Appendix A – Address Claiming
Address claiming, detailed in ‘SAE J1939-81 Network Management’, is the technique used by AB devices to acquire a node address on
the CAN network. It is generally compatible with devices using fixed node addresses, as the fixed node address range is 127 (0x7F)
and below, with the dynamic address range 128 (0x80) and above. AB devices start claiming addresses at 128 (0x80), so as long as
integrator devices use node addresses less than 128 (0x80), or use address claiming, there are no node addressing conflicts.
The negotiation normally takes place within 2-3 seconds of system power up, but if ‘hot pluggable’ devices are added to the bus
later, it can occur again at that time. The J1939 spec defines a priority scheme that includes the possibility of a device successfully
claiming an address, and then later losing it to a higher priority device.
To address this and relieve the integrator of concerns about the specific mechanics of address claiming, AB devices issue a type 0xFF
‘Address Announcement’ message upon successful address claim. If they lose their address later and must claim another, they again
issue the Address Announcement. The interested integrator node(s) should listen for this message and use its source node address to
update their node address for the AB device.
In the case of multiple AB devices on a CAN bus, it is up to the integrator to use the PIN field of the address announcement to differ-
entiate among them. One suggested way to do this is to have the integrator device ‘remember’ the identity of a specific AB device,
and use that to select the address announcement to use for the node address of the device of interest.
If the integrator for some reason cannot or does not want to process CAN messages early enough to see the address announcement
at power up, they can issue the following J1939 broadcast message:
18EAFFFE [3] 00 EE 00
All devices which have claimed addresses will broadcast a J1939 message with their address information (these can be ignored). AB
devices will also broadcast a message type 0xFF address announcement, which the integrator can then process as required.
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