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Author Topic:   NMEA-0183 Interface
jimh posted 02-20-2013 10:11 AM ET (US)   Profile for jimh   Send Email to jimh  
The National Marine Electronics Association promulgated their 0183 standard for interconnecting marine electronics many years ago. In response to the recent urging of the United States Coast Guard, NMEA has collaborated with equipment manufacturers and the Coast Guard (and others), and is in the process of revising their NMEA-0183 standard to include recommendations for a consistent color coding of conductors carrying NMEA-0183 data in a new NMEA-0183 Version 4.10. These recommendations are only voluntary, and do not carry any force of law. Compliance is expected to be high, but it may take some time to be achieved. For the technically curious, the new color code standard is as follows:

NMEA 0183 Color Code
Name Color Description
Talker A White Data-H
Talker B Brown Data-L
Listener A Yellow Data-H
Listener B Green Data-L
NMEA0183HS C Black Ground
Shield Bare (See standard for special handling)

An interconnection between two devices using this new color code standard is illustrated below:

jimh posted 02-20-2013 01:22 PM ET (US)     Profile for jimh  Send Email to jimh     
The drawing (above) illustrations several important aspects of proper NMEA 0183 interface interconnection.

The shield on the cable carrying the TALKER pairs is only terminated at one end; it is only connected at the TALKER end. At the LISTENER end the shield is unconnected; it floats. This method of handling shielding is very typical in modern differential two-conductor signals.

There are no plus-sign (+) or minus-sign (-) markings or designators used for any signal or wire. Many manufacturers have mistakenly used plus-sign (+) or minus-sign (-) markings on their wiring for NMEA-0183 or in their illustrations of NMEA-0183 or in their narrative text describing NMEAS-0183. But there are not any such plus-sign (+) or minus-sign (-) designators in the actual NMEA-0183 standard. The two, paired signals are called TALKER A and TALKER B or LISTENER A and LISTENER B. In all cases of interconnection you connect an "A" to the corresponding "A" and a "B" to the corresponding "B" signals.

Many people have been misled by plus-sign (+) or minus-sign (-) markings into thinking that NMEA-0183 signals were polarized like DC voltages.

There are not designators for "input" or "output"; the terms used are LISTENER and TALKER. Many manufacturers have in the past invented their own terminology for these signals. There are no designators for "in" or "out"; the terms used are LISTENER and TALKER. Many manufacturers have in the past invented their own terminology for these signals.

The signals are provided in differential pairs. In the past some NMEA-0183 devices used single-ended signals which were referenced to ground. The mixing of differential and single-ended signals made interconnection even more difficult to accomplish. Even reasonably skilled and trained technicians would often make errors interconnecting differential and single-ended signals. The NMEA-0183 standard has recommended differential signals for some time. It is hoped that going forward manufacturers will follow the recommendation and provide differential signals for NMEA-0183.

The illustration omits the NMEA0183 HS signal, carried on a BLACK conductor. As far as I can deduce, this signal is just connected to GROUND, which on a small boat will often be the battery negative bus or a hull bonding bus. I have not seen any further information about handling this signal; if I do, I will append it here.

If the cable of one device has to be extended to reach another device, the color codes used to extend the circuit should retain the color codes of the TALKER circuit.

Chuck Tribolet posted 02-20-2013 04:24 PM ET (US)     Profile for Chuck Tribolet  Send Email to Chuck Tribolet     
Standard connectors would be even better.


jimh posted 04-20-2014 10:31 AM ET (US)     Profile for jimh  Send Email to jimh     
I have added the information from this article regarding the proposed standard for wire colors for NMEA-0183 to my article in the REFERENCE section on NMEA-0183 interconnections. See html#wireColorCode

jimh posted 04-20-2014 05:14 PM ET (US)     Profile for jimh  Send Email to jimh     
Regarding use of a consistent color code for identification of wires carrying NMEA-0183 signals, I have to wonder if adoption of a recommended standard by NMEA at this late in the history of the NMEA-0183 standard will have much effect, particularly how it will affect manufacturers who have been using a consistent color code of their own for many years and across many products. In the long absence of any recommended color code standard from NMEA, some manufacturers have adopted their own standard for wire color. These manufacturers have a substantial amount of product in the field that uses their own color code. To abandon that manufacturer-specific color code and change to a proposed NMEA standard would perhaps cause confusion. A manufacturer would have a large amount of product in use that adheres to one color code standard, and then new product would adhere to a different standard. Having two sets of products following two different color code schemes could cause more confusion among users of those products and support people for those products.

A good example is the use of a BLACK conductor for the negative circuit of a 12-Volt DC power distribution. Recently it was decided that this ought to be changed to YELLOW. There are probably millions of boats with wiring that has the 12-Volt negative circuit running on black conductors. Some guy buys a new boat, looks under the hood, and see all these yellow wires running everywhere. Has the new standard made things simpler, easier to understand, or better? It is hard to say.

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