Epson Equity Ie Q50188015-1 - Manual (Page 104)

Insert the loop-back connector. Then press Y and Enter to start the check.
The computer checks the port by writing and reading data and control
information, and reports errors for any pins that are faulty.
Serial Port (RS-232C Port) Check
Use this option to test the functions of the primary serial communications
(RS-232C) port.
To perform the test, you must insert a special loop-back connector into the
serial port so that the computer can check the individual pins of the port.
Contact your dealer if you need a loop-back connector. Note that a different
loop-back connector is required to test the parallel port.
When you select option 11 from the DEVICE LIST menu, you see this
message:
Attach loop-back connector to serial port.
Enter Y to start this check when connector is
attached, or
Enter N to return to the menu.
Insert the loop-back connector. Then press Y and Enter to start the check.
First, the computer checks the serial port control lines to see that they are
able to change from high to low and vice versa. No messages are displayed
during this part of the test unless an error occurs.
The second test is an echo back check during which the port sends data to
itself in a fixed data format, at all the possible baud rates. When this test
begins, you see this message:
RS232C
echo back check - at various baud rates
Current baud rate is 75
Current test data is 00
D-16 Performing System Diagnostics