Garmin GPS 16x 010-00258-62 User Manual

190-00228-08 

GPS 16x Technical Specifications  

Rev. B 

Page 26 

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: 

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: 

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): 

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): 

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