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

Common-Carrier TWX Stations (Model 33/35
Teletypewriter terminals) using 8-level code.
World Trade Telegraph Terminal Control A maximum of one per 2703 is permitted. This
feature allows for the attae hment of: World Trade teleprinters.
IBM Terminal Control Base
A maximum of one per 2703 is permitted. An IBM
Terminal Control Base must be specified for the 2703 if the user wishes to include either IBM
Terminal Control Type I, or IBM Terminal Control Type II, or both.
Telegraph Terminal Control Base
A maximum of one per 2703 is permitted. A Tele­
graph Terminal Control Base must be specified for
the 2703 if the user wishes to include Telegraph
Terminal Control Type I, Telegraph Terminal Con­ trol Type IT, or World Trade Telegraph Terminal Control. Line Bases
A Start/Stop Line Base Type I accommodates up to
88 half-duplex lines operating at speeds up to 180 bps;
a Start/Stop Line Base Type II accommodates up to
24 half-duplex lines at speeds up to 600 bps.
A maximum of three line bases may be attached
to any 2703. However, a limitation of 176 lines per 2703 means that if three Type I bases are installed,
only 176 lines can be attached for the three bases.
The possible combinations available are shown in
Figure 8.
Base Expansion Feature
This feature is required if more than one Start/ Stop Base Type I or II is to be installed in the 2703. It is also required whenever a Syr:chronous Attach­
ment is specified. A maximum of one Base Expan­
sion feature per 2703 is permitted.
Line Sets Seven types of start/stop line sets are available.
Also, nine speed options are available tor start/
stop. The choice of line set is generally independent
of the' type of terminal but dependent on the communi­
cations facilitr specified. All lines in a given line __ __ \'- I!-" t, facilities. Table I summarizes the line sets per line
base and per 2703. The line sets av'ailable are as
follows.
Data Line Set A maximum of twelve per 2703 is permitted. This
feature provides the line terminations for connecting
to eight common-carrier-supplied data sets per
feature. The following data sets (or equivalent) can
be attached via this line set:
IBM 2711 Line Adapter Unit Western Electric 103A1 and 103A2 Western Electric 103F2 Western Electric 202D1 and 202D2 Western Union 1183A
Data Line Set Expander
This feature provides for eight additional half-
duplex line terminations as an expansion of the Data
Line Set feature. Each expander is associated with
the basic Data Line Set feature on a one-to-one basis,
up to a maximum <:f 10 per 2703. IBM Line Set 1A
This feature provides the line terminations for a
attachment to eight half-duplex privately owned lines
via IBM Limited-Distance Line Adapter Type IA
(two-wire IBM modem for distances up to 4.75
miles). It accommodates IBM 2740/2741 Communi­ cation Terminals. Maximum total of this feature and
mM Line Set 1B features cannot exceed twelve. This
feature cannot be installed if any IBM Line Set 2 is
installed.
mM Line Set 1B
This feature provides the line terminations for
attachment to eight half-duplex privately owned lines
via IBM Limited-Distance Line Adapter Type m
(four-wire mM modem for distances up to 4. 75
miles). It accommodates mM 2740/2741 Communi­ cation Terminals. Maximum total of this feature and IBl'vl Line Set lA features cannot exceed twelve. This feature cannot be installed if any IBM Line Set 2 is installed.
mM Line Set 2
This feature provides the line terminations for
attachment to eight IBAI Limited-Distance Line Tq)(' II (D.H)-\\'i re IBl\I mode 111 tor riistances 'In tu ,-" nllll',",). It alT\)[lllIlULialL.c. lL •. \l -,U. 1')".', j!Ii.(I 1 Ij'i() , alld 2';""::0 1:":7-11 Systt'lliS and termin::tb, I