Recently, SAE has released a revised version of the J1939-15 CAN physical layer for Unshielded Twisted Pair (UTP) cable. The bit-rate is determined to be at 250 kbit/s.
THIS SPECIFICATION PUBLISHED IN 2003 AND UPDATED IN 2008 describes a CAN high-speed physical layer (ISO 11898-2) using unshielded cables with extended stub lengths. The most important change was to loosen the restriction on the number of nodes allowed from 10 to 30 (with some admonitions about reflections and EMC). Connectors are still not specified. CAN controllers supporting the CAN FD protocol may be used, but they must not transmit CAN FD frames. It is planned to develop a new specification for J1939 allowing transmission of CAN FD frames with a second bit-rate in the data-phase.
The updated SAE Recommended Practice is intended for light- and heavy-duty vehicles on- or off-road as well as appropriate stationary applications which use vehicle derived devices (e.g., generator sets). Vehicles of interest include but are not limited to: on- and off-highway trucks and their trailers; construction equipment; and agricultural equipment and implements.
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