Garmin 15 H Series, Technical Specifications

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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 Name HEX Value
Delimiter DLE 0x10
Command Data ID IOP_CMND_DATA 0x0A
Number of bytes in data SIZE 0x02
Request to D/L ephemeris IOP_DOWN_LOAD_EPH 0x5D
Pad to 2 bytes DATA 0x00
Checksum calculation CHKSUM 0x97*
Delimiter DLE 0x10
End ETX 0x03
* 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 Name HEX Value
Delimiter DLE 0x10
Acknowledgement ID IOP_ACK_BYTE 0x06
Number of bytes in data SIZE 0x02
Request to D/L ephemeris IOP_CMND_DATA 0x0A
Pad DATA 0x00
Checksum calculation CHKSUM ----
Delimiter DLE 0x10
End of packet ETX 0x03
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 Name HEX Value
Delimiter DLE 0x10
Record ID IOP_RECORDS 0x1B
Number of bytes in data SIZE 0x02
Number of records NUM_SV 0x0C
Pad DATA 0x00
Checksum calculation CHKSUM ----
Delimiter DLE 0x10
End of packet ETX 0x03
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 Name HEX Value
Delimiter DLE 0x10
Record ID IOP_ACK_BYTE 0x06
Number of bytes in data SIZE 0x02
Pad DATA 0x00
ID of packet being ACK’d IOP_RECORDS 0x1B
Checksum calculation CHKSUM ----
Delimiter DLE 0x10
End of packet ETX 0x03