IBM 1 Series Manual page 111

Selection of the Optimum Interface
4-6
GA34-0033
This section discusses the advantages and disadvantages of using the
following interfaces for attachment of an OEM device:
« Nonisolated current loop interface
e Isolated current loop interface
e EKIA-voltage-level interface
e TTL-voltage-level interface
Most OEM devices that can be attached to the teletypewriter adapter card
are manufactured with both a current loop interface and an
EIA-voltage-level interface as switch-selectable options that are included
in the basic price of the device.
Some devices are manufactured with (1) only the EIA interface, (2) only
the current loop interface, or (3) one interface as standard and the other
as an addedcost feature.
Current loop mode also has more noise immunity than EIA or TTL
voltage levels.
When most OEM devices are ordered with an EIA interface, they contain
the full start-stop feature subset of the EJA interface:
e Transmit
e Receive
e Request to send
e Clear to send
« Data set ready
« Data terminal ready
e Carrier detect
e Signal ground