Duplicate Address Detection

Two slaves with equal addresses in the network? No problem any more!

If you are commissioning or modifying an AS-Interface network that extends wide into the field and where you cannot see all slaves at a time it may happen that accidentally there are two slaves with an identical address connected.

A master is unable to detect such a duplicate address situation reliably. If, for example, repeaters are in the network a duplicate address situation where the two slaves are in different segements of the network cannot be identified. Even diganosis tools cannot cope with all possible configurations.

The principlie of the new approach to duplicate address detection that is introduced here is comparable to that applied to maritime communication, where brief periods of silence were mandatory in order to detect weak distress signals. Applied to AS-Interface it works like this: Every slave equipped with the new duplicate address detection function does not answer every master requests to it's address. It omits the answer for one request in approximately 200 and listens to other slave answers instead that may come from another slave in the network. If there is annother slave that answers the same request there obviously is a duplicate address situation. In order not to reduce the data exchange error rate this principle is applied to organisational telegrams (like "read status" or "read ID0") only that do not contribute to that error rate. In a network with up to 62 slaves it will take a maximum of 2 minutes until a duplicate address situation is detected.

Once a slave has detected a duplicate address situation it will signal this locally with it's status LEDs. Additionally it will terminate data exchange by setting it's address to 0. This ensures that no unitended output signals will interfere with the process. This also will force the master to signal a configuration error. Further the flag S2 is set in the status register of the slave.

The advantages of this new approach in duplicate address detection are:


  • It will function reliably in all possible network configurations, even those with repeaters, and even in those cases where only of the two slaves on the same address is equipped with the duplicate address detection feature.
  • It will function with all masters and does not rely on additional electronics or special network cable routing.
  • It is possible to apply this new feature in all existing networks.
  • It provides additional safety against malfunction and, therefore, is particularly interesting for all slaves that control motors, valves or similar outputs.
If you are interested to integrate this new technology in your products please contact us.