GARMIN GPS Interface Specification
GARMIN GPS Interface Specification
GARMIN GPS Interface Specification
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N Direction Packet ID Packet Data Type<br />
0 Device1 → Device2 Pid_Records Records_Type<br />
1 Device1 → Device2 Pid_Almanac_Data <br />
2 Device1 → Device2 Pid_Almanac_Data <br />
… … … …<br />
n-2 Device1 → Device2 Pid_Almanac_Data <br />
n-1 Device1 → Device2 Pid_Xfer_Cmplt Command_Id_Type<br />
The first and last packets (Packet 0 and Packet n-1) are the standard beginning and ending packets (see Section 5.3,<br />
Standard Beginning and Ending Packets, on page 12). The Command_Id_Type value contained in Packet n-1 is<br />
Cmnd_Transfer_Alm, which is also the command value used by the Host to initiate a transfer of the almanac from<br />
the <strong>GPS</strong><br />
Packets 1 through n-2 (Pid_Almanac_Data) each contain almanac data for one satellite, which is provided in<br />
product-specific data type . This data type contains data that describes the satellite’s orbit characteristics.<br />
Some product-specific data types () do not include a satellite ID to relate each data packet to a particular<br />
satellite in the <strong>GPS</strong> constellation. For these data types, Device1 must transmit exactly 32 Pid_Almanac_Data<br />
packets, and these packets must be sent in PRN order (i.e., the first packet contains data for PRN-01 and so on up to<br />
PRN-32). If the data for a particular satellite is missing or if the satellite is non-existent, then the week number for<br />
that satellite must be set to a negative number to indicate that the data is invalid.<br />
Page 26 001-00063-00 Rev. A
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