The NMEA 0183 Information sheet Everything you wanted to know about NMEA 0183 (but were afraid to ask) Understanding the NMEA 0183 specification How to connect NMEA 0183 devices together How to understand NMEA 0183 sentence formats Issue 3
Actisense® Contents Important Notices Notices Feedback! NMEA 0183 Introduction 4 4 4 4 The Actisense product range 8 Connecting NMEA talkers to NMEA Listeners Differential NMEA talker 9 9 The basics Electrical specification NMEA 0183 v2.x and v3.x Talker NMEA 0183 v1.
The NMEA 0183 Information sheet - Issue 3 NMEA 0183 Sentence Format 13 NMEA Contact Information Company Information 16 16 DBT – Depth Below Transducer DPT – Depth MTW – Mean Temperature of Water VHW – Water Speed and Heading VLW – Dual Ground/Water Distance NMEA Version 3 Approved Sentence Formatters © 2011 Active Research Limited 13 13 14 14 14 15 Page 3
Actisense® Important Notices NMEA 0183 Introduction This Actisense document is for informational purposes only, and to the best of our knowledge, the information contained within is accurate and true. Any use of the information contained within this document is solely at the user’s own risk.
The NMEA 0183 Information sheet - Issue 3 Electrical specification The latest specifications for NMEA 0183 (version 2 and onwards) should, as a minimum, meet the requirements of the computer standard “RS422” (Standard EIA-422-A). They use +5 / 0 volt signalling, which is low voltage and easy to interface to computer equipment.
Actisense® NMEA 0183 bus at any one time. To combine data buses, you must use a multiplexer, such as the Actisense NDC. This safely receives the data from multiple talkers, and combines it together into a single stream. Two or more Talkers are simply not possible on the same data line as they are not synchronised to each other, and will attempt to ‘talk’ at the same time (over each other).
The NMEA 0183 Information sheet - Issue 3 The different versions of the NMEA 0183 standard As the NMEA 0183 specification has slowly evolved over the years, connecting one device to another is not always a simple matter. The situation is further complicated, as many manufacturers still use the old (“single ended”) method of connection because it is cheaper to implement.
Actisense® The Actisense product range Actisense produces a full range of products to solve all NMEA interfacing and interconnection requirements, including: PC OPTO-Isolation cables The Actisense PC-OPTO range allows a PC to safely receive data from an NMEA 0183 system, protecting against high voltage spikes and preventing dangerous ground loops.
The NMEA 0183 Information sheet - Issue 3 Connecting NMEA talkers to NMEA Listeners Care needs to be taken when connecting different types of NMEA talkers together, particularly where a mixture of NMEA versions is encountered. These pages show common connections for each type of talker and listener, and how to connect between new type differential devices and old type single-ended devices. On page 10 and 11, details are given for connecting an on board PC system to an NMEA 0183 marine electronic bus.
Actisense® Single-ended NMEA talker These are the recommended methods of connection for a single-ended, pre - NMEA version 2.0 talker. Many instruments that output version 2.0 formatted strings use a single-ended output. This is often the case with some of the hand-held GPS units such as from Garmin, as the circuitry to produce the differential output is more complex, and requires extra connector pins. Single ended outputs are normally labelled ‘NMEA Tx’, ‘NMEA Out’ or just ‘Data’.
The NMEA 0183 Information sheet - Issue 3 Connecting a computer to your NMEA 0183 system A very common requirement now is to connect a PC or Laptop computer to the marine data network. As the NMEA specification basically uses the same asynchronous Comms specification in accordance with ANSI standard as used on a standard PC serial port, most PC’s can read NMEA directly through their Comms port.
Actisense® Testing an NMEA 0183 computer connection with Actisense NMEA Reader NMEA Reader is free software for PC users to easily monitor and debug NMEA data. Capable of displaying both NMEA 0183 and NMEA 2000 data NMEA Reader can be an invaluable tool for installing an NMEA network. NMEA Reader can be found on the software updates page on the Actisense website. Example data using an Actisense talker device By connecting a so-called “Triducer” from a company like Airmar (www.airmar.
The NMEA 0183 Information sheet - Issue 3 NMEA 0183 Sentence Format All NMEA 0183 data is sent in the form of text sentences, each beginning with a ‘$’ or ‘!’ symbol, and use commas to separate each part of the sentence. NMEA codes are plain ‘ASCII’ text, and have the following format: $yyXXX,……… *xx <0D><0A> • The sentence always starts with a ‘$’ or ‘!’ symbol • A 2-digit ‘yy’ code follows, giving the instrument type (e.g.
Actisense® MTW – Mean Temperature of Water Water temperature in degrees centigrade. Format: $xxMTW,DATA_TEMPERATURE_C,C*hh<0D><0A> Example Extended precision, with checksum: $YXMTW,17.75,C*5D<0D><0A> 17.75 degrees centigrade. VHW – Water Speed and Heading The compass heading to which the vessel is currently pointing, and the speed of the vessel through the water.
The NMEA 0183 Information sheet - Issue 3 NMEA Version 3 Approved Sentence Formatters This list shows how the three letter formatters expand into a more meaningful description of the contents of the NMEA 0183 sentence. To discover the contents of the actual sentences, you must purchase the standard from the NMEA (refer to the NMEA Contact Information).
Actisense® NMEA Contact Information NMEA - National Marine Electronics Association 7 Riggs Avenue Severna Park, MD 21146 USA Telephone: Fax: +1 (410) 975 9422 +1 (410) 975 9450 E-mail: Website: info@nmea.org www.nmea.org Company Information Active Research Limited 5, Wessex Trade Centre Ringwood Road Poole Dorset UK BH12 3PF Telephone: 01202 746682 (International : +44 1202 746682) Actisense on the Web: For advice, support and product details E-mail: Website: support@actisense.
