NMEA Guide
Contents
1. OOO 0 dap Compass Radar Instruments Instrument bus eg Seatalk page 3 of 3 Issue 1 0 22 07 20032. boat equipment which can be done via the RS232 serial ports The standard RS 232 connector is a 9 pin plug Serial Port Connections Pin Signal Connect To 2 Rx Data lt NMEA Out Data 3 Tx Data gt NMEA In Data 5 Signal ground NMEA In Out Common To connect your PC to external equipment you need to make up a serial cable with a 9 pin plug one end and bare wires the other end The bare wires go to the NMEA In Out terminals on the navigation equipment and the plug end goes to the PC RS232 Rx Data RS232 Tx Data RS232 Signal Ground a NMEA Out Data NMEA Out Common NMEA In Data NMEA In Common 9 Pin Serial ANRA TPE Use of a PC isn t limited to charting you can use your PC as a SatC terminal use it to send and receive emails via your SSB or Satcom as well as display instrument data on screen Make sure you thoroughly read the instructions that come with the software and the equipment you want to interface some require that external equipment is connect ed via a specific serial port for it to work page 2 of 3 Cactus Troubleshooting There are generally five reasons why NMEA interconnection isn t working I talk NMEAO183 version 3 0 Same language different dialect 1 Different NMEA formats versions NMEA data is available in three formats NMEAO180 NMEAO181 and NMEAO183 although only very old equip ment outputs receives in 0180 or 01
3. 81 format all current equipment is NMEAO183 compatible However even NMEAO183 is available in different versions the latest is NMEAO183 version 3 0 When interconnecting two pieces of equipment ensure that both are set to the same for mat version 2 Sentence incompatability Just because two pieces of equipment are NMEA compati bly doesn t mean they re necessarily saying listening for the same thing Connecting a depth sounder to a radio isn t going to produce any kind of useful co operation because the radio isn t interested in what depth sounder is out putting Check the user manual of both products to see which NMEA sentences they are transmitting and receving If you want to plug your GPS into your chart plotter you need to make sure that the plotter can recognise at least some of the sentences the GPS is outputting Also bear in mind that some sentences contain more data than others if you link your radar to a compass but the radar will only show mag netic heading even though the compass can also show true data it s probably because the NMEA heading sen tence both units understand doesn t include true data 3 Incorrect wiring There are only two wires involved how difficult can it be Well although you can t do any damage if you get the wires the wrong way round the major problem with NMEA inter connection is that there is no set reference standard with regarding to NMEA connections the two wires can be any col
4. atus A OK V warning unit from an external O by the unit going out to 0 66 L Cross track error nautical miles steer Left to correct source e eco another unit 003 Origin waypoint ID 004 Destination waypoint ID F 4917 24 N Destination waypoint latitude 49deg 17 24min N some units may have a special NMEA lead supplied others 12309 57 W Destination waypoint longitude 123deg 09 57min W may Just be screw terminals and you have to supply your 001 3 Range to destination nautical miles own cable Pretty much any standard two core cable will 052 5 True bearing to destination work fine Reading the various user manuals you will then 000 5 Velocity towards destination knots p i Toe 2 find that there is little consistency when it comes to refer V Arrival alarm A arrived V not arrived ences for the NMEA connections some talk about NMEA This shows the amount of data that can be contained in an Data and Common others NMEA and or even NMEA A NMEA0183 sentence It might look complicated but you and B Whatever they call them you basically have a wire don t need to worry in reality you re never going to see that supplies data plus a return wire Don t be distracted the information expressed in this way all equipment made by the wire colours of any cable that might come with the today automatically processes the data and displays it on unit there is no colour standard for NMEA cables and it screen in a usable format wi
5. ion received through the NMEA In port directly to the NMEA Out port So if for example you want Lat Long and compass data feeding into your radar which would normally mean two NMEA In connections from a GPS and a Compass instrument if may be that both items of data can be supplied by connecting the GPS to the Instrument System NMEA In port and the radar to Instrument s NMEA Out port which will supply compass data from the fluxgate instrument plus echoed Lat Long data from the GPS GPS NMEA Out gt gt gt gt gt Lat Long data Instruments NMEA In NMEA Out _ NMEA In gt gt gt gt gt Compass data plus echoed Lat Long data pi h 5 NMEA not turned on It could be as simple as this not all equipment automati cally outputs or reads NMEA Check both units for an NMEA setup page and if NMEA In Out has been turned on Cactus If all else fails Sometimes no matter what you do or what appears to be possible in theory connecting two units together via NMEA just won t work There could be a number of reasons for this and it doesn t necessarily mean that either unit is faulty in any way To avoid any disappointment talk to the experts at Cactus who will be able to advise you about the best equipment to buy and how to interconnect them to get the results you re looking for Examples of common links Chartplotter GPS on NMEA Out NMEA In GPS OOO NMEA Out NMEA In
