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 by, and is controlled by, the National Marine Electronics Association.
It replaces the earlier NMEA 0180 and NMEA 0182 standards.
In marine applications, it is slowly being phased out in favor of the newer NMEA 2000
standard.
The electrical standard that is used is EIA-422, although most hardware with NMEA-0183 outputs
are also able to drive a single EIA-232 port.
Although the standard calls for isolated inputs and outputs, there are various series of hardware
that do not adhere to this requirement.
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.
Serial configuration 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.
Application layer protocol rules Each message's starting character is a dollar
sign.
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 *. According to the official specification, the checksum is optional for most data sentences,
but is compulsory for RMA, RMB, and RMC.
ends the message.
As an example, a waypoint arrival alarm has the form:
$GPAAM,A,A,0.10,N,WPTNME*32 where:
The new standard, NMEA 2000, accommodates several talkers at a higher baud rate, without
using a central hub, or round-robin packet buffering.
The NMEA standard is proprietary and sells for at least US$ 250 as of June 2013.
However, much of it has been reverse-engineered from public sources.
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 GPS compliant software
AggreGate Device Management Platform NetStumbler
Rand McNally StreetFinder Microsoft Streets & Trips
Microsoft MapPoint MapKing
gpsd - Unix GPS Daemon Google Maps Mobile Edition
JOSM - OpenStreetMap Map Editor DeLorme Street Atlas
OpenCPN - Open source navigation software Sample file
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.
C implementation of checksum generation The checksum at the end of each sentence is
the XOR of all of the bytes in the sentence, excluding the initial dollar sign.
The following C code generates a checksum for the string entered as "mystring" and prints
it to the output stream.
In
the example, a
sentence from the sample file is used.
Status NMEA 0183 continued
to be maintained separately: V4.10 was published in early May 2012, and an erratum noted on
12 May 2012.
It is not clear
whether there is any active development.
The latest NMEA announcement on the subject is older than the V4.10 standard.
See also TransducerML
IEEE 1451 IEC 61162
References
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 Free Java library for parsing of the NMEA
protocol Open Source C# library for parsing NMEA protocol
NMEA Specifications at APRS Info MTK proprietary NMEA extensions
Free C#/Java library for parsing and building NMEA sentences