Epson Apex 20020 - Manual (Page 192)

The final test is an echo back check during which the port
sends data to itself at 9600 baud, using various data formats.
At the start of the test, you see these messages:
RS232C echo back check - with various data
formats
Current data format: 5 data bits, 1 stop bits,
parity - NONE
Current test data is 00
Once again, if any data received does not match the data sent,
a verify error occurs, and the computer reports the transmitted
and received data at the time of the error.
Alternate Serial Port Check
Use this option to test the functions of an additional serial
communications (RS-232C) port. To perform the test you must
insert a special loop-back connector into the alternate serial
port so that the computer can check the individual pins of the
port.
This test is identical to the check for the primary serial port.
For more details, see the description of the Serial port
(RS-232C) check above.
Dot-matrix Printer Check
Use this option to check:
The operation of your printer in IBM-compatibility mode
The compatibility of your printer with the extended
character set used by the computer
The ability of your printer to produce bit-image graphics
and print images of the graphics screen.