6. ll vary depending on the manufacturer and which cable they are using Making it work If you want to be able to connect two pieces of equipment IMPORTANT You need to connect the NMEA OUT termi together you first need to establish that they are going to nals of the talking unit to the NMEA IN terminals of the talk to each other They may both be NMEA compatible listening unit but most equipment only transmits or receives a relatively page 1 of 3 Issue 1 0 22 07 2003 technical guides TANAYAYATAN IST nn GUIDE TO NMEA ctd What you can can t do with NMEA NMEA interfacing allows two pieces of equipment to share simple data such as boat speed course and current posi tion expressed as Lat Long What it can t do is transfer large or complex items of data For example connecting a chart plotter and a radar together may allow the radar to read course and position data from the chart plotter or the chart plotter can plot a position based on a mark placed on the radar but the radar wouldn t be able to download a chart picture from the plotter via NMEA and the plotter couldn t display a radar image For large amounts of data like this you need a high speed data link such as Raymarine s HSB2 system or Furuno s Navnet Connecting to a PC With PCs and laptops becoming a more common feature on boats and with a whole range of navigational software avail able on the market it is useful to be able to connect a PC to your
7. on and communication Electronics radar A fishfinder or sonar is more likely to beable to l receive NMEA depth data manufacturers have their own proprietry protocols such as SeaTalk and HSB2 from Raymarine which would normally The next thing you need to check is that both units under limit interaction to equipment made by the same manufac stand the same NMEA format It s not enough that they re turer but NMEA compatibility means that critical information both NMEA0183 compatible it needs to be the same ver is translated into standardised NMEA data sentences which sion of NMEA0183 A lot of equipment gives you the can be understood by any other equipment set up to read option to select version 1 5 2 0 or 3 0 the same sentences Thus your Garmin GPS can provide position data to your Raymarine chart plotter which in turn can send course data to your Simrad autopilot Then you need to check the connections If you want the unit to talk to another piece of equipment you want to look for a port labelled NMEA OUT If you want the unit to listen to data from another piece of equip ent look for the What does NMEA data consist of NMEA IN port This is an example of a typical NMEAO183 sentence output by a chartplotter RMB A 0 66 L 003 004 4917 24 N 12309 57 W 001 3 052 5 000 5 V OB NMEA In NMEA Out T of RMB Sentence name Recommended Minimum Nav Info Data coming into the Data produced or echoed A Data st
8. our and the terminals can be called anything NMEA Data and Common NMEA and NMEA A and B and so on Some manufacturers don t have a dedicated Common terminal in which case you have to connect the common wire from the other unit to the battery negative of the equipment you re interfacing with Issue 1 0 22 07 2003 technical guides TANAYAYATAN GUIDE TO NMEA ctd Then there is confusion with using the NMEA In and Out ports a common mistake made is when people confuse NMEA In and Out with NMEA Data and Common NMEA In and Out refers to the direction the information is going in the In port is listening for data being received from an outside source the Out port is where the unit transmits data to outside equipment Both the In and Out ports each have Data and Common terminals Make sure the wires are going to the right ports NMEA NMEA In Out NMEA In Data 2E E NMEA Out Data NMEA In Common NMEA Out Common 4 Too many sources NMEA format allows for one talker and several listeners in other words at any one time a unit can be receiving NMEA data from ONE other unit and can be transmitting NMEA data out to several other units You can t have two NMEA sources going into one unit unless the unit has two or more separate NMEA In ports There are ways to work around this problem some equip ment particularly chart plotters and instruments echo a lot of NMEA informat
9. technical guides Cactus TANAYAYATAN GUIDE TO NMEA Most marine electronics boast about being NMEA com patible but what does that mean What does NMEA compatibility allow you to do How easy is it to con nect equipment together using NMEA Wir scheinen eine Sprachbarriere zu haben hier Kann jemand mich verstehen iLos saludos Habla usted Seatalk NMEA stands for National Marine Electronics Association which is the US body that attempts to regulate marine elec tronics manufacturers in that country the UK equivalent is the BMEA When equipment claims to be NMEA compat ible what they are actually saying is that they are compliant with the standard communications protocol as defined by the NMEA The protocol has gone through various stages of evolution since it s initial concept but the current version that virtually all marine equipment is compatible with is small selection of sentences relevant to what the equip NMEAO1832 ment is doing So for example a radar will typically be able read Lat Long and Compass data via NMEA because this What is NMEA0183 data can be used to enhance the performance of the radar On the other hand it s unlikely to be able to read water This is a standardised electronic language that enables zo TO depth because this information is ultimately useless to the equipment made by different manufacturers to have a limit us ed level of interacti
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