Lassen SQ, Reference Manual

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Lassen SQ GPS Receiver 1 3 9
NMEA 0183 C
C.2
NMEA 0183 Message Format
The NMEA 0183 protocol covers a broad array of navigation data.
This broad array of information is separated into discrete messages
which convey a specific set of information. The entire protocol
encompasses over 50 messages, but only a sub-set of these messages
apply to a GPS receiver like the Lassen SQ GPS receiver. The NMEA
message structure is described below.
$IDMSG,D1,D2,D3,D4,.......,Dn*CS[CR][LF]
“$” The “$” signifies the start of a message.
ID The talker identification is a two letter mnemonic
which describes the source of the navigation
information. The GP identification signifies a GPS
source.
MSG The message identification is a three letter mnemonic
which describes the message content and the number
and order of the data fields.
“,” Commas serve as delimiters for the data fields.
Dn Each message contains multiple data fields (Dn)
which are delimited by commas.
“*” The asterisk serves as a checksum delimiter.
CS The checksum field contains two ASCII characters
which indicate the hexadecimal value of the
checksum.
[CR][LF] The carriage return [CR] and line feed [LF]
combination terminate the message.
NMEA 0183 messages vary in length, but each message is limited to
79 characters or less. This length limitation excludes the “$” and the
[CR][LF]. The data field block, including delimiters, is limited to 74
characters or less.