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Nmea 2000 Connector Pin Assignment

NMEA 2000 connector pinout - Smart!

Today my attention fell to this diagram in a NMEA 2000 device manual from Maretron:


As you can see the pin-out is:

Pin 1Shield-Shield
Pin 2RedNET-S+12V
Pin 3BlackNET-C0V
Pin 4WhiteNET-HCAN-H (data high)
Pin 5BlueNET-LCAN-L (data low)

I noticed that the center pin is not carrying ground or even shield, which I naively thought would be the case. In fact the designers of this pin-out were a lot smarter! As this is a circular connector, a dumb user could theoretically try to push two connectors together whilst forcing a wrong orientation. That would force power down the wrong wires.

Let's see what happens if you rotate the connectors:
FemaleMale 90° Male 180° Male 270°
Shield+12V0VCAN-H>
+12V0VCAN-H>Shield
0VCAN-HShield+12V
CAN-HShield+12V0V

The chosen layout ensures that there is no case where both +12V and 0V are connected at the same time to the two data connections, so if you are really obnoxious and try to ram a connector the wrong way into the T socket the worst that will happen is that the fuse will blow. Once you remedy the situation and replace or reset the fuse the entire system should come back up unharmed. That is Really Cool!

Three Generations of NMEA-2000 Connectors and the E-TEC

Evinrude was the first outboard engine manufacturer in the USA (and probably in the world) in c.2005 to have an outboard engine with NMEA-2000 capabilities. They were innovators in the outboard engine industry in bringing to it the modern world of digital network instrumentation. When NMEA-2000 was being added to Evinrude E-TEC engines, the standards for wiring devices for NMEA-2000 were not particularly set in concrete. As a result, there has been an evolution in NMEA-2000 wiring devices associated with the E-TEC. There are three generations.

The first generation of NMEA-2000 wiring devices for E-TEC engines used Deutsch connectors, a unique multi-connector hub and power inserter, and special Data Harnesses or cables. This wiring was used until c.2005.

The second generation of NMEA-2000 wiring devices for E-TEC engines used a proprietary blue plastic connector with a bayonet-type latch, mostly known as a LowranceNET BLUE connector. This wiring was used on Lowrance and Evinrude-branded I-Command gauges, network wiring devices, and cables. Lowrance was already using, and continues to use, multi-pin connectors of this type for their power, data, and transducer connectors. They used a variant for the NMEA-2000. These were in use c.2005 until c.2008.

The third generation of NMEA-2000 wiring devices for E-TEC engines use the standard DeviceNET Micro connector, also know as the LowranceNET RED connector (although the actual color changed to BLACK from RED after a short time). This change began in c.2007. The DeviceNET Micro connector is now the standard NMEA-2000 connector for smaller networks, and it is used by many manufacturers for their NMEA-2000 device connectors and cables. These DeviceNET connectors began to be common after c.2008.

At the actual E-TEC engine itself, Evinrude used another connector for the NMEA-2000 port, a four-pole Amp-Seal connector. Specialized cables were needed to connect the E-TEC to the network backbone, no matter what sort of wiring was used on the backbone. This changed just recently in the 74-degree V6 E-TEC engines; those engines now use a standard DeviceNET Micro connector for their NMEA-2000 port. A standard DeviceNET extension cable can be used to make a drop cable from the network to an E-TEC 74-degree V6 engine.

In field use it occurs sometimes that a legacy device with the older style wiring of NMEA-2000 is to be maintained and used with newer devices. This can be done in two ways:

--if there is only one legacy device, convert the backbone to the DeviceNET wiring, and make one adaptor cable for the one legacy device so that it can connect to the DeviceNET backbone;

--if there are several legacy devices, split the network backbone wiring into two segments, one with the DeviceNET wiring and a second with the legacy wiring. In this way you can continue to use legacy devices and your legacy wiring components in the legacy wiring segment, while you can add new devices to the DeviceNET segment of the backbone. You still only need to make one adaptor cable if you segregate all the legacy devices onto one segment of the network. The adaptor cable will be inserted in the network backbone.

Wiring of the NMEA-2000 network with pre-made cables and connectors is not mandatory. You can cut off all the cable and run the network backbone wiring on terminal strips, if you like. The pre-made connectors are handier to work with. To make an adaptor, you can typically just cut in two an existing cable of one type, and splice one part of it (that has the necessary connector) onto a DeviceNET cable (which you have also cut in two) with the appropriate connector.

Typically all extension cables on the network are arranged with a male-gender connector at one end and female-gender connector at the other. This allows daisy-chaining of cables. The standard practice is for a network device to have a connector with pins. The network backbone wiring device connection will be a female gender. This is proper because there is power on the network backbone, and, in general, connections that are the source of power do not have pins; this avoid having an exposed connection with a voltage on it. The extension cables connect the device to the network, or extend the network between wiring devices.

The network backbone also typically has a male-female gender pairing. This means the connectors on the backbone with pins will have power on them. One way to avoid exposing these pins with power on them is to locate the power connector at the end of the backbone. Put a termination on the power node T-connector that has pins. Then the connector that is providing power to the network will be female, and no voltage will be exposed on any downstream connector with pins. An alternative method is to use a special power T-connector that has all female connectors. The standard network T-Connectors are used, but both terminators must be male-gender.

There seems to be very good adherence to the wire insulation color codes in all cables I have examined. This means that when making adaptor ables, the wires can be connected based on color.

In a NMEA-2000 cable, the conductor insulation colors should follow the NMEA guidelines, as follows:

RED = network power source (+ 12-VDC)

BLACK = network power common (0-VDC)

BLUE = CAN data signal Low

WHITE = CAN data signal High

Bare Wire = shield or drain ground

Compare at: http://www.nmea.org/Assets/2012%20ibex%20full%20%20nmea%20installation. pdf

For the old Deutsch six-pole connectors that Evinrude (then Bombardier) used for NMEA, the conductors in the cables may not be color-coded; the wire insulation may be just WHITE for all conductors. In that case, you can deduce the signal on the wire from the pin assignment in the Evinrude Deutsch six-poleconnector, as follows:

PIN 1 = CAN data signal HIGH

PIN 2 = CAN data signal LOW

PIN 4 = network power source (+12-VDC)

PIN 5 = network power common (0-VDC)

Compare at:

http://continuouswave.com/whaler/reference/NMEA2000/ I-CommandInstallation.pdf

There might be a shield or drain conductor, too. I have not looked closely at one of these connectors and cables in many years.

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