Graphic displays
Introduction
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In this lecture I will be covering the
topics of |
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CRT displays |
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Text mode displays |
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Graphics displays |
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Colour map tables |
Overview
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Computers currently rely mainly on Cathode Ray Tube displays and
drive these with display cards that can operate either in character mapped or
bit mapped modes. |
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We will look at the display
characeristics and at the display card characteristics |
CRT
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Physical Characteristics |
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How it works |
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Scan control flyback and
synchronisation |
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Mono and colour displays |
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Connector details |
Physical details
Scanning
Colour display
Line and frame scan
Control inputs to monitor
Text Mode Displays
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Most basic type of computer display |
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Oriented to displaying only character
data |
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One character in buffer memory per
character on the screen. |
Text display
Use of the RAMs
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RAM A has a 80 by 25 array of bytes
corresponding to the text array. One to one mapp from these to screen
characters |
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RAM B has a 256 by 16 array of bytes
encoding the appearance of the characters |
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Both are dual ported, accessible by CPU
or display hardware |
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Contents of RAM B
Ram addresses
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RAM A |
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5 bits of vertical address from control
logic |
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7 bits of horizontal address, from
control logic |
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RAM B |
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8 bit of character code from RAM A |
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4 bit of vertical address from control
logic |
Counters
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Row counter |
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9 bits long |
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Bottom 4 bits encode row within
character |
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Top 5 bits encode which character row |
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Column counter |
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10 bits long |
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Bottom 3 bits encode column within
character |
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Top 7 bits encode character column
within row. |
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Advantages
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Uses little memory – no longer
important |
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Easy to program for text I/O |
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Fast to update |
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Disadvantages |
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Can not handle variable width fonts |
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Can not readily handle graphics |
Graphics display (VGA)
Colour map display
controller
Colour Plane display
controller
Adjacent colour displays
controller
Summary
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Images depend on raster scan displays |
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Display controllers use 2d array of
elements to generate image |
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These are either pixels or character
cells |
Where to Get More
Information
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Other training sessions |
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List books, articles, electronic
sources |
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Consulting services, other sources |