Question for fairdeal

[boscoe99]

What is all of this talk of J1939 about? Seems that it is just more or less a part number for a cable.

Is it specific to Garmin?

[fairdeal]

What is all of this talk of J1939 about?

Is it specific to Garmin?

I believe so.

You probably know J1939 is like "NMEA 2000 for diesel trucks buses and trains" -
although it came first -
the NMEA 'copied from it' for NMEA 2000;

publishing this is 1999:





So modern "marinized" diesel engines use J1939, but apparently because the market is small,
have been largely ignored by the recreational electronics manufacturers - Furuno, Simrad, Garmin etc.

However, about 3 years ago, Garmin offered a "J1939 capable" version of their GPSMAP 7000 series MFD -
and later included it as standard - in addition to NMEA 2000 capability -

so on some Garmin MFDs, there are two identical DIN connectors,

one labeled NMEA 2000, the other J1939.


The reason we are hearing about it now -

for some unexplained reason,

when Yamaha allowed Garmin, Furuno and Simrad to 'emulate' the Command Link display -

Furuno and Simrad did it via the Yamaha "Gateway" to a NMEA 2000 backbone

(and of course a software update)

but Garmin chose to require connection to that 'J1939' plug in order to enable the emulation.

(and maybe also need a Yamaha Gateway - but I don't recall - it confuses the sh*t out of me)

[boscoe99]

Thanks. Certainly is causing confusion amongst the users.

[boscoe99]

Do the new Garmin's only have a J1939 port?

If so, will they receive both Command Link and Command Link data directly from an applicable CL or CL+ hub?

[fairdeal]

At this point, all Garmin marine plotters (except their 4" unit) have a NMEA 2000 port -
but only a few have, in addition, the J1939 port.

Sadly, regarding documentation of the Yamaha "emulation screen" -
they have mirrored Yamaha's style: murky, and incomplete.

The Garmin documents:
- specify that the J1939 port must be used to get the Yamaha screen
- specify that their cable goes from the J1939 port "to the Yamaha hub" (via a Yamaha pigtail cable)
- do not indicate that a Yamaha Gateway is required in between
- do not reference any distinction between whether the Yamaha hub is CL or CL+

So it would seem, that the J1939-equipped Garmins will display the Yamaha screen
when directly connected to either CL or CL+

But I have no way to be 100% certain;
unfortunately,
I purchased my current Garmin MFDs before the J1939 port was added to those models -
so I am unable to get empirical data.
(and lack access to a DEC engine, anyway)

[boscoe99]

Thanks. This is getting a tad less fuzzy to me thanks to your help.

I think that the emulation of the Yamaha display is what is driving this. Versus seeing just engine data in a number of other ways. J1939 to see data in the Yamaha CL+ format versus seeing data in a non-Yamaha CL + format via NMEA 2000.

Aren't you thinking that you really really need a new Garmin display? One with a J1939 port? And while you are buying it, isn't it time for you to have a new Yamaha DEC model so that you have both CL and CL+ ports available?

[boscoe99]

The configuration of the NMEA 2000 receptacle and the J1939 receptacle look identical. Is the wiring different?

[boscoe99]

What might happen if a Lowrance 0120-37 cable that is connected to a Yamaha engine gets connected to the J1939 receptacle?

[fairdeal]

The configuration of the NMEA 2000 receptacle and the J1939 receptacle look identical. Is the wiring different?

Identical - both "Micro-C" connectors - and the pinout is the same.


So the only difference between "the Lowrance Cable"

and Garmin's "Yamahaź Engine Bus to J1939 Adapter Cable" :

- Lowrance uses a female Furukawa plug - so it can directly connect to a Yamaha "Device" port or engine harness plug

- Garmin uses a male Furukawa plug - so you need a Yamaha "pigtail cable" to use it

(obviously Garmin deferred entirely to Yamaha in the design of the cable!)



from J1939 section of a Garmin Installation Manual:





Standard NMEA 2000: