The electronics devices communicate by using a protocol defined by NMEA. NMEA has two standards available :
- NMEA 0183
- NMEA 2000
- Lightweight Ethernet (LWE)
NMEA 0183 is based on a serial communication network. NMEA 2000 is a Controller-area network based technology. In recent years, the International Electrotechnical Commission (IEC) has created a new standards suite for "Digital interfaces for navigational equipment within a ship". This is known as IEC 61162 and included NMEA 0183, NMEA 2000 and LWE.
NMEA 2000 is a protocol used to create a network of electronic devices — chiefly marine instruments—on a boat. Various instruments that meet the NMEA 2000 standard are connected to one central cable, known as a backbone. The backbone powers each instrument and relays data among all of the instruments on the network. This allows one display unit to show many different types of information. It also allows the instruments to work together, since they share data. NMEA 2000 is meant to be "plug and play" to allow devices made by different manufacturers to talk and listen to each other.
Examples of marine electronic devices to include in a network are GPS receivers, auto pilots, wind instruments, depth sounders, navigation instruments, engine instruments, andnautical chart plotters. The interconnectivity among instruments in the network allows, for example, the GPS receiver to correct the course that the autopilot is steering.
The NMEA 2000 standard was defined by, and is controlled by, the US-based National Marine Electronics Association (NMEA). Although the NMEA divulges some information regarding the standard, it claims copyright over the standard and the contents thereof are thus not publicly available. For example, the NMEA publicizes which messages exist and which fields they contain but they do not disclose how to interpret the values contained in those fields. However, enthusiasts are slowly making progress in discovering these PGN definitions.
NMEA 2000 connects devices using Controller Area Network (CAN) technology originally developed for the auto industry. 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 (IEC 61162-3) can be considered a successor to the NMEA 0183 (IEC 61162-1) serial data bus standard. It has a significantly higher data rate (250k bits/second vs. 4800 bits/second for NMEA 0183). It uses a compact binary message format as opposed to the ASCII serial communications protocol used by NMEA 0183. Another improvement is that NMEA 2000 supports a disciplined multiple-talker, multiple-listener data network whereas NMEA 0183 requires a single-talker, multiple-listener (simplex) serial communications protocol.