Users manual
Appendix A
Revision #:
A
Date:
07-14-15
Page
6
of
58
3
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>
