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What is NMEA output / data?

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‘NMEA Data’ can be split into 2; NMEA 0183 and NMEA 2000. Whilst there are other, earlier versions of NMEA 0183 (NMEA 0180 and 0182), they are very rarely seen in the field, and their functionality is limited.

From 1992, NMEA released NMEA 0183 2.0, which utilised RS-422 for differential interfacing with two signal wires, however, there are still many devices that use previous versions (1.5 and pre) single-ended RS-232, and these can be used with differential devices provided they are wired correctly. (Incorrect wiring can cause damage to devices if there are no interfacing circuitry measures in place).

Refer to NMEA 0400 Installation Standard for correct wiring methods.

 NMEA 0183 data is output/input as ‘sentences’, as they use ASCII in their structure. This makes the data ‘human-readable’, and easier to interpret (at least by a human). Whereas NMEA 2000 uses Binary.

 NMEA 2000 was originally designed to replace NMEA 0183 over time, however, this quickly changed, and NMEA 2000 devices now work alongside NMEA 0183 devices thanks to conversion gateways such as the Actisense NGW-1.

NMEA 2000 does not operate on RS-232/422 like 0183, instead, it interfaces all devices together on one network using CAN (Controlled Area Network). NMEA 2000 is based on J1939 high-level protocol but does not use the same messages.

Whilst both 0183 and 2000 share a lot of the same data, their formats are completely different. This means that when it comes to converting between 0183 and 2000 (and vice versa), there is no ‘one to one’ between sentences and 2000 PGNs, and not all PGNs have relevant 0183 conversions.

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