277 lines
11 KiB
Plaintext
277 lines
11 KiB
Plaintext
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Character Attributes on Video Boards for the IBM PC
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1. Introduction
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This document describes the result of some testing of character attributes
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on various video adaptor boards for the IBM PC. These boards may vary in
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their handling of the attribute byte, especially when emulating the IBM
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Monochrome Display and Adaptor; thus text which is readable on one board
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may not be visible on another, or its characteristics may be different.
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Currently, only the IBM Monochrome Display and Printer Adaptor, the
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Tecmar Graphics Master and the IBM Enhanced Graphics Adaptor are described.
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Information on other boards is solicited.
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2. Terminology
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The following diagram shows the attribute byte layout (the byte which follows
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each character byte in the regen memory of the video adaptor boards). The
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bit fields "B", "bg", and "fg" will be referred to in the following discussion.
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+---+---+---+---+---+---+---+---+
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| B | bg | fg |
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+---+---+---+---+---+---+---+---+
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bit: 7 6 5 4 3 2 1 0
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(msb) (lsb)
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Abbreviations for video boards:
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CGMA = IBM Color/Graphics Monitor Adaptor
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MDPA = IBM Monochrome Display and Printer Adaptor
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EGA = IBM Enhanced Graphics Adaptor
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TGM = Tecmar Graphics Master
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3. Blink/Bright bit ("B")
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First, port 3D8 bit 5 of the IBM Color/Graphics adaptor is supposed to control
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the function of the "B" bit:
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port 3D8 bit 5 = 0 ==> B bit = 0, dim background colors
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B bit = 1, bright background colors
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port 3D8 bit 5 = 1 ==> B bit = 0, char not blinking
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B bit = 1, char blinking
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On the IBM CGMA, this works as described.
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On the MDPA, bit 5 of 3B8 disables blinking, essentially making bit "B"
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of the attribute byte a "don't care".
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(My IBM Tech Ref Manual indicates the the IBM Mono Adaptor has "CRT Control
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Port 1" at 3B8 but does not detail the function of that port).
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On the Tecmar Graphics Master (TGM) when configured to emulate the IBM CGMA,
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this works as advertised. In addition, when the TGM is configured to emulate
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the IBM Monochrome/Printer Adaptor, bit 5 of port 3B8 has an analogous effect
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(ie: makes bit "B" cause bright background).
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On the EGA this bit seems to have no effect in either mode (ie: port 3D8 in
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CGMA emulation, or port 3B8 in MDPA emulation).
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4. Attributes in CGMA mode
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Both the TGM and EGA seem to behave just as the CGMA does.
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5. Attributes in MDPA mode
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IBM Monochrome Adaptor
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bg background fg foreground
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0-6 black 0 black IF bg = 0 or 7
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7 dim IF fg = 0 0 dim otherwise
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7 black IF fg not 0 1-7 dim
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8 black IF bg = 0 or 7
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8 bright otherwise
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9-F bright
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When fg is 1 or 9, the character is underlined, with the underline being the
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same brightness as the character. The underline is scan line 12 (of 0..13).
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The underline blinks with the character (if enabled).
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The "B" bit causes the char to blink if bit 5 of port 3B8 is 1, otherwise
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has no effect.
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Tecmar Graphics Master
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bg background fg forground
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0 black 0 black
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1 dim 1 dim
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2 black 2 black
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3-7 dim 3-7 dim
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8 black
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* 0 black 9 bright
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* 1 bright A black
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* 2 black B-F bright
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* 3-7 bright
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(* = when port 3B8 bit 5 is 0, and attribute bit "B" is 1)
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When fg is 1 or 9, the character is underlined, with the underline being
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the same brightness as the char (1 = dim, 9 = bright). The underline is
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on the next to bottom scan line of the char (ie: line 12 of 0..13). The
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underline is steady, ie: does not blink when the character blinks.
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IBM Enhanced Graphics Adaptor
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bg background fg foreground
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0 black 0 black
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1-7 dim 1-7 dim
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8 black
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9-F bright
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When fg is 1 or 9, the character is underlined, ONLY if bg is 0. The
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underline is the same brightness as the char, and is on the bottom scan
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line if the char (ie: 13 of 0..13). The underline blinks when the char
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blinks.
