How to perform a loopback test

To perform a loopback test you will net a loopback device. For information on how to make a loopback device, please refer to [LINK:serial_communication].

You should run the test while the entire shop floor is active, (i.e. do not perform this test on Sundays), since the most frequent cause of transmission errors is electrical noise coming from either the connected CNC or other CNC's close to the serial cable.

1. Attach loopback device

Disconnect the CNC, and attach the loopback device to the connector that was previously plugged in to the CNC.

2. Stop port

Stop the port from the DNC-Max Client.

3. Open server configuration

Go to the Serial Test tab in the server configuration.

4. Select the port

Select the correct serial COM port from the serial port list.

5. Start test

Press Start Test to run the loopback test.

6. Await result

The test normally takes a couple of minutes to complete, unless a serious problem is detected.

When the test is completed, a message box summarizing the result is shown.

If the Rx/Tx field indicates Failed, make sure that the loopback device is attached. If it is, your cable or loopback device is defective or wired incorrectly.

If the RTS/CTS field indicates Failed, hardware handshaking is not working correctly. If you do not use hardware handshaking, this is not a problem.

If the DTR/DSR field indicates Failed, make sure that these signals are not required by the CNC.

It is normal for some of the higher baud rates to indicate Failed, especially if you have very long serial cables.

The maximum baud rate that did not result in any transmission errors is shown in the Max baud rate field. You should not use a baud rate higher than this.

If you experience problems at 9600 or lower baud rates, you should investigate further.

1. Check your cable

Check that the cable is properly shielded, and try to shorten or re-route the cable if possible. Keep the cables as far away from noisy machines as possible.

2. Replace cable

Try replacing the cable.

3. Serial booster

Try using a serial booster. A serial booster is a piece of hardware that amplifies the signal on the serial line.

This is useful if you have very long cables.

4. Optical or LAN transmissions cables

If your need very long transmission cables, it is sometimes necessary to replace the regular serial cables with either Optical or LAN based serial ports.

For further information, you should contact your Software dealer.