7
$PNMRX603
Settings Report
Out
General NMEA Format
The general NMEA format consists of an ASCII string commencing with a ‘$’ character and
terminating with a <CR><LF>
sequence.
NMEA standard messages commence with ‘GP’ then a
3-letter message identifier. NemeriX specific messages commence
with $PNMRX followed by a 3
digit number.
The message header is followed by a comma delimited list of fields optionally
terminated with a checksum consisting of an asterix ‘*’ and a 2 digit hex value representing the
checksum. There is no comma preceding the checksum field. When present, the checksum is
calculated as a bytewise exclusive of the characters between the ‘$’ and ‘*’. As an ASCII
representation, the number of digits in each number will vary depending on the number and
precision, hence the record length will vary. Certain fields may be omitted if they are not used, in
which case the field position is reserved using commas to ensure correct interpretation of
subsequent fields.
The tables below indicate the maximum and minimum widths of the fields to allow for buffer
size allocation.
$GPGGA
This message transfers global positioning system fix data. The $GPGGA message structure is
shown below:
Field
Format
Min chars
Max chars
Notes
Message ID
$GPGGA
6
6
GGA protocol header.
UTC Time
hhmmss.sss
2,2,2.3
2,2,2.3
Fix time to 1ms accuracy.
Latitude
float
3,2.4
3,2.4
Degrees * 100 + minutes.
N/S Indicator
char
1
1
N=north or S=south
Longitude
float
3,2.4
3,2.4
Degree * 100 + minutes.
E/W
indicator
Char
1
1
E=east or W=west
Position Fix
Indictor
Int
1
1
0: Fix not available or invalid.
1: GPS SPS mode. Fix available.
Satellites
Used
Int
2
2
Number of satellites used to calculate fix.
HDOP
Float
1.1
3.1
Horizontal Dilution of Precision.
MSL Altitude
Float
1.1
5.1
Altitude above mean seal level
Units
Char
1
1
M Stands for “meters”.
