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Information about 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 (winds speed and direction), gyrocompass, autopilot, GPS receivers and many other types of instruments. It has been defined by, and is controlled by, the US-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 one "listener" at a time. Through the use of intermediate expanders, a talker can have a unidirectional conversation with multiple listeners, and using multiplexers, multiple sensors can talk to a single computer port. Third-party switches are available that can establish a primary and secondary talker, with automatic failover if the primary fails.

At the application layer, the standard also defines the contents of each sentence (message) type so that all listeners can parse messages accurately.

Electrical Characteristics (physical layer)

NMEA 0183 implementations vary, but can often interoperate with RS-232, RS-423, and RS-422. Each signal runs over a pair of wires. It is wise to test specific implementations for compatibility with these more widespread electrical standards, but, at the relatively slow speed of the interface, there is a high chance that it will work. Especially in a marine environment where grounding may be erratic, it can be wise to protect interfaces, especially of computer serial ports, with an optoisolator.

The official specification states that the "talker" drive circuit shall at minimum meet the requirements of EIA-422-A, a.k.a. RS-422. It also states that all "listeners" shall have optoisolators and other protective circuitry.

One frequently over-looked requirement for the "listener" portion of the circuit is the minimum level of operation. The "listener" must be able to operate with a minimum differential input voltage of 2.0 Volts and take no more than 2.0 mA current.

Serial Configuration (data link layer)

Baud Rate: 4800
Data Bits: 8
Parity: None
Stop Bits: 1 (or more)

Application Layer Protocol Rules

  • Each message starting character is a dollar sign.
  • The next first five characters identify the type of message (talker).
  • All data fields that follow are comma-delimited.
  • 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.
Example of sentence:

Waypoint Arrival Alarm

$GPAAM,A,A,0.10,N,WPTNME*32

Where: AAM Arrival Alarm A Arrival circle entered A Perpendicular passed 0.10 Circle radius N Nautical miles WPTNME Waypoint name
  • 32 Checksum data
A compound string from the NR203 GPS Receiver containing multiple messages. The actual messages decoded include…
  • ZDA – Standard NMEA $..ZDA Time & Date message
  • GLL – Standard NMEA $..GLL Geographic Position – Latitude/Longitude message
  • NSV – NMEA message containing individual satellite information.
Typical ASCII String
$<cr><lf>
MRK,0<cr><lf>
ZDA,123336.8069,17,06,2001,13.0<cr><lf>
GLL,2924.11158,N,1211.07392,W, 75.97,M<cr><lf>
VTG,218.7,T,2.38,H,0.18,V<cr><lf>
SGD,-1.0,G,-1.0,M<cr><lf>
SYS,3T,9<cr><lf>
ZEV,0.28745E-006<cr><lf>
NSV,2,00,000,00,0.0,00.0,00,00,D<cr><lf>
NSV,7,00,000,00,0.0,00.0,00,00,D<cr><lf>
NSV,28,00,000,00,0.0,00.0,00,00,N<cr><lf>
NSV,1,00,000,00,0.0,00.0,00,00,D<cr><lf>
NSV,13,00,000,00,0.0,00.0,00,00,D<cr><lf>
NSV,4,00,000,00,0.0,00.0,00,00,N<cr><lf>
NSV,25,00,000,00,0.0,00.0,00,00,N<cr><lf>
NSV,0,00,000,00,0.0,00.0,00,00,N<cr><lf>
NSV,11,00,000,00,0.0,00.0,00,00,D<cr><lf>
NSV,0,00,000,00,0.0,00.0,00,00,N<cr><lf>
&


Description Form Field
Start Chars"$"0
UTC of position fixZDA,hhmmss.ssss,dd,mm,yyyy1
Latitude in Degrees/Minutesllll.lllll2
Direction of Lat(N or S)3
Longitude in Degrees/Minutesyyyy.yyyyy4
Direction of Lon(E or W)5
Number of SVsNSV6
Sat. i.d. numberNSV,n,…7
Repeated for “n” sats
End Character“&”



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$ 270 as of August 2007. [1] However, much of it has been reverse-engineered from public sources and is available in references like gpsd, Glenn Baddeley's and Dale DePriest's.

