NMEA 2000, often abbreviated to NMEA2K or N2K, uses Controller Area Network (CAN) technology that was originally designed for the automotive industry. NMEA 2000 is built on the SAE J1939 high-level protocol, but uses its own messaging scheme. However, NMEA 2000 devices and J1939 devices can operate on the same physical network.
NMEA 2000 is an updated version of the NMEA 0183 serial data bus standard. NMEA 2000 has significantly higher data rates than NMEA 0183 (250k bits/sec vs. 4800 bits/sec). It also uses a compact binary message format instead of the ASCII serial communication protocol. In addition, NMEA 2000 supports a standardized multi-talker, multi-listener data network. This listener data network is more advanced than the single-talk multi-listener (simplex) serial communication protocol used by NMEA 0183. As a result, NMEA 2000 provides better performance and more reliable communications for marine vessels.
Marine owners and product installers use NMEA 2000 to establish a system of connected devices on a vessel. To set up this network, compatible devices are connected to a central cable (called a backbone) via T-connectors and drop cables. The backbone acts as the central link between all devices connected to the network. It provides power to each instrument and passes digital information throughout the system.
Like the SAE J1939 network on which it is based, the NMEA 2000 network uses a bus topology that requires a 120Ω (ohm) termination resistor at each end of the bus. These resistors are connected in parallel, giving a total resistance of 60Ω for a properly terminated bus. The maximum distance any device can be from the bus is 100 meters, while the maximum backbone cable length is 328 meters.
With NMEA 2000, a display unit can show multiple sources of information simultaneously. This means that different tools can work together without conflict. Even if a single device fails or becomes unresponsive, the rest of the network can still operate and share information.
NMEA 2000 networks operate on a 12 volt DC power supply. A connector with positive and ground wires (including an inline fuse for the positive wire) provides onboard power to the network backbone. These power wires should be connected near the center of the backbone to ensure proper system operation.
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