PGN

NMEA2000 Messages are organised into logical collections of data called parameter groups. The NMEA assigns each parameter group a unique Perameter Group number or PGN.

A single frame parameter group has been designed to fit within the 8 bytes of a single CAN frame. NMEA2000 parameter groups are each assigned a priority value between 0 and 7, which is used to arbitrate between two devices which are attempting to transmit simultaneously. 0 is the highest priority and 7 is the lowest.

The priority field at the top of each of the detailed specification pages shows three values separated by slashes (eg. 5/Y/Y). The first value is the defult priority between 0 and 7, of the parameter group detailed in the NMEA2000 standard. The second value is 'Y' if the priority for this parameter group may be changed using the Command Group Function PGN 126208, or 'N' if the priority cannot be changed. The third value is 'Y' if the prioirty is saved in non volatile EEPROM memory within the device and maintained upon cycling power, or 'N' if the priority reverts to the defult value upon cycling power.

NMEA 2000 messages are sent as packets that consist of a header followed by 8 bytes of data. The header for a message specifies the transmitting device, the device to which the message was sent, the message priority, and the PGN. The PGN indicates which message is being sent, and thus how the data bytes should be interpreted to determine the values of the data fields that the message contains.

For more information, please read the 'Terminology' section of the DST200 User Manual.