NMEA 0183 vs 2000: What's the difference?

[JDCAVE]

5 years into boat ownership and I’m still hazy on this topic. I know they use different cabling etc, but am uncertain as to many of the differences. Googling the question, and I found this review.

NMEA 0183 is somewhat intuitive to me. NMEA 2000 is not. Does NMEA 2000 do everything it is cracked up to do? I’m not certain it does. I know some on this forum have had some frustrating experiences with it.

https://www.marineelectronicsjournal.com/content/newsm/news.asp?show=VIEW&a=149

Jim

 

[JDCAVE]

Another article covering this:

https://www.actisense.com/difference-between-v1-5-and-v2-0-of-nmea-0183/

I had Actisense on my boat. I have since discontinued it when installed the Nemo Gateway.

 

[DDW]

They are light night and day. NMEA 0183 is a simple protocol on top of RS232 signalling, slow and one direction. NMEA 2000 is a complicated protocol extension of CanBus, which is a bi-directional multidrop (many devices talking and listening on the same wire) network. It's like comparing a dial up modem to ethernet.

Most cars and industrial controls built in the last couple of decades are based on CanBus. It is very reliable and robust, BUT - also difficult to debug when something goes wrong, without specialized equipment. In a car or CNC milling machine, the whole installation has been designed, tested, etc. In a boat you are more likely to be building it ad hoc from different manufacturers, easier to get something wrong. If you stick to one that has bought into the standard (like Raymarine) most stuff just plugs together. I've got 5 or 6 manufacturers stuff running on the sailboat, it wasn't that much trouble, just follow the rules.

In today's boats, there is so much data moving between so many devices that NMEA 0183 is hopeless. Even NMEA 2000 is being abandon for higher data rate devices, mostly for cat5 ethernet.

Long ago I worked for Intel designing some of the first CanBus chips.

 

[questionmark]

There is a really handy NMEA2K library for arduino. You can find the canbus interfaces on aliexpress for under $2, and build a gateway for cheap. I’ve managed to build my own little network in “the lab” for eventual integration into the boat network.

If I can do it, anyone can. Once I got the gist of the differential signaling then it all made sense.

 

[twistedtree]

They are light night and day. NMEA 0183 is a simple protocol on top of RS232 signalling, slow and one direction..

One nit if I may. Current NMEA 0183 is based on RS 422, not RS 232. They are quite different and incompatible other than by luck.

NMEA 2000 has improved, but there are still a lot of points of incompatibility and/or fundamentally different approaches to the “standard” by different vendors. It works when it works, and doesn’t when it doesn’t. And it’s not always evident which is happening. I’m working with a guy now where one device seems to stop when another is present. This sort of thing would never be tolerated in the computer world, but in NEMA, even after 18 years, it’s still prevalent. Sigh.

 

[diver dave]

0183. When i last read the spec in1991, is 4800 baud neither rs422 or 232 on the physical layer. It is designed to be close to 5 v for a tx hi driving a rx optocoupler for rhe load.

 

[HenryD]

I am baffled how NEMA2K is the "current" standard and yet it has so many limitations. The whole idea of terminators and having nodes conflict with other devices seems so 1980s and like 10base2 vs current Cat5/6 networking.
I had a discussion with a Garmin tech about how much data was on the network from the radar and now cameras, trying to justify some of the proprietary connections, etc. I asked him why he felt that was significantly different than my data network with streaming TV, videos, music, weather and alarm system. He just shrugged.

 

[diver dave]

I am not hopeful that boaters will ever splice fiber, but optical ethernet is a nice solution. No EMC worries, no corroded connections. Stuff i design now has FO 100Mb. But alas, not for the boating market.

 

[gsholz]

NMEA 2k has a certification program to ensure interoperability. They insist that one should only buy NMEA 2000 certified products, not NMEA "compatible" products which is open to a vendor's interpretation. So, if I stick with "certified" products, do I avoid the interoperability issues?

