IBM 1 Series Manual page 136

TTL
The connections for TTL are as follows:
Series/1 TTY card connector Device connector
B4 TTL received data TTL transmitted data
B5 Signal Ground Signal ground
Either
A7 SSS closed=data mark or
-TTL data out
TTL received data
B7 SSS open=data mark or
+TTL data out
Wire the cable to either pin A7 or pin B7, depending on which polarity is
required by the attached device for received data.
The interface requires a shielded, 3-conductor cable.
Current Loop With User's Power Supplies
Connections for this current loop are as follows:
Series/1 TTY card connector Device connector
Al Isolated receive input+ Transmit —
A3 Isolated receive input— Transmit +
B5 Signal ground (transmit—) Receive +
A7 SSS closed=data mark Receive —
Two external power supplies are required for the current loop interface:
one for the transmit loop and one for the receive loop. Both power
supplies must generate 25-volt power and must supply a current of up to
100 mA.
The two external power supplies must be placed in series with the transmit
and receive loops with the polarities as shown here. The power supplies
should be placed at the device end of the cable.
Figure 4-8 is a diagram for the cable connections described (that is, when
the customerelects to use external power supplies, solid-state switch
teletypewriter adapter outputs, and isolated receive inputs).
Note: For this configuration, the jumper wire that ties +12 volts into the
receiver logic should not be used (refer to Figures 4-2 and 4-7).
Teletypewriter Adapter Feature 4-31