SkyTraq PX1120S - Page 11

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SkyTraq Technology, Inc. Preliminary Draft www.skytraq.com.tw
NMEA Output Description
The output protocol supports NMEA-0183 standard. The implemented messages include GGA, GLL, GSA, GSV, VTG,
RMC, and ZDA messages. The NMEA message output has the following sentence structure:
$aaccc,c–c*hh<CR><LF>
The detail of the sentence structure is explained in Table 1.
Table 1: The NMEA sentence structure
character
HEX
Description
“$”
24
Start of sentence.
Aaccc
Address field. “aa” is the talker identifier. “ccc” identifies the sentence type.
“,”
2C
Field delimiter.
C–c
Data sentence block.
“*”
2A
Checksum delimiter.
Hh
Checksum field.
<CR><LF>
0D0A
Ending of sentence. (carriage return, line feed)
Table 2: Overview of SkyTraq receiver’s NMEA messages
$GPGGA
Time, position, and fix related data of the GPS receiver.
$GNGLL
Position, time and fix status.
$GNGSA
Used to represent the ID’s of satellites which are used for position fix. When GPS satellites are used for
position fix, $GNGSA sentence is output with system ID 1. When GLONASS satellites are used for
position fix, $GNGSA sentence is output with system ID 2. When Galileo satellites are used for position
fix, $GNGSA sentence is output with system ID 3. When BDS satellites are used for position fix,
$GNGSA sentence is output with system ID 4.
$GPGSV
$GLGSV
$GAGSV
$GBGSV
Satellite information about elevation, azimuth and CNR, $GPGSV is used for GPS satellites, while
$GLGSV is used for GLONASS satellites, while $GAGSV is used for GALILEO satellites, while $GBGSV is
used for BEIDOU satellites.
$GNRMC
Time, date, position, course and speed data.
$GNVTG
Course and speed relative to the ground.
$GNZDA
UTC, day, month and year and time zone.