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Standard Features
The 4979 has the following standard features:
Cycle Steal
The display station operates in cycle steal mode. In
cycle steal mode I/O operations are overlapped with
processing operations, so that processing can continue
while I/O operations are in progress.
Electronic Lock Out Feature
An electronic lock out feature protects against unauthorized
operator entry. This feature is provided under program
control. See "Interrupt Request Keys" in Chapter 2.
Data Protect Feature
The data protect feature prohibits the operator from
altering protected data. This feature is provided under
program control.
Character Set
The display station uses a 64 character subset of EBCDIC
(Extended Binary Coded Decimal Interchange Code).
Basic Components
The display station has two basic components:
• Display screen
• Console keyboard
Video Screen
The video screen displays keyboard
input.
The keyboard is used for keying information
into the system, altering data, starting and
stopping programs, and so on.
Figure 1-2. Basic Components (screen, keyboard)
1-2
GA34-o026
Display Screen
The display screen (Figure 1-2) is a 12-inch CRT (cathode
ray tube) similar to that of a television receiver. It
has a capacity of 1920 characters arranged in a format of
24 lines of 80 characters each. The display provides a
buffer for storing data, the capacity of the buffer is the
same as the character capacity of the screen.
Characters displayed consist of dots generated in a
pseudo 7 x 7 dot matrix on a raster CRT scanned screen.
All information displayed on the screen must be
regenerated periodically for retention of the image. The
speed at which the display is reproduced is called the
"refresh" rate. The 4979 is designed to "refresh" the
display approximately 60 times per second, creating an easy
to read display under normal lighting conditions.
Keyboard
The display station keyboard (Figure 1-2) is similar to
that of a data entry style key layout. The alphanumeric,
punctuation, and special character keys form the main
body of the keyboard with special control keys on each
side.
The keyboard is arranged in four different key groups:
• Shift/Lock Keys
• Graphic Alphanumeric
• Local Function
• Interrupt Request
All keys are color coded for ease of use:
• Alphabetic and graphic keys are white keys with black
letters.
• Numeric keys are light gray keys with uppershift
numbers in white and lowershift characters in black.
• Local Function and Interrupt keys are charcoal gray
keys with white letters or symbols.
The keyboard character set is:
A through Z
o
through 9
$,.+-*/%@&'#
( ) 4 \
=
> <
! " ?
-
I : ; -,
Space
o
o
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