NMEA 0183


NMEA 0183 is a combined electrical and data specification for communication between marine electronics such as echo sounder, sonars, anemometer, gyrocompass, autopilot, GPS receivers and many other types of instruments. It has been defined and is controlled by the National Marine Electronics Association. It replaces the earlier NMEA 0180 and NMEA 0182 standards. In leisure marine applications, it is slowly being phased out in favor of the newer NMEA 2000 standard, though NMEA 0183 remains the norm in commercial shipping.

Details

The electrical standard that is used is EIA-422, also known as RS-422, although most hardware with NMEA-0183 outputs are also able to drive a single EIA-232 port. The standard calls for optically isolated inputs. There is no requirement for isolation for the outputs.
The NMEA 0183 standard uses a simple ASCII, serial communications protocol that defines how data are 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 type, so that all listeners can parse messages accurately.
While NMEA 0183 only defines an RS-422 transport, there also exists a de facto standard in which the sentences from NMEA 0183 are placed in UDP datagrams and sent over an IP network.
The NMEA standard is proprietary and sells for at least US$2000 as of September 2020. However, much of it has been reverse-engineered from public sources.

UART settings

There is a variation of the standard called NMEA-0183HS that specifies a baud rate of 38,400. This is in general use by AIS devices.

Message structure

  • All transmitted data are printable ASCII characters between 0x20 to 0x7e
  • Data characters are all the above characters except the reserved characters
  • Reserved characters are used by NMEA0183 for the following uses:
ASCIIHexDecUse
0x0d13Carriage return
0x0a10Line feed, end delimiter
!0x2133Start of encapsulation sentence delimiter
$0x2436Start delimiter
*0x2a42Checksum delimiter
,0x2c44Field delimiter
\0x5c92TAG block delimiter
^0x5e94Code delimiter for HEX representation of ISO/IEC 8859-1 characters
~0x7e126Reserved

  • Messages have a maximum length of 82 characters, including the $ or ! starting character and the ending
  • The start character for each message can be either a $ or !
  • The next five characters identify the talker and the type of message.
  • All data fields that follow are comma-delimited.
  • Where data is unavailable, the corresponding field remains blank.
  • The first character that immediately follows the last data field character is an asterisk, but it is only included if a checksum is supplied.
  • The asterisk is immediately followed by a checksum represented as a two-digit hexadecimal number. The checksum is the bitwise exclusive OR of ASCII codes of all characters between the $ and *, not inclusive. According to the official specification, the checksum is optional for most data sentences, but is compulsory for RMA, RMB, and RMC.
  • Newline| ends the message.
As an example, a waypoint arrival alarm has the form:
Another example for AIS messages is:

NMEA sentence format

The main talker ID includes:
NMEA message mainly include the following "sentences" in the NMEA message:
SentenceDescription
$Talker ID+GGAGlobal Positioning System Fixed Data
$Talker ID+GLLGeographic Position—Latitude and Longitude
$Talker ID+GSAGNSS DOP and active satellites
$Talker ID+GSVGNSS satellites in view
$Talker ID+RMCRecommended minimum specific GPS data
$Talker ID+VTGCourse over ground and ground speed

One example, the sentence for Global Positioning System Fixed Data for GPS should be "$GPGGA".

Vendor extensions

Most GPS manufacturers include special messages in addition to the standard NMEA set in their products for maintenance and diagnostics purposes. Extended messages begin with "$P". These extended messages are not standardized.

Software compatibility

NMEA 0183 is supported by various navigation and mapping software. Notable applications include:
A sample file produced by a Tripmate 850 GPS logger. This file was produced in Leixlip, County Kildare, Ireland. The record lasts two seconds.

$GPGGA,092750.000,5321.6802,N,00630.3372,W,1,8,1.03,61.7,M,55.2,M,,*76
$GPGSA,A,3,10,07,05,02,29,04,08,13,,,,,1.72,1.03,1.38*0A
$GPGSV,3,1,11,10,63,137,17,07,61,098,15,05,59,290,20,08,54,157,30*70
$GPGSV,3,2,11,02,39,223,19,13,28,070,17,26,23,252,,04,14,186,14*79
$GPGSV,3,3,11,29,09,301,24,16,09,020,,36,,,*76
$GPRMC,092750.000,A,5321.6802,N,00630.3372,W,0.02,31.66,280511,,,A*43
$GPGGA,092751.000,5321.6802,N,00630.3371,W,1,8,1.03,61.7,M,55.3,M,,*75
$GPGSA,A,3,10,07,05,02,29,04,08,13,,,,,1.72,1.03,1.38*0A
$GPGSV,3,1,11,10,63,137,17,07,61,098,15,05,59,290,20,08,54,157,30*70
$GPGSV,3,2,11,02,39,223,16,13,28,070,17,26,23,252,,04,14,186,15*77
$GPGSV,3,3,11,29,09,301,24,16,09,020,,36,,,*76
$GPRMC,092751.000,A,5321.6802,N,00630.3371,W,0.06,31.66,280511,,,A*45

Note some blank fields, for example:
  • GSV records, which describe satellites 'visible', lack the SNR field for satellite 16 and all data for satellite 36.
  • GSA record, which lists satellites used for determining a fix and gives a DOP of the fix, contains 12 fields for satellites' numbers, but only 8 satellites were taken into account—so 4 fields remain blank.

    Revisions

NMEA 0183 continued to be maintained separately: V4.10 was published in early May 2012, and an erratum noted on 12 May 2012.
On November 27, 2018, it was issued an update to version 4.11, which supports Global Navigation Satellite Systems other than GPS. As of December 2023, NMEA has published the version 4.30 which replaces Version 4.11 and includes updates to the entire suite of GNSS sentences with significant interface updates for the use of GPS, GLONASS, GALILEO, BDS, QZSS, and NavIC/IRNSS satellite systems.
YearChangesRefs
1.??1983Initial release
2.001992Migrate from RS-232 to RS-422
2.011994
2.101995
2.201997
2.301998
3.002000
3.012002
4.002008
4.102012
4.112018
4.302023

YearChangesRefs
1.002000Initial release of 38.4K baud, known as "high speed"
1.012012