Epson Equity 286 PLUS - Manual (Page 218)

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 RS232C, 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