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190-00266-01 GPS 15H & 15L Technical Specifications Rev. D
Page 33
Each data member of the ephemeris data structure is indexed into the data array of the ephemeris packet
and cast as the appropriate data type. The indices are as follows (note that they correlate to the data
members of the structure respectively):
#define IDX_EPH_WN 0
#define IDX_EPH_TOC 4
#define IDX_EPH_TOE 8
#define IDX_EPH_AF0 12
#define IDX_EPH_AF1 16
#define IDX_EPH_AF2 20
#define IDX_EPH_URA 24
#define IDX_EPH_E 28
#define IDX_EPH_SQRTA 36
#define IDX_EPH_DN 44
#define IDX_EPH_M0 52
#define IDX_EPH_W 60
#define IDX_EPH_OMG0 68
#define IDX_EPH_I0 76
#define IDX_EPH_ODOT 84
#define IDX_EPH_IDOT 88
#define IDX_EPH_CUS 92
#define IDX_EPH_CUC 96
#define IDX_EPH_CIS 100
#define IDX_EPH_CIC 104
#define IDX_EPH_CRS 108
#define IDX_EPH_CRC 112
#define IDX_EPH_IOD 116
The last packet is a “download complete” packet that looks like this:
TX Packet: Download Complete
Byte Description Name HEX Value
Delimiter DLE 0x10
Download Complete ID IOP_DL_CMPLT 0x0c
Number of bytes in data SIZE 0x02
Ephemeris Download ID IOP_DOWN_LOAD_EPH 0x5D
Pad DATA 0x00
Checksum calculation CHKSUM ----
Delimiter DLE 0x10
End of packet ETX 0x03
After properly acknowledging this packet (ACK the IOP_DL_CMPLT ID), the ephemeris download is
complete.