NMEA 0183

NMEA 0183 is the National Marine Electronics Association serial data standard that lets shipborne instruments exchange data as ASCII sentences over a single-talker, multiple-listener line. Each sentence starts with a dollar sign and a five-character identifier, such as GGA for a GNSS fix or RMC for the recommended minimum data, followed by comma-separated fields and a checksum. It runs at 4800 baud for most talkers, 38400 for AIS, over an EIA-422 differential pair. One talker, for example a GNSS receiver, feeds many listeners such as the ECDIS, radar, and autopilot. Its limits, low speed and one talker per bus, are why NMEA 2000 replaced it for networked installations.