Multitech MTCMR-E1 Manual de usuario descargar pdf (Pagina 102)

Chapter 16 – GPS Device AT Commands

102 Universal IP AT Commands Reference Guide

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>

Start of Sequence

All sentences begin with the sentence start delimiter character “$” or “!”.

Address Field

The address field defines the sentence. Characters with digits and upper case letters are allowed in the address

field. 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 “!”.

SUPPORTED MESSAGE LIST

The following NMEA messages are supported.

Sentence

Descriptions

GGA

Global Positioning System Fix Data

GLL

Geographic Position – Latitude/Longitude

GSA

GNSS DOP and Active Satellites

GSV

GNS Satellites in View

RMC

Recommended Minimum Specific GNSS Data

VTG

Course Over Ground and Ground Speed

1 2 ... 97 98 99 100 101 102 103 104 105 106 107 ... 118 119

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