IBM 2250 3 Manual page 6

absolute or incremental mode in the form of points
or straight lines in any direction; it can also display
alphameric characters (alphabetics, numerics, and
special symbols). In addition, a light pen is provided
with the basic 2250-3. For increased intercommu-
nication between the user and the controlling program,
two keyboards are available as special features:
Alphameric Keyboard - Provides a typewriter-like
keyboard with which the user can perform editing
functions and compose messages consisting of letters,
numbers, and/ or special symbols for entry into 2840
buffer and CPU main storage.
Programmed Function Keyboard - Provides com-
munication between the user and the computer. The
keyboard consists of keys, indicators, and sensing
switches for use with replaceable descriptive over-
lays. The function of each key and indicator, which
is program-defined, is identified to the program by
the overlay coding and to the user by symbols on the
overlay. The program associated with the overlay
code and the selected key then directs the requested
operation. For example, as a result of a key de-
pression, the program might direct the computer to
enlarge, reduce, or delete the image displayed by the
associated 2250.
When a 2250 is not in the same room with the 2840
and the CPU, a telephone should be near the 2250 so
that the 2250 operator can communicate with the CPU
installation.
The basic 2840-2 contains a 32, 768-byte core
buffer, order mode control, and a character gener-
ator. The character generator can translate one
System/360 eight-bit byte representation from an
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alphameric character into a sequence of signals
which, when converted to analog deflection signals
by the 2250-3, cause the character to be drawn on
the 2250-3 CRT display area. A standard character
set of 63 alphabetics, numerics, and special symbols
is provided; two character sizes are program-
selectable. The basic 2840-2 can attach to, and con-
1
trol, two 2250-3's. A special feature, Display
Multiplexer, is available for increased 2840-2
attachment capability:
Display Multiplexer - Allows attachment of two
additional 2250 Model 3 Display Units to the 2840-2.
A maximum of one display multiplexer feature can
be installed on one 2840-2, allowing attachment of
up to four 2250-3's.
Display Copier Attachment - Permits attachment
of an IBM 2285 Display Copier to the 2250. The
publication Component Description, IBM 2285
Display Copier, Form GA27-2730, contains a
functional description of, and operator procedures
for, the 2285. The 2285 is a free-standing, non-
programmed device; it provides, under 2250
operator control, 8-1/2 by 11-inch paper copies of
the 2250 display image. Each copy consists of a
black image on a light gray background. The 2285
is located beside the left edge of the 2250 reading
board; in this position, the 2285 controls, indicators,
and hopper (copy receptacle) are easily accessible
to the 2250 operator. Basic power for the 2285 is
provided by the 2250. Analog signals are switched
from the 2250 to the 2285 during the paper-exposure
portion of each copy cycle.