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190-00879-08 GPS 18x Technical Specifications Rev. D
Page 26
The satellite data has a record ID of 0x72 with 84 (0x54) data bytes. The data bytes contain data for 12 satellites as
described below.
Satellite Data Record
typedef struct
{
uint8 svid; //space vehicle identification (1–32 and 33–64 for WAAS)
uint16 snr; //signal-to-noise ratio
uint8 elev; //satellite elevation in degrees
uint16 azmth; //satellite azimuth in degrees
uint8 status; //status bit-field
} cpo_sat_data;
The status bit field represents a set of booleans described below:
Bit Meaning when bit is one (1)
0 The unit has ephemeris data for the specified satellite.
1 The unit has a differential correction for the specified satellite.
2 The unit is using this satellite in the solution.
This pattern is repeated for 12 satellites for a total of 12 X 7 bytes = 84 (0x54) bytes.
The RS-232 Packet for the Satellite Record looks like:
- 0x10 (DLE is first byte)
- 0x72 (Record ID – single byte)
- 0x54 (Number of data bytes – single byte)
- 12 cpo_sat_data records
- 0x## (2’s complement of the arithmetic sum of the bytes between the delimiters)
- 0x10 (DLE)
- 0x03 (ETX is last byte)
The USB Packet for the Satellite Record looks like:
- 0x14 0x00 0x00 0x00 (USB Transport ID, 1 byte unsigned, 4 bytes reserved)
- 0x72 0x00 0x00 0x00 (Record ID, 2 bytes unsigned, 4 bytes reserved)
- 0x54 0x00 0x00 0x00 (Number of data bytes, 4 bytes unsigned)
- 12 cpo_sat_data records