NMEA 0183

showstack / protocols / nmea-0183

Also called NMEA, GPS sentences.

The plain-text sentence format a GNSS receiver speaks. Lines of comma-separated ASCII beginning with a dollar sign carry position, fix quality, satellite count, speed and — the field that matters most on a show site — UTC time. It is the reason a GNSS antenna is usually feeding a master clock rather than a map.

Tracking and positionPaid specNational Marine Electronics…Reported

Stewarded by National Marine Electronics Association.

Control Small, urgent, must arrive

Small messages that either repeat constantly or fire once. Bandwidth is almost never the problem.

What kills it. Latency and loss on the messages that fire once. A repeating level survives a dropped packet; a GO does not.

The four flows, and why the model is worth having →

What goes wrong

The sentences carry time, but the precise timing comes from the receiver's 1PPS hardware output, not from the serial data. Reading time from the text alone gives you tens of milliseconds of uncertainty at best.

GNSS time and UTC differ by a whole number of leap seconds, and receivers report this differently. Check which one a device is giving you before trusting it.

It needs sky. Indoors, or hemmed in by structures, a receiver either gets no fix or gets one built from reflections — which is worse, because it looks like a fix.

NMEA 2000 is a completely different thing: a CAN-based binary bus, not this.

What speaks NMEA 0183 (1)

Product	Direction	Notes
Evertz 5601MSC Master Sync and Clock Evertz	in	GNSS discipline.

Typical use

A GNSS receiver disciplining a master clock or timecode generator, usually alongside a one-pulse-per-second hardware output.
Position and heading for tracking, survey and outdoor installation work.
Time of day for systems with no network path to an NTP server.

Sources

NMEA 0183 Interface Standard — National Marine Electronics Association primary

Understand the mechanism

How it all runs together How a machine reads the world

Something wrong, or missing?

Known gaps on this entry: default_ports, first_published, implementations, spec_url. If you can source one of them, that is a ten minute pull request.

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