Vendor extensions

Most GPS manufacturers include special messages 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.

Software Compatibility

NMEA 0183 GPS compliant software:
  • NetStumbler
  • Rand McNally StreetFinder
  • Magic e-Map

See also

References

External links

anemometer is a device for measuring wind speed, and is one instrument used in a weather station. The term is derived from the Greek word, anemos, meaning wind.
..... Click the link for more information.
gyrocompass is a compass that finds true north by using an (electrically powered) fast-spinning wheel and friction forces in order to exploit the rotation of the Earth. Gyrocompasses are widely used on ships.
..... Click the link for more information.
Global Positioning System (GPS) is the only fully functional Global Navigation Satellite System (GNSS). Utilizing a constellation of at least 24 medium Earth orbit satellites that transmit precise microwave signals, the system enables a GPS receiver to determine its
..... Click the link for more information.
American Standard Code for Information Interchange (ASCII), generally pronounced ask-ee IPA: /ˈæski/ ( [1] ), is a character encoding based on the English alphabet.
..... Click the link for more information.
In telecommunications and computer science, serial communications is the process of sending data one bit at one time, sequentially, over a communications channel or computer bus. This is in contrast to parallel communications, where all the bits of each symbol are sent together.
..... Click the link for more information.
In telecommunications, RS-232 (Recommended Standard 232) is a standard for serial binary data signals connecting between a DTE (Data terminal equipment) and a DCE (Data Circuit-terminating Equipment). It is commonly used in computer serial ports.
..... Click the link for more information.
RS-423 is a standard for serial communications, similar to RS-232. It was used on the BBC Micro computer with a 5-pin DIN connector. There is no common pinout for RS-423.

Sources

  • Linked Wikipedia articles
  • External links

External links


..... Click the link for more information.
checksum is a form of redundancy check, a simple way to protect the integrity of data by detecting errors in data that are sent through space (telecommunications) or time (storage).
..... Click the link for more information.
exclusive disjunction, also called exclusive or, (symbolized XOR or EOR), is a type of logical disjunction on two operands that results in a value of "true" if and only if exactly one of the operands has a value of "true.
..... Click the link for more information.
newline (also known as a line break or end-of-line / EOL character) is a special character or sequence of characters signifying the end of a line of text.
..... Click the link for more information.
NMEA 2000 is a combined electrical and data specification for a marine data network for communication between marine electronic devices such as depth finders, chartplotters, navigation instruments, engines, tank level sensors, and GPS receivers.
..... Click the link for more information.
baud (pronounced /bɔːd/ unit symbol "Bd"), is a measure of the symbol rate, the number of distinct symbol changes (signalling events) made to the transmission medium per second in a digitally modulated signal.
..... Click the link for more information.
gpsd is a daemon that receives data from a GPS receiver, and provides the data back to multiple applications such as Kismet. It is commonly used on Linux systems. Originally written by Remco Treffkorn with Derrick Brashear, then maintained by Russell Nelson [1] , and now
..... Click the link for more information.
American Standard Code for Information Interchange (ASCII), generally pronounced ask-ee IPA: /ˈæski/ ( [1] ), is a character encoding based on the English alphabet.
..... Click the link for more information.
Global Positioning System (GPS) is the only fully functional Global Navigation Satellite System (GNSS). Utilizing a constellation of at least 24 medium Earth orbit satellites that transmit precise microwave signals, the system enables a GPS receiver to determine its
..... Click the link for more information.
In telecommunications and computer science, serial communications is the process of sending data one bit at one time, sequentially, over a communications channel or computer bus. This is in contrast to parallel communications, where all the bits of each symbol are sent together.
..... Click the link for more information.


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