 

[JDCAVE]

NMEA 2k has a certification program to ensure interoperability. They insist that one should only buy NMEA 2000 certified products, not NMEA "compatible" products which is open to a vendor's interpretation. So, if I stick with "certified" products, do I avoid the interoperability issues?

I can’t answer that. What is interesting is that according to the first link above, large commercial ships stick with N-0183. I have a mix of both on my boat, but moving N-0183 into N2K with the Actisense converter is not necessarily seamless.

Jim

 

[diver dave]

NMEA 2k has a certification program to ensure interoperability. They insist that one should only buy NMEA 2000 certified products, not NMEA "compatible" products which is open to a vendor's interpretation. So, if I stick with "certified" products, do I avoid the interoperability issues?

IEC standard 60945 describes the testing regimen in quite detail.

vibration, shock, high temperature, RFI to 10V/m to 2GHz, special emission limits in the VHF marine band, salt spray tolerance, oil resistance, solar resistance (for exposed equip), and dozens more.
If you are considering NMEA2k equipment, ask to see the compliance summary. You have every right to get a copy of the summary.

0183 is simple and robust (if you don't bust spec and drive 3 units with one signal, for example)
2k is fast, has built in error detection and retrys, but it is complex and demands a much higher level of host processing. The actual physical layer IC's are now under fifty cents, driven way down by automotive volumes.
Now able to support 1M bps, but the total bus length goes down, I want to say about 20 meters. It is also not rated for a "star" topology. Its a linear bus, with nodes coming off.

Of course "fast" is relative. CAN is not the correct solution for real-time video work, radar, sonar, etc. Ethernet still king there.

 

[DDW]

One nit if I may. Current NMEA 0183 is based on RS 422, not RS 232. They are quite different and incompatible other than by luck.

True, uses 422 signal levels though few devices are actually differentially driven and very few use the multidrop capability. 232 an 422 are Tweedledee and Tweedledum compared to 2000.

The advantage of 10bt type ethernet topology is that as a star network, one node is much less likely to screw the entire network, as it can in a daisy chain.

 

[diver dave]

422, 423, and 232 are only physical layer descriptions, no protocol speced. NMEA 0183, Ethernet, NMEA2k include the physical layer plus a number of ISO stacks above that.

422 is not the basis for 0183, although there is some haphazard compatibility. 423 is probably closer. 422 is true differential, resulting in +4, and -4 V as read by a floating oscope. 0183 is +4 and zero....
Sooo, the 0183 simply ignores the -4. 0183, again, drives a digital optocoupler on the Rx side, which is unidirectional.

 

[twistedtree]

NMEA 2k has a certification program to ensure interoperability. They insist that one should only buy NMEA 2000 certified products, not NMEA "compatible" products which is open to a vendor's interpretation. So, if I stick with "certified" products, do I avoid the interoperability issues?

No, it definitely does not guarantee interoperability. I have encountered many devices that don't interoperate in one way or another, and they are all NMEA certified. Certification means almost nothing.

 

[diver dave]

No, it definitely does not guarantee interoperability. I have encountered many devices that don't interoperate in one way or another, and they are all NMEA certified. Certification means almost nothing.

Proper install is also important.

Both bus ends terminated with the correct resistor value, and NOT terminated anywhere else?

Maximum bus length not exceeded? Maximum node length not exceeded?

 

[twistedtree]

Proper install is also important.

Both bus ends terminated with the correct resistor value, and NOT terminated anywhere else?

Maximum bus length not exceeded? Maximum node length not exceeded?

Agreed that's all important.


All the issues I encountered were application layer (PGN messages) where the sender and receiver had different views/interpretations of how the contents should be filled out and interpreted. Also devices that don't implement mandatory features. And devices claiming to be things they are not, like an iCOM M506 claiming be a GPS device and consequently messing up other devices who believed it. And companies that take fundamentally different approaches to performing data source selection. And converters that don't do any data source selection and translate all data from all devices into one big jumbled mess.


