Epson Apex-80 - Manual (Page 136)

Serial Interface Settings
If you are using an optional serial interface, you may need to change
the communications protocol of the printer or the computer for them
to communicate properly. The protocol used by the printer is decided
by one or two groups of DIP switches located on the serial interface
board; the protocol used by the computer can probably be altered by a
software command. It is essential that the printer and computer use
compatible protocols.
If you can, change the settings on the computer rather than the
interface board because the interface is set up at the factory to give
optimum performance in a wide range of conditions. If your dealer has
installed the interface for you, he or she should also be able to adjust
the computer and interface to achieve a good match.
If you do need to change the settings on the interface yourself,
(perhaps in order to use a different computer), refer to the manual
supplied with the interface.
E-8 Choosing and Setting Up Optional Interfaces