How to interpret NMEA 2000 message formats

NMEA 2000 Messages

MEA 2000 data is sent as messages, which we refer to as PGNs. A Parameter Group Number (PGN) is a unique numerical identifier used to categorize and define specific sets of data within the NMEA 2000 protocol. Think about it as a code that groups together related data and enables devices in a network to effectively recognize and interpret information. PGNs define all data sent from a device.

There are 3 types of PGNs:

1. Mandatory:
These PGN types are defined by the NMEA 2000 standard as those that all devices must support.

Mandatory PGN List

2. Common / Data (Common):
These PGN types contain normal data from instruments such as Depth, Position and Temperature.

NMEA 2000 Common PGNs

3. Proprietary:
These PGN types are defined by NMEA to enable the transmission of data outside the approved PGN specification.

An example på this is when manufacturers send specific data to targeted devices for firmware updates or configurations. This is outside the NMEA 2000 standard specification and is of no use to any other manufacturer or connected device, such as; it can be kept as one's own. These messages have the lowest priority in the network and will not take precedence over data or command messages.

There are three conditions that NMEA defines as acceptable usage; the domain for Proprietary PGN:

Own PGN

The serial data used by CAN has a 29-bit identification field and zero to One data byte.

In addition, the frame contains start and end bits, reserved bits, check bits, a 15-bit CRC field for error detection, and acknowledgment bits. 29-bit header, 8-byte data byte, CRC field, end of frame, start på frame, control field, ACK field.

Så Why is this important?

Firstly, these messages and their format are useful for installers and operators when trying to interpret data. Of course, you can't look at dear; binary data and initialization; the, soå we need the PGN content to be decoded. There are several NMEA 2000 PC applications available that do this for you, such as Actisense NMEA Reader.

With NMEA Reader you can see the content of each NMEA 2000 PGN (excluding other manufacturers' own messages) in a readable, decoded format, which Make sure you can interpret the data you receive. This makes basic investigations and troubleshooting exercises possible, because we can now see what data a GPS is sending out, for example, or if it is sending out any data at all.