IBM Series 1 User Manual page 129

Selection of the Optimum Interface
This section discusses the advantages and disadvantages of
using the following interfaces for attachment of an OEM
device:
Non-isolated current loop interface
Isolated current loop interface
EIA voltage level interface
TTL voltage level interface
Most OEM devices that can be attached to the teletypewriter
adapter card are manufactured with a current loop interface
as basic, and an EIA voltage level interface as an
additional cost feature. Therefore, the cost of the OEM
device is generally less if the device is attached in
current loop mode.
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 EIA interface:
Transmit
Receive
Request to send
Clear to send
Data set ready
Data terminal ready
Carrier detect
Signal ground
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:
1} The transmit, receive, and signal ground signals
may
be
connected to the teletypewriter adapter card.
2} The data terminal ready signal from the teletypewriter
adapter card must be connected to the data set ready
and to the carrier detect signals.
3} 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.
4-6 GA34-0033
f
l
\
~