====== DeviceNet Duplicate MAC ID Protocol Summary ======
In the following explanation **Dup MAC Request/Response** means a Duplicate
MAC ID  Request/Response message at the same MAC ID as the node being described.

===== Power-up =====
  * Transmit Dup MAC request message
  * Wait 1 second (listening for replies - see 1 below)
  * Transmit Dup MAC request message
  * Wait 1 second (listening for replies - see !1 below)
  * Transition to Online State

!1 - During two 1-second timeout periods above

1a) If a Dup MAC request or response is received transition to the  Communication Fault state

!2 - While in the Online state

2a) If a Dup MAC Request message is received, send Dup MAC Response

2b) If a Dup MAC Response message is received, transition to the  Communication  Fault state. (this situation seems unlikely, but can occur if two network segments are powered up and then connected together)


There are two ways to leave the Communication Fault state:
  * manual Intervention (power cycle, device reset or other manual intervention)
  * MAC ID is changed (possibly to the same value) via the offline connection set which causes the device to re-start the media access state machine. This option is only available if the device supports the offline connection set.

Generally speaking, if a duplicate MAC ID fault occurs, you must identify the node(s) with the incorrect MAC ID, make corrections, and cycle power on the network, or remove & reconnect specific devices, to bring the network up.

If the affected devices support the offline connection set it is possible to change the MAC ID's and reset faulted devices from a configuration tool without cycling network power or disconnecting devices.


This email is intended to be a general explanation, for complete, 100% accurate information please refer to Volume I, Chapter 4-7.3 and Chapter 6 in the DeviceNet specification.

Nick Jones, Oct 15. 2002
[[http://odva.or.kr/devicenet_resources/DrDeviceNet/pc.htm | Dr. Devicenet]]