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E-2 Lassen-SK8 Embedded GPS Module
NMEA 0183
E.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-SK8. 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.
E.3 NMEA 0183 Message Options
The Lassen-SK8 outputs two messages: GGA (NMEA Version 2.1) and VTG. These
messages are output at a 1 second interval with the “GP” talker ID and checksums.
*
Note – The user can configure a custom mix of the messages listed in table C-2. See
TSIP command packet BB in Appendix A for details on configuring NMEA output.