WHAT IS NMEA?
NMEA is the acronym for America’s National Marine Electronics Association, and it has long been the global standard for networking marine instruments. It defines what data a ‘talker’ instrument generates and how it is transferred to other ‘listener’ instruments in electronic ‘sentences’. Each sentence is designated by five letters — for example GPGLL means the following numbers refer to your latitude and longitude — followed by a string of numbers.
NMEA’S widely used 0183 protocol, launched in 1983, had a baud rate of 4,800 bits — that is, it could transmit 4,800 noughts and ones each second, equivalent to around 450 characters. But as instruments have become more numerous on board and more complex, this wasn’t fast enough. Nor was the one-way street of talkers and listeners in line with modern networking requirements. What was needed was a protocol that allowed large quantities of data to flow back and forth. The answer was NMEA 2000, which is based on the principles of a CAN bus — allowing devices to speak to each other without the need of a central computer to manage it.
N2K, as it is often abbreviated, runs at 250kb, which is 50 times faster than its predecessor. An N2K network consists of a backbone cable running from one end to the other, into which instruments are plugged by means of a T-junction.
Plugs, wires and sockets are usually pre-moulded to eliminate the potential for poor connections.