Epson 8900 Series - Manual (Page 213)

RS-422 Communication Interface
The RS-422 serial communication interface handles data structures
of the same format as those for the serial communication interface.
However, the RS-422 interface can transfer data over distances of up
to 4000 feet (1219 meters) with minimal noise interference.
Current Loop Communication Interface
The current loop (TTY) interface uses a four-wire, passive, neutral
current loop which does not interfere with the standard serial interface.
The printer can receive data via either interface, provided the other
interface is in a spacing condition or its cable is disconnected.
WARNING: Interface cables installed as part of the building
wiring must conform to the requirements of the U.S. National
Electrical Code. Contact your local inspector to determine that
the correct materials have been chosen for your installation.
Communication Interfaces 10-22