2741 Break 0- Bit--Command Reject
This sense bit is set during initial selection:
1. By the interface controls if a command that is
not defined or cannot be executed by the 2703 is presented. This occurs if the Dial command
is issued and the Autocall Adapter has not been
installed in the 2703. The Dial command is
accepted but then rejected if issued to a line
not associated with an installed Autocall
Adapter.
2. By the terminal controls if an associated line
has been issued the Poll or Search command.
The Poll or Search is not executed, but is
ended immediately.
This sense bit is never set for the Read, Write,
Break, Prepare, Wrap, Enable, Disable, Inhibit,
or Sense commands.
1-Bit--Intervention Required
If a Read, Inhibit, Write, or Prepare command is
being executed and the addressed line has a data
line set attached, this bit is set:
1. If the data set has power off.
2. If the data set is "on-hook. " 3. If the data set is not in data mode.
4. If a data set is not attached to the 2703. 5. For the Read and Ir.hibit commands only, if a
continuous Space signal is received for one
character time or greater.
6. If, during transmit, a line is at Space for a
minimum of two successive characters.
7. If Dial is being executed, if the ACU's Power Indicator is OFF. 8. If the ACU is not connected to the 2703. This bit is never set under the Wrap, Enable, Dis­
able, or Sense commands.
4-Bit--Data Check
This sense bit is set:
1. During the execution of a Read or Inhibit
command if the line is at Space at stop-bit
time (2703 is out of sync).
2. When the line is executing Write or Wrap if a VRC; error is detected in one of the characters
being transmitted.
34.1

3. During Read or Inhibit when a VRC error is
detected.
This sense bit is not set during the execution of Dial,
Prepare, Enable, Disable, or Sense commands.
7 -Bit--Timeout
This sense bit is set:
1. During the execution of the Read command if
no characters are received for a continuous
period of three seconds when the line receive­
control bit is OFF. Otherwise, a 28-second
timeout applies.
2. During the execution of Dial if the ACU' s ACR
(Abandon Call and Retry) line turns ON. This
indicates that the call was not established in
the allotted time period and should be redialed.
3. During the execution of a Prepare command if
a continuous Space signal has been received for
more than 28 seconds.
4. During the execution of Disable if a switched­
network data set does not go "on-hook" within
28 seconds after being signaled to do so.
This sense bit is not set during the execution of
Write, Wrap, Break, or Sense. START/STOP SPECIAL FEATURES The features described here pertain only to start/
stop type operation. However, the maximum allow­
able features (see Figure 3) for a given configuration
is influenced by the feature mix for both start/stop
and synchronous in the areas of Line Sets, 2712
Adapter, and Synchronous Clock; the "Feature
Limitations per 2703" under "Special Features Summary" gives more detailed information.
Terminal Controls One terminal control is required, although as many
as six may be chosen (four start/stop and two
synchronous) for any 2703 Transmission Control. One terminal control may service all terminals of
the same type. The following start/stop type terminal
controls are available for use.
IBM Terminal Control Type I
A maximum of one per 2703 is permitted. This
feature allows for the attachment of:
IBM 1050 Data Communication
IBM 1060 Data Communication System IBM 1070 Process Communication System IBM 2740 Communication Terminal IBM 2741 Communication Terminal (without
Interrupt Feature)
IBM Terminal Control Type I also provides VRC
and LRC (vertical and longitudinal redundancy check
checking capabilities.
Type I Terminal Interrupt Feature
A maximum of one per 2703 is permitted. The
Type I Terminal Interrupt feature provides the
necessary control for an IBM Terminal Control
Type I to operate with an IBM 1050 or IBM 2741,
either equipped with interrupt features. The IBM
Terminal Control Type I is a prerequisite for the
Interrupt feature. The feature is program supported
by the Time Sharing Option (TSO) of the System/360 Operating System.
Line adapter features in the 2703 and communi­
cations facilities are the same as those now required
for IBM Type I lines. Either full duplex IBM modems
or full duplex data sets are required to take full
advantage of the Type I Terminal Interrupt feature.
The Type I Terminal Interrupt feature allows the
IBM Terminal Control Type I to be used with 1060, 1070, 2740, and 1050 or 2741 (without interrupt
features) terminals.
2741 Break Feature
A maximum of one per 2703 is permitted. This fea­
ture permits the IBM Terminal Control Type I to
operate with an IBM 2741 equipped with the Interrupt
feature, thus accommodating various time-sharing
applications utilizing the 2741. The IBM Terminal
Control Type I is a prerequisite.
This Break feature does not prohibit using the
IBM Terminal Control Type I for operation with 1050, 1060, 1070, 2740, and 2741 (without Interrupt
feature) terminals.
IBM Terminal Control Type II
A maximum of one per 2703 is permitted. This
feature allow s for the attachment of:
IBM 1030 Data Collection System, except for the 1032 Digital Time Unit
Telegraph Terminal Control Type I
A maximum of one per 2703 is permitted. This
feature allows for the attachment of:
AT&T 83B2/83B3 Selective Calling Stations
Western Union Plan 115A Outstations Telegraph Terminal Control Type II
A maximum of one per 2703 is permitted. This
feature allows for the attachment of:
35