Information on Controller Area Network (CAN), CANopen, DeviceNet, J1939

J1939 References...

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What is NMEA 2000?
NMEA 2000 is a marine networking protocol (based on SAE J1939) defined by the NMEA (National Marine Electronics Association) and administered by them. The standard defines a means of connecting devices to a common data bus so that these devices can exchange information. The structure of the network as it will be seen in recreational boats is that there is a single backbone cable running the length of the boat, with drop cables going from the backbone to individual devices. The drop cables connect to the backbone by means of T-connectors. The network carries both data and power. A special T-connector provides 12V power to the network, and most smaller devices can be powered by the network itself and do not need their own power cables. The standard covers both the physical structure of the network (topology, cable specifications, connector specifications etc) and the higher-level protocols that allow messages to be exchanged.

NMEA 2000 Bus Description
The NMEA Standards Committee developed the NMEA 2000 interface which is based on the CAN Bus protocol as data link layer, and transceivers according to ISO 11898-2 as physical layer. The higher-layer protocol is based on J1939 and ISO 11783. The Controller Area Network (CAN) specification defines the Data Link Layer, ISO 11898 defines the Physical Layer. The CAN bus [CANbus] is a Balanced (differential) 2-wire interface running over either a Shielded Twisted Pair (STP), Un-shielded Twisted Pair (UTP), or Ribbon cable. Each node uses a Male 9-pin D connector. The Bit Encoding used is: Non Return to Zero (NRZ) encoding (with bit-stuffing) for data communication on a differential two wire bus. The use of NRZ encoding ensures compact messages with a minimum number of transitions and high resilience to external disturbance.

NMEA 2000
NMEA 2000 is a combined electrical and data specification for a marine data network for communication between marine electronic devices such as depth finders, chartplotters, navigation instruments, engines, tank level sensors, and GPS receivers. It has been defined by, and is controlled by, the US based National Marine Electronics Association (NMEA). NMEA 2000® connects devices using CAN (Controller Area Network) technology. NMEA 2000 is based on the SAE J1939 high-level protocol, but defines its own messages. NMEA 2000 devices and J1939 devices can be made to co-exist on the same physical network. NMEA 2000 can be considered a successor to the NMEA 0183 standard. It has a significantly higher data rate (250k bits/second vs. 4.8k bits/second for NMEA 0183). It also uses a compact binary message format as opposed to the ASCII serial communications protocol used by NMEA 0183. Another distinction between the two protocols is that NMEA 2000 is a multiple-talker, multiple-listener data network whereas NMEA 0183 is a single-talker, multiple-listener serial communications protocol.

The NMEA 2000 J1939-based communication for navigation systems in marine applications
The National Marine Electronics Association (NMEA) is developing a data communication standard for ship-board electronic devices. The NMEA Standards Committee Working Group 2000 has decided to use the CAN protocol as data link layer, and high-speed transceivers according to ISO 11898-2 as physical layer. The chosen higher-layer protocol is based on J1939 and ISO 11783. Some marine-specific additions will be defined within the NMEA 2000 communication and application profile specification.
The use of the 29-bit identifier is the very same as specified in J1939-21 and ISO 117873-3: the first three bits of the identifier are used to assign priority to a message, the other ID-fields are used to transmit the parameter group number (PGN) describing the content of the message, the destination and the source address. Messages may be assigned to a specific node or broadcasted to all nodes. The specification supports up to 254 virtual nodes in one CAN network.

ConnectFest set for IBEX and METS
The NMEA 2000 Network, the international standard for communication on vessels, will be demonstrated at a special event called ConnectFest, scheduled to be held at November’s International BoatBuilders' Exhibition & Conference, the National Marine Electronics Association reported in a release yesterday. IBEX will be held Nov. 1-3, at the Miami Beach Convention Center with ConnectFest taking place Nov. 2. Another ConnectFest demonstration will be held at the METS trade fair in Amsterdam on Nov. 16. The NMEA 2000 Network was developed by the National Marine Electronics Association, by a number of companies inside and outside the boating industry and with the aid of the U.S. Coast Guard Research and Development Center. It provides benefits to boat builders and the trade, including increased profitability and flexibility of installations, NMEA said. For the boating consumer, the NMEA 2000 opens up a new world of marine electronics with a system that offers the possibility of “plug and play” when their onboard product requirements change as well as certified products from a growing list of manufacturers.

NMEA 2000®: The New Backbone of Onboard Data Networking
If you appreciate the development of more options, power and reliability in today’s marine electronics, then you will love what NMEA 2000®—the new standard for onboard data networking—can do for your boat and your boating experience. And you will want to buy NMEA 2000®-certified products already on the market (and many more will be introduced soon). What is NMEA 2000®? NMEA 2000® is the industry’s new electronic communication and control protocol that allows any certified product to link to a bus (one main line) and communicate with one another. It offers "plug it in and play it" reliability for certified products. With its open architecture NMEA 2000® offers networking that simply has not been possible. With NMEA 2000®, engines, navigation, communication, sensors, alarms, monitors and much can be networked and controlled on a single system.