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Bit 5 of port 3B8 does not affect the blinking versus bright.
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6. Summary of Monochrome Attribute Modes
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The following modes are the only ones supported by the IBM MDPA:
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B bg fg notes
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? 0 0 (-/-) black on black (little use)
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? 7 0 (-/D) black on dim (reverse video)
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? 0 1 (D/-) dim on black underlined
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? 0 7 (D/-) dim on black
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? 0 9 (B/-) bright on black underlined
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? 0 F (B/-) bright on black
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Note: the B bit controls blinking, unless disabled by
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port 3B8 bit 5 = 0.
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The IBM EGA can support all those and the following modes in addition:
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B bg fg notes
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? 7 F (B/D) bright on dim
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? 7 7 (D/D) dim on dim (little use)
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Note: the B bit always controls blinking.
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The Tecmar GM supports all of the above, and in addition:
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B bg fg notes
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? 7 9 (B/D) bright on dim underlined
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Note: the B bit controls blinking, if port 3B8 bit 5 = 1.
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If port 3B8 bit 5 = 0, the following modes are also supported:
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B bg fg (?/?) notes
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1 7 0 (-/B) black on bright
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1 7 1 (D/B) dim on bright underlined
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1 7 7 (D/B) dim on bright
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1 7 F (B/B) bright on bright (little use)
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7. More Information
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More information about character attributes on other IBM compatible boards
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and IBM compatible machines is needed. The program "attrib.bas" will display
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a matrix of 16 x 16 examples, one for each combination of foreground,
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background, and "B" bit values. The text displayed at each place is the
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hexadecimal value of the corresponding attribute byte. By using this program
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others can test their machines/adaptors and report back about the results.
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Try it both in "blink" and "bright" modes. See the tables at the end of
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this document and record your results there. If you will send your results
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to me I will incorporate them in future versions of this document.
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Zhahai Stewart Compuserve address 74076,252 (EMAIL)
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HiSystems
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6521 Old Stage Rd.
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Boulder, CO 80302 (303) 449-8180
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8. Reference Diagrams (see attrib.bas)
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In the following, the foreground "color" is represented by the columns 0 to F
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across the page, while the background "color" is represented by rows 0 to 7
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down the page. An additional "bottom half" is included for attributes with
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the "B" bit set, if needed.
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The entries are of the form:
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f/b, foreground intensity (over) background intensity
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where the codes are:
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B = Bright
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D = Dim
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- = Black
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Thus a dim character on a black background is D/-, while a black character
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in a bright background would be -/B. Characters with the same foreground
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and background brightness are of course unreadable and must be inferred.
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>>>>>>>>>>>> IBM MDPA <<<<<<<<<<<<<
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------------------------------ fg -----------------------------
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B bg 0 1 2 3 4 5 6 7 8 9 A B C D E F
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0 0 / D/ D/ D/ D/ D/ D/ D/ / B/ B/ B/ B/ B/ B/ B/
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0 1 D/ D/ D/ D/ D/ D/ D/ D/ B/ B/ B/ B/ B/ B/ B/ B/
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0 2 D/ D/ D/ D/ D/ D/ D/ D/ B/ B/ B/ B/ B/ B/ B/ B/
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0 3 D/ D/ D/ D/ D/ D/ D/ D/ B/ B/ B/ B/ B/ B/ B/ B/
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0 4 D/ D/ D/ D/ D/ D/ D/ D/ B/ B/ B/ B/ B/ B/ B/ B/
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0 5 D/ D/ D/ D/ D/ D/ D/ D/ B/ B/ B/ B/ B/ B/ B/ B/
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0 6 D/ D/ D/ D/ D/ D/ D/ D/ B/ B/ B/ B/ B/ B/ B/ B/
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0 7 /D D/ D/ D/ D/ D/ D/ D/ /D B/ B/ B/ B/ B/ B/ B/
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The bottom matrix with B = 1 looks the same except that the characters
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blink IF port 3B8 bit 5 is 1.
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Columns 1 and 9 are underlined. The underline blinks when the char does.
