IBM 1 Series Manual page 112

The only EIA-level signals that the teletypewriter adapter card generates
are 'transmit,' 'receive,' 'signal ground,' and 'data terminal ready.' If the
teletypewriter adapter is connected to an OEM device with the preceding
signals:
e The 'transmit,' 'receive,' and 'signal ground' signals may be connected
to the teletypewriter adapter card.
e The 'data terminal ready' signal from the teletypewriter adapter card
must be connected to the 'data set ready' and the 'carrier detect'
signals.
e The 'request to send' signal must be wired to the 'clear to send' signal
at the device end of the cable between the teletypewriter adapter and
the OEM device.
There are two different current loop interface "'ports'' available on the
teletypewriter adapter card: one for isolated loops and one for nonisolated
loops. The isolated current loop interface requires the user to supply power
to drive the two isolated current loops. A separate power supply and
current limiting resistor must be placed in the transmit loop and the
receive loop. Refer to ""Teletypewriter Device Information" in this chapter
for connection of these power supplies and resistors.
The teletypewriter adapter supplies the power to drive the transmit and
receive current loops when the nonisolated current loop interface is used.
There are two other significant differences between the isolated and
nonisolated current loop:
1. On the isolated current loop, the receive inputs are totally isolated. On
the nonisolated current loop, the receive inputs are coupled through
resistors to +12 volts and —12 volts generated by the card file power
supply. For both isolated and nonisolated current loops, transmit minus
is logical ground.
2. On the isolated current loop, the transmit output is a current sink. On
the nonisolated current loop, the transmit output is a current source.
Figures 4-2 and 4-3 show details of the different interfaces available on
the teletypewriter adapter card.
Teletypewriter Adapter Feature 4-7