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Lassen-SK8 Embedded GPS Module A-45
Trimble Standard Interface Protocol
A.17.40 Report Packet 0x5A
This packet provides raw GPS measurement data. If the I/O “auxiliary” option has been
selected, the receiver sends this data automatically as measurements are taken. The data
format is shown below.
Note – A new Report Packet, 0x 6F has full pseudo-ranges and integrated doppler.
Application Note – Packet 0x5A provides the raw satellite signal measurement
information used in computing a fix.
Satellite PRN (Byte 0) is a unique identification number or each of the 32 GPS satellites.
Sample length (Byte 1) is the number of milliseconds over which the measurement was
averaged. thus if the sample length is 428, then the receiver tracked the satellite and
collected the measurement over a 428 millisecond period. The receiver uses a 500
millisecond dwell time per satellite, however, if the channel is sequencing on several
satellites, the sample length will be closer to 400 milliseconds due to re-acquisition and
loop setting times.
The codephase (Byte 9) value is the average delay over the sample interval of the received
C/A code and is measured with respect to the receiver's millisecond timing reference.
Thus, it includes all receiver, satellite, and propagation biases and errors. It is expressed in
1/16th of a C/A code chip.
The doppler (Byte 13) value is apparent carrier frequency offset averaged over the sample
interval. It is measured with respect to the nominal GPS L1 frequency of 1575.42 MHz,
referenced to the receiver's internal oscillator. Thus, it includes all receiver and satellite
clock frequency errors. It is expressed in Hertz at the L1 carrier.
The time of measurement (Byte 17) is the center of the sample interval adjusted by adding
the receiver supplied codephase (modulo mS) to a user determined integer number of mS
between user and satellite.
Table A-48. Report Packet 0x5A Data Formats
Byte Item Type Units
0 Satellite PRN Number BYTE -----
1 Sample Length SINGLE msec
5 Signal Level SINGLE AMU or dBHz
9 Code phase SINGLE 1/16th chip
13 Doppler SINGLE Hertz
17 Time of Measurement DOUBLE sec