The specification also defines that the maximum number or total drop length should not exceed 78 meters. The maximum trunk length or network cable is 200 meters and the maximum drop length off the trunk is 20 meters. The 121 ohm termination resistors are added to the cable, at the two extreme ends of the trunk line.ĭevices are connected to the bus via drop cables with Tee into the network cable. Unlike CANbus the data rate does not appear to change with cable length but may be 250kbps data rate over 200 meters.
One data rate is defined at 250kbps (Bits per second) being the top end. NMEA-2000 Bus Electrical Interface Circuit Number of transitions and high resilience to external disturbance. The use of NRZ encoding ensures compact messages with a minimum The Bit Encoding used is: Non Return to Zero ( NRZ)Įncoding (with bit-stuffing) for data communication on a differential two Running over either a Shielded Twisted Pair round cable, including power and ground.Įach node uses a one of two different, five pin circular connectors, just as some implementations of CANbus. The NMEA-2000 interface is a Balanced (differential) 2-wire interface
In general only the physical layer of the OSI model is covered on this site. (CAN) specification defines the Data Link Layer. The higher-layer protocol is based on J1939 and ISO 11783. The NMEA Standards Committee developed the NMEA 2000 interface which isīased on the electrical CAN Bus.
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