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Typewriter. The terminal may be used for normal
office typing without entering or affecting the buffer
(Enter key not operated prior to typing). If the
terminal is polled or addressed while operating in
local mode, a (
) negative-response signal is sent
n
to the CPU.
The Attention light and audible alarm
also turn on when the terminal is addressed.
Communicate
When operating in communicate mode, the terminal
will be in one of five status conditions:
Standby. Terminal is in a ready condition and capable
of sending or receiving data; however, the keyboard
is locked until an operation is initiated (see Com
municate Mode under Principles of Operation,
Model 2 for other conditions that lock the keyboard).
If the terminal is addressed while in standby status,
it responds with a @ positive response and shifts to
receive status.
Transm it. Terminal is in the process of sending
data to the communications line from the buffer.
Enter.
Terminal prints and loads the operator-
initiated information from the keyboard into the
buffer. If the terminal is addressed while in enter
status, the Attention light turns on, the alarm
sounds, and a (N) negative-response signal is sent
to the CPU. If the terminal is polled while in enter
status, it responds with a (
signal to the CPU.
Receive. Terminal is receiving data from the com
munications line or printing the received data. If
the Buffered Receive feature is installed and the
terminal is addressed while printing from the buffer,
the Attention light turns on, the alarm sounds, and a
(
) negative response is sent to the CPU. If the
n
terminal is polled while printing from the buffer, the
terminal responds with a (N) negative-response sig
nal to the CPU.
Bid. Operator has pressed the Bid key and terminal
is waiting to be polled in order to transmit the data
residing in the buffer. If the terminal is addressed
while in bid status, it responds with a (
response signal, and turns on the Attention light
and audible alarm.
Codes, Keyboard Arrangements, and Print Elements
Since the 2740 Model 2 is designed to operate pri
marily with an IBM System/360 on a multipoint
basis, the use of the PTTC/EBCD code (with its
) negative-response
n
) negative-
n
associated keyboard arrangement and print element
containing System/360 graphics), is recommended
(see Code Charts and Keyboard Arrangements in
Appendix). The PTTC/BCD code and the C orres
pondence code, with their associated print elements
and keyboard arrangements, can be requested on an
RPQ (Request Price Quotation) basis.
NOTE: The PTTC/BCD code and Correspondence code are not
System /360 Type 1 program supported.
The backspace code cannot be transmitted by the
Model 2 terminal and is used only for e rro r-
correction purposes prior to transmitting the mes
sage. However, backspace codes received by the
Model 2 terminal from the CPU will cause normal
backspacing to occur.
Transmission Controls and Indicators, Model 2
The reader should be fam iliar with the operation of
the IBM 2740 Communication Terminal as described
in the 2740 Model 1 section of this manual, and the
IBM 2740/2741 Communication Terminal—Operator's
Guide, Form A27-3001.
lights, and switches, or those keys, lights, and
switches whose functions are altered in the Model
2, are described in this section of the manual.
The (
) EOB key and (c) EOT key have been r e
b
moved from the IBM 2740 Model 2 keyboard, since
those signals are provided automatically; however,
the (B) EOB signal is provided only if the Record
Checking special feature is installed.
On/Off Power Switch
This switch (see Figure 20) controls all terminal
power. Each time power is turned on, all electronic
controls are reset.
The buffer is reset when power
is turned off.
When the terminal is attached to an active com
munications line, power should be left turned on.
Turning power on and off places power transients on
the communications line with a possibility of dis
rupting line operation.
The typewriter motor runs
only when the terminal is active and turns off auto
matically when the terminal is not being used.
Keys
The following keys are located to the left and to the
right of the 2740 Model 2 keyboard, Figures 19 and
.
2 0
Enter Key. The Enter key, when operated, enables
keyboard-initiated data to enter the buffer in either
IBM 2740 Communication Terminal, Model 2
Only the additional keys,
29
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