Furuno NX-300 manual Message Format, Nnnn

1.3 Message Format

For automatic identification of messages, each message starts with eight control characters, called "Header codes".

The first four characters are always "ZCZC" and common to all messages. This part is used for message synchronization. The latter four characters are designated as b1, b2, b3 and b4 to indicate origin, category and serial number of the message.

Character b1 is the identification letter of the NAVTEX station; "A" to "Z". Character b2 indicates the type of message, "A" to "Z", as listed below. Character b3 and b4 indicate the serial number of the message. The serial numbers are counted up from "01" to "99", and start from "01" again. Number "00" is specially reserved for important emergency messages, such as a search and rescue (SAR) message.

The end of each message is indicated by "NNNN" (four successive N's).

General message format is summarized below.

			Header code
		ZCZC b1 b2 b3 b4					main message			NNNN
	Start code						Main message			Termination code
	(sync)				Serial number
				"00":			Emergency message
						"01" - "99": Normal message
					Type of message
						"A" - "Z"
					(See the list below.)
						Station ID
						"A" - "Z"
[Type of message (category)]
A:	Navigational warning							I:	OMEGA message
B:	Meteorological warning							J:	Differential OMEGA message
C:	Ice report							K:	Other electronic navigational aid
D:	Search and rescue information/								system message
	piracy and armed robbery							L:	Navigational warning (additional)
E:	Meteorological forecast							M to U:	Reserve-presently not used
F:	Pilot message							V:	Notice to Fishermen (U. S. only)
G:	DECCA message							W to Y	Reserve-presently not used
H:	LORAN-C message							Z:	QRU (no message on hand)

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