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>>>>>>>>>>> Tecmar Graphics Master <<<<<<<<<<
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------------------------------ fg -----------------------------
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B bg 0 1 2 3 4 5 6 7 8 9 A B C D E F
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0 0 -/- D/- -/- D/- D/- D/- D/- D/- -/- B/- -/- B/- B/- B/- B/- B/-
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0 1 -/D D/D -/D D/D D/D D/D D/D D/D -/D B/D -/D B/D B/D B/D B/D B/D
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0 2 -/- D/- -/- D/- D/- D/- D/- D/- -/- B/- -/- B/- B/- B/- B/- B/-
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0 3 -/D D/D -/D D/D D/D D/D D/D D/D -/D B/D -/D B/D B/D B/D B/D B/D
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0 4 -/D D/D -/D D/D D/D D/D D/D D/D -/D B/D -/D B/D B/D B/D B/D B/D
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0 5 -/D D/D -/D D/D D/D D/D D/D D/D -/D B/D -/D B/D B/D B/D B/D B/D
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0 6 -/D D/D -/D D/D D/D D/D D/D D/D -/D B/D -/D B/D B/D B/D B/D B/D
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0 7 -/D D/D -/D D/D D/D D/D D/D D/D -/D B/D -/D B/D B/D B/D B/D B/D
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If bit 5 of port 3B8 is 1, the bottom part of the matrix is the same as the
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top expect the chars are blinking. If it is 0, the dim backgrounds are
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replaced by bright ones, thus:
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1 0 -/- D/- -/- D/- D/- D/- D/- D/- -/- B/- -/- B/- B/- B/- B/- B/-
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1 1 -/B D/B -/B D/B D/B D/B D/B D/B -/B B/B -/B B/B B/B B/B B/B B/B
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1 2 -/- D/- -/- D/- D/- D/- D/- D/- -/- B/- -/- B/- B/- B/- B/- B/-
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1 3 -/B D/B -/B D/B D/B D/B D/B D/B -/B B/B -/B B/B B/B B/B B/B B/B
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1 4 -/B D/B -/B D/B D/B D/B D/B D/B -/B B/B -/B B/B B/B B/B B/B B/B
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1 5 -/B D/B -/B D/B D/B D/B D/B D/B -/B B/B -/B B/B B/B B/B B/B B/B
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1 6 -/B D/B -/B D/B D/B D/B D/B D/B -/B B/B -/B B/B B/B B/B B/B B/B
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1 7 -/B D/B -/B D/B D/B D/B D/B D/B -/B B/B -/B B/B B/B B/B B/B B/B
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Columns 1 and 9 are underlined. The underline does NOT blink.
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>>>>>>>>> IBM ENHANCED GRAPHICS ADAPTOR <<<<<<<<<<<
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------------------------------ fg -----------------------------
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B bg 0 1 2 3 4 5 6 7 8 9 A B C D E F
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0 0 -/- D/- D/- D/- D/- D/- D/- D/- -/- D/- D/- D/- D/- D/- D/- D/-
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0 1 -/D D/D D/D D/D D/D D/D D/D D/D -/D D/D D/D D/D D/D D/D D/D D/D
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0 2 -/D D/D D/D D/D D/D D/D D/D D/D -/D D/D D/D D/D D/D D/D D/D D/D
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0 3 -/D D/D D/D D/D D/D D/D D/D D/D -/D D/D D/D D/D D/D D/D D/D D/D
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0 4 -/D D/D D/D D/D D/D D/D D/D D/D -/D D/D D/D D/D D/D D/D D/D D/D
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0 5 -/D D/D D/D D/D D/D D/D D/D D/D -/D D/D D/D D/D D/D D/D D/D D/D
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0 6 -/D D/D D/D D/D D/D D/D D/D D/D -/D D/D D/D D/D D/D D/D D/D D/D
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0 7 -/D D/D D/D D/D D/D D/D D/D D/D -/D D/D D/D D/D D/D D/D D/D D/D
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The bottom half of the matric is identical except that it blinks. This
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is unaffedted by port 3B8 bit 5.
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The entries under columns 1 and 9 IN ROW 0 ONLY are underlined. The
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underline blinks when the character does.
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9. History of this document
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1/10/85 Original draft (Tecmar & EGA) by Zhahai Stewart
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1/15/85 Updated to include IBM MDPA by Zhahai Stewart
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