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====== NMEA 2000 ======

Notes about this standard. Buying it costs 4000 or maybe 8000 USD, if they feel like selling it to you. [[https://web.nmea.org/atlas/forms/general/11|NMEA standard order form]]

===== Data =====

PGNs are what they call message types, or what defines the meaning of the message body. They form part of the 29 bit CAN ID. NMEA200 can carry PGNs from the SAE J1939 standard, used for road vehicles. These messages may come from engines on a boat. Looks like NMEA2000 is actually an extension of J1939, or rather close to it.

[[https://endige.com/2050/nmea-2000-pgns-deciphered/|PGN Binary encoding / CAN address format]]

[[https://web.nmea.org/External/WCPages/WCWebContent/webcontentpage.aspx?ContentID=189|List of some PGNs from NMEA]]

Wireshark, told to decode as J1939, will show the PGNs.

===== Physical =====

See also: [[can_interfaces|CAN Interfaces]].

Physical layer is based on [[https://web.archive.org/web/20070128083016/http://www.odva.org/Portals/0/Library/Publications_Numbered/PUB00026R1.pdf|DeviceNet]] - notably the Micro-C connectors.

==== Cable ====

Cable sold for NMEA 2000 is very expensive. Cable sold for DeviceNet is less expensive but still a lot. Normal ethernet (Cat 5 etc.) cable would probably work. It is 100 Ohm nom., and NMEA 2000 is meant to be 120 Ohm, but it's probably close enough, particularly for short networks as expected on a boat. Calculated SWR of 100 to 120 ohm connection is 1.2 / ~21dB return loss.

Possibly suitable:

  * BELDEN 3084A
  * LAPP KABEL 2170343 - Multipair Cable, Per M, DeviceNet Field Bus, Data Pair 24 AWG+ Power Pair 22 AWG, Screened, 2 Pair
  * MOLEX / FLAMAR 155421-5001 - Networking Cable, Flamar® Profinet Type C, Screened, Cat5e, 22 AWG, 0.34 mm², 328 ft, 100 m

Actisense NMEA 2000: https://www.tcschandlery.co.uk/actisense-micro-nmea-2000-cable-per-metre/p21018

==== Colours ====

| Grey | Shield |
| Red | NET-S Power |
| Black | NET-C Ground |
| White | NET-H  | 
| Blue | NET-L  |

Micro size cables should be Power: 22 AWG, Data: 24 AWG.

==== Connectors ====

"Micro-C". M12, A coded.

[[https://www.farnell.com/datasheets/2634541.pdf|An Amphenol datasheet of NMEA2000 connectors.]]

==== Terminators ====

120 Ohms on each end.

Devices are supposedly required by the standard to NOT contain terminators.

==== Links ====

  * [[https://github.com/canboat/canboat/|CAN Boat - Open source, reverse engineered NMEA 2000 tools]].
  * [[https://canboat.github.io/canboat/canboat.html]]
  * [[https://web.archive.org/web/20210506224409/https://www.nmea.org/Assets/2000-explained-white-paper.pdf|Old but official info]]
  * [[https://www.maretron.com/products/pdf/Network%20Installation%20Guide.pdf]]
  * [[https://actisense.com/wp-content/uploads/2021/08/Complete-Guide-to-NMEA-2000_Revision_4_2021.pdf]]
  * [[https://continuouswave.com/whaler/reference/NMEA2000.html|NMEA-2000 Networks and Modern Outboard Engines]]
  * [[https://www.csselectronics.com/pages/nmea-2000-n2k-intro-tutorial#nmea-2000-vs-j1939-vs-isobus]]
  * [[https://docs.hatlabs.fi/sh-esp32/pages/tutorials/nmea2000-gateway/|hatlabs - manufacturer of open source NMEA gadgets, supplier of connectors and parts]].