Loopback Port Test

This procedure can be used to verify RealPort functionality by redirecting data through a RealPort port in which the transmit and receive pins have been tied together.

IMPORTANT

• Windows NT users should ignore this loopback procedure.  In Windows, the HyperTerminal program can be used to verify port integrity.  Refer to Windows HyperTerminal documentation.
• The loopback test procedure in DG/UX differs slightly from this procedure. Refer to the DG/UX release notes for this loopback procedure.

Procedure

1. If the port is enabled for login in the operating system, disable it.
2. Connect the port's transmit and receive lines together (pins 2 and 3 of a DB-25 connector, or the middle two pins of an RJ-45 connector). A Digi loopback plug will also work. In some cases, the DCD (Data Carrier Detect) signal may need to be active for the loopback test to succeed. See DCD Checklist.
3. Enter these commands from a root prompt:
   
   cat < /dev/tty1 &
   date > /dev/tty1
   
   Note: Use the device name of the port your are testing instead of /dev/tty1.The first cat command runs in the background, and directs all input from the device to stdout (the console screen). The date command transmits date to the device.
4. Verify the results.
   
   

   Result	Meaning
   The date appears on the console screen.	Data can be sent successfully out of the port, through the loopback plug and back into the port.
   The date does not appear on the console screen.	The date was not successfully transferred to the port, through the loopback plug, back into the port and to the console screen. In this case, try the loopback test on another port.