blink Red Brown
07H Inten White White
08H Black Black Dark Grey
09H Video Blue Light Blue
0AH Black Black Light Green
0BH Video Blue Light Cyan
0CH Blink Red Light Red
0DH Inten White Light Magenta
0EH Blink Red Yellow
0FH Inten White Intens White
External Registers
------------------
This section describes registers of the EGA card not contained in the LSI
device.
Name Port Index
----------------------- ---- -----
Misc Output Register 3C2 -
Feature Control Reg 3?A -
Input Status Reg 0 3C2 -
Input Status Reg 1 3?2 -
? = B in Monchrome modes, D in color modes
Misc Output Register
--------------------
Write only. Hardware reset causes all bits to zero.
Bit 0 - 3BX/3DX CRTC I/O Address - This bit maps the CRTC I/O
addresses for the mono or CGA emulation. 0 sets the CRTC addresses to
3BX and Input status reg 1 to 3BA for mono emulation. 1 sets the CRTC
address to 3DX and status reg 1 to 3DA for CGA emulation.
Bit 1 - Enable RAM - 0 disables ram from the processor, 1 enables ram
to respond at addr's designated by the Contol Data Select value in the
Graphics Controllers.
Bit 2,3 - Clock Select, according to the following table:
Bit 2 Bit 3
----- -----
0 0 14Mhz from Processor I/O channel
0 1 16Mhz On-board clock
1 0 External clock from feature connector
1 1 Not used
Bit 4 - Disable Video Drivers - 0 activates internal video drivers, 1
disables them. When disabled, the source of the direct drive color output
becomes the feature connector.
Bit 5 - Page Bit for Odd/Even - Selects between 2 64K pages of memory
when in Odd/Even modes (0,1,2,3,7). 0 selects low pase, 1 selects high
page of memory.
Bit 6 - Horiz Retrace Polarity - 0 selects positive, 1 selects negative.
Bit 7 - Vert Retrace Polarity - 0 selects positive, 1 selects neagative.
Feature Control Register
------------------------
Write only. Ouput address is 3BA or 3DA.
Bits 0,1 - Feature Control Bits - Output of these bits go to FEAT0
(Pin19) and FEAT1 (Pin 17) of the feature connector.
Bits 2,3 - Reserved.
Bits 4-7 - Not Used.
Input Status Register Zero
--------------------------
Read Only. Input address is 3C2.
Bits 0-3 - Not Used.
Bit 4 - Switch Sense - When set to 1, this allows proc to read the 4
config switchs on the board. The setting of the CLKSEL field determines
switch to be read. The switch setting can also be determined by reading
40:88H in RAM. 0 indicates switch is closed
Bit 5,6 - Feature Code - Input from FEAT0 and FEAT1 on the feature
connector.
Bit 7 - CRT Interrupt - 1 indicates video being displayed, 0 indicates
vertical retrace is occurring.
Input Status Register One
-------------------------
Bit 0 - Display Enable - 0 indicates the CRT raster is in a Horizontal or
vertical retrace interval. This bit is real time status of display enable
signal.
Bit 1 - Light Pen Strobe - 0 indicates light pen trigger has not been
set, 1 indicates set.
Bit 2 - Light Pen Switch - 0 indicates switch closed, 1 is switch open.
Bit 3 - Vertical Retrace - 0 indicates video information being displayed,
1 indicates CRT is in vertical retrace. This bit can be programmed to
interrupt the proc at int level 2 at the start of retrace. This is done
by bits 4,5 of the Vertical End Register of the CRTC.
Bit 4,5 - Diagnostic Usage.
Bit 6,7 - Not Used.
Sequencer Registers
-------------------
Name Port Index
---------------- ---- -----
Address 3C4 -
Reset 3C5 00
Clocking Mode 3C5 01
Map Mask 3C5 02
Char Map Select 3C5 03
Memory Mode 3C5 04
Sequencer Address Register
--------------------------
A pointer register located at output address 3C4H. Loaded with a value to
indicate where the sequencer data is to be written
Bits 0-4 - Sequencer Address.
Bits 5-7 - Not Used.
Reset Register
--------------
Write only. Written to when address register is 00H.
Bit 0 - Asynchronous Reset - 0 commands the sequencer to asynchronous
clear and halt. 1 causes sequencer to run unless bit 1 is zero. Reseting
sequencer can cause loss of data in display buffer.
Bit 1 - Synchronous Reset - 0 commands sequencer to synchronous clear and
halt. bits 0 and 1 both must be 1 to allow sequencer to operate. Reset
the sequencer with this bit before changing clock mode to allow memory
contents to be preserved.
