Users manual
N4430-O-G
Revision #:
B
Date:
8-23-18
Page
18
of
74
NMEA Sentence Format
13.1
Standard Sentence
Format:
5 bytes
Field
Description
$
Start-of Sentence marker
<address field>
5-byte fixed length. First 2 bytes represent a talker ID, and the
remaining 3 bytes do a sentence formatter.
All output sentences must begin with a “$” followed by a
TalkerID.
The relevant Talker IDs are GP for GPS, GN for GNSS, GL for
GLONASS and GA for Galileo.
For the sentences received from external equipment, the GT-87
accepts any talker ID. Talker ID
“XX”
found on the succeeding pages
is a wildcard meaning “any valid talker
ID”.
<data field>
Variable or fixed-length fields preceded by delimiter
“,”(comma).
Comma(s) are required even when valid field data are not available
i.e. null fields. Ex.
“,,,,,”
In a numeric field with fixed field length, fill unused leading digits
with zeroes.
*<checksum field>
8 bits data between “$” and “*” (excluding “$” and “*”) are
XORed,
and the resultant value is converted to 2bytes of hexadecimal
letters. Note that two hexadecimal letters must be preceded by
“*”,
and delimiter “,” is not
required before *<checksum>.
All output sentences have checksum.
For input sentences, the resultant value is checked and if it is not
correct, the sentence is treated invalid.
<CR><LF>
End-of-Sentence marker
$
<address field>
,
<data field>
…
*<checksum field> <CR> <LF>
