DR + GPS
STARTER KIT REFERENCE MANUAL
Lassen DR + GPS Reference Manual 36
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 DR GPS. 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.
Null field, (no characters between commas), indicate data is not currently
available.
Future versions of these messages may have extra fields added to the end.