157
Commands
$PASHQ,GSN,[c1]
This command allows you to query for the GSN message, where c1 is the optional
port designator for the output of the response. If a port is not specified, the receiver
sends the response to the current port.
$GPGSN
This message is not output until the receiver has locked on at least one satellite.
The first data field in the GSN message contains the number of satellites currently
being used to compute positions, followed by two fields containing a satellite PRN
number and the measured (dbHz) signal-to-noise ratio for that satellite. The last
field before the checksum contains the age of correction for differential GPS.
Generally speaking, the receiver will be able to lock more quickly, and will be better
able to maintain lock, on satellites whose signals register higher signal-to-noise
values. The response is output in the format:
$GPGSN,d1,((d2,d3)*d1),d4*hh
The fields containing the PRN number (d2) and the signal-to-noise ratio (d3) are
repeated for each locked satellite, with the d1 value used as a multiplier.
Typical GSN message:
$GPGSN,07,01,048,29,046,25,048,08,040,31,037,15,048,21,046, 999*4F
Table 4.83 describes the typical GSN response message.
Table 4.82. $GPGSN Message Format
Parameter Description Range
d1 Number of satellites currently locked 0 - 12
d2 Satellite PRN number 01 - 32
d3 Signal to noise ratio for the corresponding satellite 000 - 999
d4 Age of differential correction. The number 999 is registered in
this field when the G12 is set in differential rover mode but is
not receiving corrections or when differential GPS is disabled.
1 - 999
*hh Checksum 2-character hex
Table 4.83. Typical GSN Message
Field Description
$GPGSN Header
07 Number of satellites currently locked
01 PRN number of the first satellite
G12RevD.book Page 157 Tuesday, April 2, 2002 4:33 PM
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