Rs-232 Port Data Lines Loopback Test (25-Pin, Worldwide Model Only) - DEC VT420 Service Manual

16 Troubleshooting and Testing
2.2.5 RS-232 Port Data Lines Loopback Test
(25-Pin, Worldwide Model Only)
For this test, you connect the RS-232 port transmit and receive data lines
together with a loopback connector (Figure 2–2). The terminal sends a
predefined set of characters on its transmit line and receives them on
its receive line. Then the terminal compares the output characters to the
input characters. If the characters do no match, an error message appears
on the screen.
To run the test:
Use an RS-232 loopback connector, PN 12-15336-00.
1. Set up the terminal (Sections 2.2.1 and 2.2.2).
2. Connect the loopback connector to the 25-pin RS-232 port
(Figure 2–2).
3. Type one of the following sequences:
ESC [ 4 ; 2 y
ESC [ 4 ; 2 ; 9 y
NOTE
The continuously running test ends only if an error occurs or you
turn off the terminal. The keyboard does not make a bell tone
during this test.
If the test is successful:
1. The keyboard makes a bell tone.
2. The keyboard's LED indicators turn off.
3. A message appears on the screen.
VT420 OK
If the test finds an error:
The screen displays the following message. See Table 2–3.
VT420 RS-232 Port Error -- 2
Runs the test once.
Runs the test continuously.