Multi-Tech Systems iCell GPRS (MTSMC-G2-IP Manual Do Utilizador

Part 6 – AT Commands for GPS-Enabled Devices

Chapter 16 – AT Commands for GPS-Enabled Devices

Universal IP AT Commands Reference Guide (Document S000457K)

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 !

[,<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 “!”.