Garmin 16" x Ephemeris Download Procedure, Name, Name, Name, Name, HEX Value, HEX Value, HEX Value, HEX Value, Byte Description, Byte Description, Byte Description

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
190-00228-08	GPS 16x Technical Specifications	Rev. A
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