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2.1.3 LED & External Antenna
◆ LED
LED OFF
LED ON
LED Flashing
◆ External Antenna Connector (MCX).....Optional
As using GM-270 CF GPS Receiver in a RV car, truck or bus, it might receive poor
signals through limited view to the sky. Replace the foldable antenna with the active one to
get better satellite signals. Windshields with heavy tinted or likewise may interfere with
signal receiving. An active antenna then becomes essential.
2.2 Software Interface
The GPS-270 interface protocol is based on the National Marine Electronics Association's NMEA 0183 ASCII
interface specification, which is defined in NMEA 0183, Version 2.2 and the Radio Technical Commission for Maritime
Services (RTCM Recommended Standards For Differential Navstar GPS Service, Version 2.1, RTCM Special Committee
No.104).
2.2.1 NMEA Transmitted Messages
The GPS-270PS supported by SiRF Technology Inc. also outputs data in NMEA-0183 format as defined by the
National Marine Electronics Association (NMEA), Standard.
The default communication parameters for NMEA output are 4800 baud, 8 data bits, stop bit, and no parity.
NMEA Record
GGA
GSA
GSV
RMC
•2.2.1.1 Global Positioning System Fix Data (GGA)
Table 2-2 contains the values for the following example:
$GPGGA,161229.487,3723.2475,N,12158.3416,W,1,07,1.0,9.0,M, , , ,0000*18
Name
Message ID
UTC Time
Latitude
N/S Indicator
Longitude
E/W Indicator
Position Fix Indicator
Satellites Used
HDOP
MSL Altitude
Units
Geoid Separation
GM-270 CF GPS Receiver Switch Off.
GM-270 CF GPS Receiver Signal Searching.
GM-270 CF GPS Receiver Signal Position Fixed.
Table 2-1 NMEA-0183 Output Messages
Global positioning system fixed data
GNSS DOP and active satellites
GNSS satellites in view
Recommended minimum specific GNSS data
Table 2-2 GGA Data Format
Example
Units
$GPGGA
161229.487
3723.2475
N
12158.3416
W
1
07
1.0
9.0
Meters
M
Meters
Meters
Description
Description
GGA protocol header
hhmmss.sss
ddmm.mmmm
N=north or S=south
dddmm.mmmm
E=east or W=west
See Table 2-3
Range 0 to 12
Horizontal Dilution of Precision
6
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