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Many J1939 devices do not use fixed nodeIDs to identify themselves on the network. Instead, they use an address claim mechanism:·
When a device goes active on the network, it tries to claim a certain identity.
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Other devices on the network may deny this claim.
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I.e., when they have already claimed it themselves.
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The devices will then increment its wanted ID and try again.
The same device may end up with a different ID, depending on which other devices are on the network and their boot order. It is up to the applications then, to make sure the correct data is communicated between devices.