Epson EQUITY 386SX/16 PLUS - Manual (Page 212)

Before running the test, be sure that the printer is on-line,
paper is loaded, and all connections are secure, or you may
see one of the following error messages:
Error - Printer out of paper
Error - Printer not selected
Error - Printer interface
I/O
error
Error - Time out on printer
Communication Adapter Test
Before running this test on your serial port, you must
connect a special RS-232C, AT-type loopback connector to
the port, This connector enables the test to send out data and
receive the same data back on one line. You can purchase the
connector from most electronic supply stores.
Be sure the connector is configured with the following
settings:
RD and TD shorted
DSR and DTR shorted
CTS and RTS shorted.
This test resets the computer to check for possible errors.
Then it checks the port by sending and receiving data and
testing the following port parameters:
9600 baud rate
Odd parity
2 stop bits
8-bit data length.
C-24 Performing System Diagnostics