Ephemeris Download Procedure
The following is the sequence of events that occurs when downloading ephemeris.
Send a packet containing the command that requests ephemeris data (IOP_DOWN_LOAD_EPH). The
packet should look like this:
TX Packet: Ephemeris Data Request
Byte Description
Delimiter
Command Data ID
Number of bytes in data
Request to D/L ephemeris
Pad to 2 bytes
Checksum calculation
Delimiter
End
* From now on, checksum calculation will not be shown for every packet example
The unit will return an acknowledgement packet that will look like this:
RX Packet: Acknowledgement
Byte Description
Delimiter
Acknowledgement ID
Number of bytes in data
Request to D/L ephemeris
Pad
Checksum calculation
Delimiter
End of packet
Then, the unit will immediately send a packet communicating how many data packets to expect for the
ephemeris download (a maximum of twelve):
RX Packet: Number of Data Packets to Expect
Byte Description
Delimiter
Record ID
Number of bytes in data
Number of records
Pad
Checksum calculation
Delimiter
End of packet
This packet requires acknowledgement, as shown below (note that the data field contains the
IOP_RECORDS ID to indicate the acknowledgement of the IOP_RECORDS packet):
TX Packet: Acknowledgement
Byte Description
Delimiter
Record ID
Number of bytes in data
Pad
ID of packet being ACK'd
Checksum calculation
Delimiter
End of packet
190-00228-20
Name
DLE
IOP_CMND_DATA
SIZE
IOP_DOWN_LOAD_EPH
DATA
CHKSUM
DLE
ETX
Name
DLE
IOP_ACK_BYTE
SIZE
IOP_CMND_DATA
DATA
CHKSUM
DLE
ETX
Name
DLE
IOP_RECORDS
SIZE
NUM_SV
DATA
CHKSUM
DLE
ETX
Name
DLE
IOP_ACK_BYTE
SIZE
DATA
IOP_RECORDS
CHKSUM
DLE
ETX
GPS 16/17 Technical Specifications
Page 30
HEX Value
0x10
0x0A
0x02
0x5D
0x00
0x97*
0x10
0x03
HEX Value
0x10
0x06
0x02
0x0A
0x00
----
0x10
0x03
HEX Value
0x10
0x1B
0x02
0x0C
0x00
----
0x10
0x03
HEX Value
0x10
0x06
0x02
0x00
0x1B
----
0x10
0x03
Rev. C
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