NMEA 0183
NMEA 0183 (or NMEA for short) is a combined electrical and data specification for communication between marine electronic devices such as echo sounder, sonars, anemometer (wind speed and direction), gyrocompass, autopilot, GPS receivers and many other types of instruments. It has been defined by, and is controlled by, the U.S.-based National Marine Electronics Association.
The NMEA 0183 standard uses a simple ASCII, serial communications protocol that defines how data is transmitted in a "sentence" from one "talker" to multiple "listeners" at a time. Through the use of intermediate expanders, a talker can have a unidirectional conversation with a nearly unlimited number of listeners, and using multiplexers, multiple sensors can talk to a single computer port.
At the application layer, the standard also defines the contents of each sentence (message) type so that all listeners can parse messages accurately.
Contents |
[edit] Serial configuration (data link layer)
| Typical Bit rate | 4,800 |
| Data bits | 8 |
| Parity | None |
| Stop bits | 1 |
| Handshake | None |
AIS units use a default baud rate of 38,400.
[edit] Application layer protocol rules
- Each message's starting character is a dollar sign.
- The next five characters identify the talker (two characters) and the type of message (three characters).
- All data fields that follow are comma-delimited.
- Where data is unavailable, the corresponding field contains NUL bytes (e.g., in "123,,456", the second field's data is unavailable).
- The first character that immediately follows the last data field character is an asterisk.
- The asterisk is immediately followed by a two-digit checksum representing a hex number. The checksum is the exclusive OR of all characters between the $ and *. According to the official specification, the checksum is optional for most data sentences, but is compulsory for RMA, RMB, and RMC (among others).
- <CR><LF> ends the message.
As an example, a waypoint arrival alarm has the form:
- $GPAAM,A,A,0.10,N,WPTNME*32
where:
| GP | Talker ID (GP for a GPS unit, GL for a GLONASS) |
| AAM | Arrival alarm |
| A | Arrival circle entered |
| A | Perpendicular passed |
| 0.10 | Circle radius |
| N | Nautical miles |
| WPTNME | Waypoint name |
| *32 | Checksum data |
The new standard, NMEA 2000, accommodates several talkers at a higher baud rate, without using a central hub.
The NMEA standard is proprietary and sells for at least US$ 325 as of June 2010.[1] However, much of it has been reverse-engineered from public sources and is available in references like gpsd and Dale DePriest's.
[edit] Vendor extensions
Most GPS manufacturers include special messages in addition to the standard NMEA set in their products for maintenance and diagnostics purposes. These extended messages are not standardized at all and are normally different from vendor to vendor.
[edit] Software compatibility
- NMEA 0183 GPS compliant software
- NetStumbler
- Rand McNally StreetFinder
- Magic e-Map
- NemaTalker NMEA instrument simulation
- Microsoft Streets & Trips
- Microsoft MapPoint
- Serotonin Mango M2M[2] (suitable for NMEA compliant weather stations)
- MapKing
- gpsd - Unix GPS Daemon
- GPSy X for Mac OS X[3]
- Turbo GPS PC/PPC/Android[4]
- GRLevelX Weather Suite[5]
- Google Maps Mobile Edition [6]
- JOSM - OpenStreetMap Map Editor
- PolarCOM - a set of digital and analog NMEA instruments[7]
- Avia Sail - PC instruments for both NMEA 0183 and NMEA 2000 [8]
- VisualGPS - A free NMEA Monitoring utility for NMEA 0183 GPS devices[9]
- DeLorme Street Atlas
[edit] See also
- NMEA 2000
- ASCII
- Global Positioning System
- Serial communications
- Marine electronics
- Navigation system companies
[edit] References
- ^ Publications and Standards from the National Marine Electronics Association (NMEA) / NMEA 0183
- ^ http://mango.serotoninsoftware.com/
- ^ http://www.gpsy.com/
- ^ http://www.turboirc.com/tgps/
- ^ http://www.grlevelx.com/
- ^ http://www.google.com/mobile/default/maps.html
- ^ http://www.polarnavy.com/main/prod2
- ^ http://www.aviasail.com
- ^ http://www.visualgps.net/VisualGPS
[edit] External links
- National Marine Electronics Association
- NMEA's website about NMEA 0183
- NMEA data information
- Sirf-Chipset NMEA data reference manual
- Free C library for parsing and generation of the NMEA protocol
- Open Source (New BSD License) C# library for parsing NMEA protocol
- NMEA Specifications at APRS Info
- MTK proprietary NMEA extensions
