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2702/03 LINE ADAPTERS
IBM Line Adapter
The IBM Line Adapter is a device internal to specific
IBM 2702/03 start/stop adapters. This feature pro-
vides for the direct attachment of customer-supplied
cable facilities to the 2702/03 for in-plant operation.
The use of this feature eliminates the need for an
external data set or "modem" device. The IBM Line
Adapter is a serial-serial half-duplex device that
uses frequency-shift keying for transmission over
communications lines.
This line adapter is available in two speeds:
134.5 bps and 600 bps. The terminals connected to
the 2702/03 must be provided with a like line
adapter.
When using an IBM Terminal Control Type I or
Type II with an IBM Line Adapter on common-carrier
leased private-line telephone or privately owned
two-wire communications facilities, reference should
be made to SRL manual A24-3435 for Limited Dis-
tance Line Adapter Type II requirements.
The cable supplied with the 2702/03 is a shielded
twisted-pair cable with a maximum length of 40 feet.
Each conductor is AWG 20, 10/30 stranded wire.
The cable is terminated with two inches of tinning on
each conductor. The shield is not made available
for customer connection.
Telegraph Line Adapter
The telegraph interface provides for the attachment
of domestic telegraph lines utilizing 62.5 ma neutral
Signaling. The transmit relays are mercury-wetted
contact relays, hermetically sealed, and manufac-
tured by C. P. Clare Company.
Distortion
The 2702/03 samples bits of a character ideally with
reference to the leading transition of the start bit.
However, there are three asynchronous signals that
affect the occurrence of sample time. These signals
are:
a. The data signal itself;
b. The occurrence of Line Oscillator Changes
(LOS C) , which occur everyone-eleventh of a
normal bit period; and.
c. The frequency with which a particular line is
scanned to detect the oscillator change and the
Space signal.
The 2702/03 may sample a received bit during the
sample time in the middle of the bit. Considering
this range of possible strobe times, the bit must not
be shifted or shortened by more than four-elevenths
of the bit. Thus, the acceptable received distortion
is normally 35%.
2702 Receive Circuit
The line relays in the 2702 (Figure 3-5) are protected
so that a power-off condition on the 2702 will cause a
high-wattage resistance equal to the impedance of the
receive-relay coil to be switched across the tele-
graph line. This resistance prevents overheating
the receive relay.
2703 Receive Circuit
The 2703 uses a magnetic amplifier to sense a Space
on the line in the receive direction, Figure 3-6.
Signal Parameters
Nominal Voltage: 130 volts dc, -30 + 140 volts
Nominal Current: 62,5 ma
±
2.5 ma
Logical zero or Space: current not flowing
Logical one or Mark: current flowing
Data-Set Line Adapters
Local common-carrier requirements and operating
facilities must be checked before interfaCing the
common-carrier facilities.
2702 Data-Set Line Adapter on Switched Network
Operation on a switched network with the 2702 data-
set line adapter #3233 is shown in Figure 3-7. The
following steps refer to that figure:
1.
The Enable command turns on Data-Terminal
Ready (DTR) and Request to Send (RTS).
2. Data Set Ready (DSR) and Data Carrier Detec-
tor (DCD) must be active (turned on) to end the
Enable command. The Enable command must
be ended to allow a Read or Write operation.
DCD must turn on within 28 seconds maximum
(19.4 seconds minimum) of Data Set Ready.
3. A Write command can start transmitting valid
data within a minimum of one-character-plus-
one-bit time after DCD is turned on.
If
the
communications channel and/or the receiving
device cannot handle valid data within that
time, the program must provide the proper
delay either (1) by transmitting pad characters
before the valid data (each pad character pro-
vides a one-character-time delay) or (2) by a
delay in issuing the Write command.
Communications Interfaces
3-5
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