User Manual

GM862-GPS Software User Guide

1vv0300729 Rev. 5 - 05/07/07

5 GPS operations

5.1 Introduction

The GM862-GPS module is equipped with a SiRFStar III GPS receiver that is controllable by the GSM

modem using a setof AT commands or dedicated NMEA sentences.

5.2 GM862-GPS Serial Ports

2 serial ports are available on the module:

• MODEM SERIAL PORT

• GPS SERIAL PORT B (NMEA)

5.2.1 GPS SERIAL PORT B (NMEA)

This port is carrying out the GPS navigation data in NMEA 0183 format.

The default configuration is 4800 bps, 8, n, 1

It is available on the following pins:

PIN # NAME DESCRIPTION TYPE

35 TX_GPS GPS TX Data (NMEA) CMOS 2.8V

41 RX_GPS GPS RX Data (NMEA) CMOS 2.8V

5.3 WGS 84

GPS receivers perform initial position and velocity calculations using an earth-centered earth-fixed

(ECEF) coordinate system. Results may be converted to an earth model (geoid) defined by the

selected datum. For GM862-GPS the default datum is WGS 84 (World Geodetic System 1984) which

provides a worldwide common grid system that may be translated into local coordinate systems or

map datums. (Local map datums are a best fit to the local shape of the earth and not valid worldwide).