A multiplexing data bus must be stable and must be protected against unwanted radiation interference that could corrupt the data signals. The data bus or backbone used in a J1939 multiplexed chassis is a pair of twisted wires color coded yellow and green. The reason for using a twisted-wire pair is to minimize the surface area on which outside low-level radiation or electromagnetic interference (EMI) can act on the bus. The idea is to prevent the data backbone from acting like a radio antenna. Reducing EMI (electromagnetism, radar, microwave) susceptibility is critical to protecting data from transmission corruption.
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