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dependency makes computer control of all program
procedures possible, thereby relieving the terminal
operator of these details. Each 2741 is connected to
a computer through a multiplexer by either a
privately-owried or common-carrier-provided com-
munications line. Only one 2741 is connected to a
line, thus providing direct and immediate access to
the computer.
One computer can service many IBM 2741 Com-
munication Terminals. The maximum number of
terminals depends on either the communications
facilities or the capacity and equipment of the com-
puter.
The optimum number of terminals is deter-
11lined by the specific application.
IBl\I 2740/2741 KEYBOARD PRINTER
A modified IBM Selectric I/O Keyboard Printer pro-
vides the input-output function for the 2740 and 2741
terminals.
The Selectric I/O keyboard uses mechan-
ical operation of the printer while transmitting and
electrical operation of the printer while receiving
data from the communications line.
The IBM 2741 basic keyboard is physically ident-
ical to that of the standard IBM Selectric typewriter.
Functionally, one change has been made to the key-
board.
The Selectric typewriter index key is now
labeled ATTN (attention). The indexing (line spac-
ing) function is ini tiated only by the computer.
The Selectric typewriter has the following fea-
tures:
• 10' or 12 characters-per-inch horizontal spacing.
(10 pitch is standard. )
• 15 1/2-inch paper width capacity.
•
13-inch~wide
writing line with a standard platen.
• Pin-feed platen available as a special feature.
• 6 or 8 lines-per-inch vertical spacing. (6 lines
is standard.)
Figure 3 illustrates the standard IBM Selectric type-
writer keyboard arrangement when the terminal is
used for normal correspondence and text "type {)pera-
tions. Additional keyboard arrangements and print
elements are available to provide compatibility with
the PTT /BCD (basic code for 27-10) and the PTT,'
EBeD codes. These keyboard arrangements and
codes are usually used in time sharing operations.
The PTT/BCD and PTT/EBCD keyboardarrangL-
ments are shown in Figures
-1
and 5. The choice of
keyboard must be made when the terminal is ordered.
The PTT
InCD
and PTT /EBCD print elements are
interchang-eable with each other but not with the
standard Selectric typewriter print element.
COl\IML':t\IC' ATIONS FACILITIES
The commu
r
~cations
facilities used to connect 2740' s
together and/or to a computer or to connect a 2741 to
a remote computer, can be any of the following.
In-Plant Wiring
This can be either existing or newly installed com-
munications lines. The lines may be either customer-
O\vned or common-carrier-owned (and made available
to the customer for his use). An IBM Line Adapter
or common carrier data set is used at each terminal
(Figure 6).
Out-of-Plant Wiring
These facilities are usually provided by a common-
carrier. They may be either leased private-line or
exchange (dial-up) facilities. See "Leased Private
Lines" and "Dial-Up Service" for further information.
Refer to Figure 7 .
I~RlnD~1I ~
IGJD]rnOJlIlCJITJOJLJGJ
~~~~
CLR
~GGJ~GJ~80[JG8ITl
EJURN
EOQQGJGJGJGJGJGJGJOD
ON
SET
CBJGJElGJQG][;][;]ODITlI--'-
ISH-FTI
I
OFF
I
SPACE 8AR
I
Note: When this keyboard ond associated print elements are lpecified, the Ii .. code assignments of the graphic
. characters change and are not compatible with the PTTC/BCD and PTTC/E8CD print elements and ossociated
k.ybaclrdl.
Figure 3. IBM 2741 Keyboard (Standard Selectric)
6
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