NEMA certification doesn't look at any of that. My Blog has a whole section (the wall of shame) on the issues I have encountered, many of which have never been fixed by the manufacturers.


When N2K works, it's great. My biggest frustration is that it could be so good, but isn't because vendors haven't made it a priority to ensure interoperability. Adding a new device to an N2K network is a little like installing new software on a windows machine. It's a crap shoot whether the software will work, and there is a distinct chance it will disable your whole system. This is why lots of people, me included, are still running XP and don't want to touch it. And it's why only 0183 is allowed in IMO boats.

 

[diver dave]

TT; Keep up the good detective work. It's obviously a minefield out there for the N2k users at all levels.
The more negative hits one gets during equipment searches on-line, the more likely the manufacturers will get their act together. At least, hopefully. In the meantime, it appears the big players are playing a game to enforce a single vendor solution, so the can "lock you in".

And NMEA, who knows. Steve Spitzer (director of standards) seems to be reacting to field issues, per the 2016 conference. Sounds like it is still a flail.

If NMEA is not careful, someone else may take this over with a better plan. They do not own Canbus, so a clever person could set up shop and really do the specs and qualification plan correctly.

 

[wkearney99]

There's many issues to be considered and 'twistedtree' highlights on of the biggest hassles... message contents.

Too many of the devices only rise to a certain level of performance. They only interpret 'some' of the data, and not always in a way that makes sense for anything other than their very limited intended implementations. As in, it looks like it ought to be good for X, Y and Z but the vendor really only designed it to do A, B and C. Note, no overlap. Customers/installers naively believe the marketing literature and chaos ensues. To make matters worse some vendors truly believe their device 'works' but have never actually tested it in anything other than their development situations. Leaving the customers to be nearly alpha testers in the field.

There's really no other market that compares to recreational boating. It's a small market compared to other things like cars, trucks, RVs and the like. Meaning there's not a lot of target customers. Nor are there a lot of 'professional' installers. That and many of the vendors really don't seem to put much energy into doing a thorough amount of interoperability testing with those from other vendors (or any testing, really).

 

[twistedtree]

TT; Keep up the good detective work. It's obviously a minefield out there for the N2k users at all levels.
The more negative hits one gets during equipment searches on-line, the more likely the manufacturers will get their act together. At least, hopefully. In the meantime, it appears the big players are playing a game to enforce a single vendor solution, so the can "lock you in".

And NMEA, who knows. Steve Spitzer (director of standards) seems to be reacting to field issues, per the 2016 conference. Sounds like it is still a flail.

If NMEA is not careful, someone else may take this over with a better plan. They do not own Canbus, so a clever person could set up shop and really do the specs and qualification plan correctly.

There was a lot of hope that SignalK might rise to the occasion as an open alternative to N2K, but by all appearances it has been a total flop.


And I agree that the vendors don't appear too motivated to fix the issues. I have had engineers from different companies on the phone individually discussing an interoperability problem, and offered to introduce them to each other so they can sort things out. Neither had an interest. Go figure.


But after nearly 20 years, I've come to accept that it is what it is, and it isn't going to get much better. So I use it where it can be shown to work, and otherwise use 0183 for primary, critical systems.

 

[wkearney99]

The trouble with falling back to 0183 is there aren't sentences for a lot of new data. Sure, for what's supported it has utility but for new stuff? Not so much.

Having worked on standards bodies myself I can tell you it's messy. Way too many short-sighted, short-term 'land grabs' by some developers/vendors. Risks include dominant players hijacking the standard with incomplete/inferior or otherwise limited approaches. Lots of junior players then straggle along behind that and the process breaks down/loses momentum. Then the half-assed implementation becomes a 'defacto' standard, making an even bigger mess. At least 2K seems to be avoiding that, but still seems to have a lot of half-assed implementations.

