What is NMEA?
NMEA stands for National Marine Electronics Asscoiation which has devised numerous data telegrams to allow vessel electonic equipment to communicate with each other. The NMEA 0183 Interface Standard defines electrical signal requirements, data transmission protocol and time, and specific sentence formats for a 4800-baud serial data bus. Each bus may have only one talker but many listeners. This standard is intended to support one-way serial data transmission from a single talker to one or more listeners. This data is in printable ASCII form and may include information such as position, speed, and depth.
Typical NMEA telegrams for positioning include GGA, GLL, GST, VTG and ZDA.
More information is available from the NMEA website.