Clocking Mode Register
----------------------
Write only. Written when address register is 01H.
Bit 0 - 8/9 Dot Clocks - 0 directs sequencer to generate character clocks
9 dots wide, 1 causes 8 dots wide. Mono alpha (Mode 7) is the only mode
that uses 9 dot clocks.
Bit 1 - Bandwidth - 0 makes CRT memory cycles occur 4 out of 5 available
memory cycles; 1 makes CRT memory cycles occur on 2 out of 5 available
memory cycles. All hi-res modes must use 4 out of 5 in order to refresh
the display image.
Bit 2 - Shift Load - When 0, video serializes are reloaded every
character clock, 1 causes load every other clock. The later mode is
useful when 16 bits are fetched per cycle and chained together in the
shift registers.
Bit 3 - Dot Clock - 0 selects normal dot clocks derived from the
sequencer master input. 1 causes the clock to be divided by 2 to generate
the dot clock. Dot clock divided by to is used for modes 0,1,4,5.
Bit 4-7 - Not Used.
Map Mask Register
-----------------
Write only. Written when address register is 02H.
Bit 0-3 - Map Mask - A 1 in bits 3 through 0 enables the proc to write to
the corresponding maps 3 through 0. If this register is 0FH, the CPU can
perform a 32 bit write on a single memory cycle. Data scrolling is
enhanced when this register is 0FH. When odd/even modes are selected,
maps 0,1 and 2,3 should have the same mask value.
Character Map Select Register
-----------------------------
Write only. Written when the address register is 03H.
Bit 0,1 - Character map select B - Selects the map used to generate alpha
characters when attribute bit 3 is 0, according to the following table:
Bit1 Bit0 Map Selected Table Location
---- ---- ------------ ------------------------
0 0 0 1st 8K of Plane 2 Bank 0
0 1 1 2nd 8K of Plane 2 Bank 1
1 0 2 3rd 8K of Plane 2 Bank 2
1 1 3 4th 8K of Plane 2 Bank 3
Bit 2,3 - Character map select A - Selects the map used to generate alpha
characters when attribute bit 3 is 1, according to the following table:
Bit3 Bit2 Map Selected Table Location
---- ---- ------------ ------------------------
0 0 0 1st 8K of Plane 2 Bank 0
0 1 1 2nd 8K of Plane 2 Bank 1
1 0 2 3rd 8K of Plane 2 Bank 2
1 1 3 4th 8K of Plane 2 Bank 3
Bits 4-7 - Not used.
In alpha modes, bit 3 of the attribute byte normally has the function of
turning the forground intensity on or off. This bit may be redefined as
a switch between character sets.This function is selected only when the
values in character map select A and B are different. When they are the
same, the function is disabled. Memory mode register bit 1 must be a 1
in order to enable this function; otherwise bank 0 is always selected.
128K of memory is required for 2 character sets, 256K for 4 sets.
Memory Mode Register
--------------------
Write only. Written when address register is 04H.
Bit 0 - Alpha - 0 indicates non-alpha mode active. 1 indicates alpha mode
is active and enables character generator map select function.
Bit 1 - Extended Memory - 1 indicates memory expansion card installed. 0
indicates card not installed
Bit 2 - Odd/Even - 0 directs even processor addresses to maps 0 and 2,
odd to maps 1,3. 1 causes processor addresses to sequentially address the
bit map. The maps are accessed according to the value in the Map Mask
Register.
------------------------------
Date: Thu, 21 Feb 85 22:35:27 est
From: "John Levine, P.O.Box 349, Cambridge MA 02238-0349 (617-494-1400)"
<ima!johnl@cca-unix> Subject: How I Got my EGA Manual, a True Story
To: brackenridge@USC-ISIB.ARPA
I was in the same boat as you -- I had the Seminar Proceedings issue on
the EGA, but couldn't find the manual pages. Then out of the blue, a
local guy called me up and offered to swap a copy of the seminar
proceedings for a copy of the EGA manual. Needless to say, I took him
up on it.
It turns out that he took the totally straightforward approach, entirely
by accident, and it worked. He bought a copy of the "Options and
Adapters Technical Reference," which costs $125, a total ripoff,
particularly since almost everything in it is in the XT technical
reference, too. In the front of this manual is a postcard you send in
for the update service. Wait a month, and a mountain of updates arrives
in the mail, including the EGA manual. It is over 100 pages including a
lot of diagrams. About half of it is the assembler listing of the BIOS
code in the ROM.
John Levine, ima!johnl or Levine@YALE.ARPA
------------------------------
End of Info-IBMPC Digest
*** CREATED 03/07/85 22:56:13 BY BILL.FRANTZ/BILL ***