Nmea Sentence Structure - Simrad ES80 Reference Manual

Electronic Devices document explains the formats in detail. The document can be
obtained from NMEA.
Note
The terms "Datagram" and "telegram" are generally used to describe the basic transfer
unit associated with a packet-switched network. In this publication, we use the term
"datagram".

NMEA sentence structure

A sentence structure is defined by NMEA to establish the communication between two
units. Most other datagram formats are designed using the same, or a similar, structure.
The following provides a summary explanation of the approved parametric sentence
structure:
$aaccc,c-c*hh<CR><LF>
1
$
This character (Hex: 24) is used to identify the start of a sentence.
2
aaccc
This is the address field. The first two characters (aa) identify the talker ID, while
the last three characters are the sentence formatter mnemonic code identifying the
data type and the string format of the successive fields.
3
,
The comma (Hex: 2C) is used as a field delimiter. This character starts each field
except the address and checksum fields. If it is followed by a null field, it is all that
remains to indicate that there are no data in the field.
4
c-c
This is the data sentence block. This is a series of data fields containing all the data
to be transmitted. The data field sentence is fixed and identified by the sentence
formatter in the address field. Data fields may be of variable length, and they are
preceded by the field delimiter.
5
*
This character (Hex: 2A) is the checksum delimiter. This delimiter follows the last
field of the sentence and indicates that the following two alphanumerical characters
contain the checksum.
6 hh
This is the checksum.
7
<CR><LF>
The carriage return and line feed characters terminate the sentence.
406273/C
Datagram formats
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