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Justification:

For a uint4, '15' is reserved for “No Data”, and '14' is reserved for 'Error'. The former indicates that the device is not generally capable of providing the data or does not intend to share the data at this time (e.g. it needs more time to collect the data). The latter means that the device is normally capable of providing the data but is prevented at this time by some failure (e.g. a faulty sensor). These values should not be used to communicate specific data.

At first glance, it may seem that the “Bus Short” and “Not Available” values mean much the same, but the distinction is important. The “Bus Short” and “Not Available” results are entirely meaningful results, and are not indications of any problem with the measuring device such as a '14' value would indicate. They are certainly not “No Data”, as a 15 value is meant to indicate.

Note that as written, this DGN cannot be used to broadcast only the Protocol and Bit Rate fields without including the termination status. It is highly likely that designers will create bridge devices that support these two simple data fields but do not have the ability to measure the bus termination.

Please see the attached document.