### Performing a Loop Back Test with DPA

Use this procedure to perform a loop back test with Digi Port Authority (DPA) .

#### Requirements

This procedure requires the installation of a loop back plug on the serial port to be tested. Loop back plugs are included with most AccelePort products, or may be obtained from your Digi supplier (Digi part number 60000401 for RJ-45, or 60000442 for DB-25). Alternatively, you can wire your own plug by following the Loop Back Plug Specifications, at the end of this page.

#### Procedure

1. Close any processes that access the port to be tested (for example, getty).
2. Install the loop back plug on the port connector.
3. Run DPA by entering `dpa` at the command prompt.
4. Use the up/down cursor movement keys to select the adapter you wish to test, and press the space bar.
5. If your adapter is a C/X, EPC/X or Xem host adapter, use the right/left cursor movement keys to select the concentrator or module to be tested, and press the space bar. If your adapter is not a C/X, EPC/X or Xem host adapter, skip this step.
6. Use the cursor movement keys to select the port to test. The up/down keys cycle through the ports, and the right/left keys cycle through concentrators or modules, so all ports associated with an adapter may be accessed from the same screen.
7. Press the T key to begin the test. The test consists of five phases, listed below with sample output.

Phase 1 Verify that the channel is not currently in use. All signals must be low. If the port is busy, a message similar to the following will appear:

            **** Port is Busy :DTR:CD:DSR:RTS
              Probable cause of failure:
            - Port is open by some process (e.g. getty).
            - Incorrect loop back connector or cable.

Phase 2 128 bytes of test data (the letter A is used) are put into the transmit buffer. If the write operation fails, a message similar to the following will appear:

            **** Loop Back Test Failure #1

After the write operation is complete, the FEP/OS (the software that runs on the adapter) is notified that data is available for transmission. At this time, the 128 bytes of data is transmitted. If the transmission fails, the following message will appear:

            **** Loop Back Test Failure #2
              Probable cause of failure:
            - Hardware failure.
            - FEP/OS or driver failure.

Phase 3 At this point, the FEP/OS should have received 128 bytes of data. If not, the following message will appear:

            **** Loop Back Test Failure #3
            **** Data Not Transferred to RX.
              Probable cause of failure:
            - Hardware failure.
            - Loop back connector not installed, or incorrectly wired.
            - FEP/OS or driver failure.

Phase 4 128 bytes of data are read from the receive buffer. If the read operation fails, the following message will appear:

            **** Loop Back Test Failure #4
              Probable cause of failure:
            - Hardware failure.
            - FEP/OS or driver failure.

Phase 5 The data that was transmitted is compared with the data that has been read from the receive buffer. If the comparison fails, the following message will appear:

            **** Loop Back Test Failure #5
              Probable cause of failure:
            - Hardware failure.
            - FEP/OS or driver failure.

If all test phases pass, the following message appears: Loop Back Test Passed. After test completion, the input and output data can be viewed. Press the I key to see the last 128 bytes of data that were put into the receive (input) buffer. Press the O key to see the last 128 bytes of data that were put into the transmit (output) buffer. The display shows the hexadecimal value of each character above the character itself. If the character is a non printing character, "|" is displayed in its place. NOTE: For security reasons, the receive buffer contents will only be displayed if the loop back test passes. Press the Q key to return to the channel monitoring screen.

### Loop Back Plug Specifications

The loop back plug for RJ-45 versions consists of a single 10-pin RJ-45 plug wired as follows:

Pin 3 connected to pins 1 and 8 (RTS to RI and CTS)
Pin 5 connected to pin 6 (TxD to RxD)
Pin 9 connected to pins 2 and 10 (DTR to DSR and DCD)

For DB-25 versions, the loop back plug consists of a female DB-25 connector wired as follows:

Pin 4 connected to pins 22 and 5 (RTS to RI and CTS)
Pin 2 connected to pin 3 (TxD to RxD)
Pin 20 connected to pins 6 and 8 (DTR to DSR and DCD)