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Part 6 – AT Commands for GPS-Enabled Devices Chapter 16 – AT Commands for GPS-Enabled Devices
Universal IP AT Commands Reference Guide (Document S000457K) 98
Application Note – GPS NMEA Messages
Introduction
The NMEA (National Marine Electronics Association) 0183 Standard is a standard protocol for
interfacing navigational devices; e.g., GPS and DGPS receivers over a serial interface. The
complete document of this standard may be obtained from NMEA at
http://www.nmea.org. We
wish to thank SkyTraq Technology, Inc. for providing the following summary of NMEA Messages.
NMEA Protocol Overview
Message Format
The structure of an NMEA message is shown below.
Checksum Range
Start of
Sequence
Address Field
Data Field(s)
Checksum
Field
End of
Sequence
$ or !
<Address>
[,<data field>] [,<data field>]
*<checksum>
<CR><LF>
Start of Sequence
All sentences begin with the sentence start delimiter character “$” or “!”.
Address Field
The address field is used to define the sentence. Characters with digits and upper case letters
are permitted to be in the address field. Note that the address field is required. It cannot be a null
field. This field is subdivided into 2 fields.
<XX>
<XXX>
Talker Identifier
Sentence Formatter
Talker Identifier is always GP for a GPS receiver. The sentence formatter defines the format and
the type of data.
Data Field(s)
Data fields are delimited by a “,” and contain valid characters specified in NMEA 0183 standard. It
can consist of fields of variable lengths.
Checksum
The checksum field is the 8-bit exclusive OR (no start or stop bits) of all characters in the
sentence. Checksum consists of 2 characters and is represented as a hex number.
End of Sequence
All sentences always end with sentence termination delimiter character “$” or “!”.