What really makes it a mess is their arrogance regarding publishing the documentation. I mean, really, what's the goal there? Protecting the incredibly limited market is about the only excuse I can fathom (beyond the utterly ridiculous goal of trying to pay for the standardization effort/committee). Put it out there, get people making a go of it.

 

[George Harmon]

https://www.marineelectronicsjournal.com/content/newsm/news.asp?show=VIEW&a=149

http://www.nmea.org/Assets/2012 ibex full nmea installation.pdf

https://www.maretron.com/products/pdf/Network Installation Guide.pdf

 

[JDCAVE]

George: there’s a problem with the link to the Maretron Page. I must say the NMEA website could do with an upgrade!

Well, I got exactly what I wanted from this thread: a civil discourse on the issues involved. If people such as TT have problems with N2K, how can the rest of us deal with it? Many of us here have a mix of new and old electronics from different manufacturers. They work well for their intended purposes and I’m blowed if I’m going to replace equipment just so I can get the latest and greatest and be fully N2K. I just want the info from my various devices displaying on my Coastal Explorer screen. Fortunately the Nemo Gateway helps me achieve that.

Jim

 

[George Harmon]

George: there’s a problem with the link to the Maretron Page. I must say the NMEA website could do with an upgrade!

Well, I got exactly what I wanted from this thread: a civil discourse on the issues involved. If people such as TT have problems with N2K, how can the rest of us deal with it? Many of us here have a mix of new and old electronics from different manufacturers. They work well for their intended purposes and I’m blowed if I’m going to replace equipment just so I can get the latest and greatest and be fully N2K. I just want the info from my various devices displaying on my Coastal Explorer screen. Fortunately the Nemo Gateway helps me achieve that.

Jim

Try here: https://www.maretron.com/products/pdf/Network Installation Guide.pdf

 

[JDCAVE]

Thanks for that George: One point in that document caught my attention.

“1.4 Maximum Drop Line Length. The maximum cable distance from any device on a branching drop line to the trunk line is 6 meters (20 feet).” I’m pretty sure my Airmar PB 200 weather station cable exceeds that length.

 

[wkearney99]

Well, I got exactly what I wanted from this thread: a civil discourse on the issues involved. If people such as TT have problems with N2K, how can the rest of us deal with it?

Approach it for what is it, a network system. It's not just 'wires'. It's designed to be flexible in configuration but has a number of specific configuration requirements. Ignore those at your peril. Lots of times people make assumptions about things and that leads to problems.

Users making leaps, "because you can do X, you therefore must be able to do Y" kind of problems. "I ought to be able to do x, y and z and if I can't then that means the manufacturer is a stupid idiot." Or is somehow out to cheat them or force them into buying some expensive doo-dad. Which they don't understand and thus is must be unnecessary.

I'm not casting aspersions toward anyone here, of course. Just tossing out generalizations that all of us might do well to consider.

 

[George Harmon]

Thanks for that George: One point in that document caught my attention.

“1.4 Maximum Drop Line Length. The maximum cable distance from any device on a branching drop line to the trunk line is 6 meters (20 feet).” I’m pretty sure my Airmar PB 200 weather station cable exceeds that length.

The trunk line can be very long lengths, from one end of the vessel to the other. Perhaps the trunk line (backbone) could be routed closer to the distant equipment. I don't have much expertise on the subject as I am trying to learn enough to convert some old Raymarine components to newer 2K equipment.

 

[twistedtree]

Just to be clear, I don't mean to discourage use of N2K. Personally I use it quite a bit, but primarily for monitoring, and also for backup navigation.



What I DO want to encourage is that people go into it eyes wide open. Check your configuration, check your wiring, check for reported errors (many devices have diagnostic pages where they report bus errors), and don't ignore odd behavior because it's almost always symptomatic of a problem.

 

[wkearney99]

News on the fleet vehicle front:
Simulating SAE J1939 PGNs Used By Truck & Bus FMS (Fleet Management System) Standard - Copperhill