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Trimble ThunderBolt E GPS Disciplined Clock User Guide 19
Setting up and Running the ThunderBolt E 2
If the host has not uploaded a reference position, or if the module has been moved
more than one to two kilometers since its last position, the GPS module automatically
conducts a position survey at startup. By default, the GPS module averages 2000
position fixes before entering the clock-only mode. The host system can adjust the
survey period using packet 0x8E-A6. While the GPS module is performing its survey,
the accuracy of the timing outputs will be degraded.
Uploading a reference position
To upload an accurate reference position, use packet 0x31 (Command Packet 0x31:
Accurate Initial Position (XYZ Cartesian ECEF), page 44), or packet 0x32 (Command
Packet 0x32: Accurate Initial Position (Latitude, Longitude, Altitude), page 44): The
reference position is stored in EEPROM (Electrically Erasable Programmable Read-
Only Memory) and is retained during power loss. When a reference position is stored
in EEPROM, the GPS module bypasses the position survey procedure and enters
clock-only mode. If you move the antenna, you must send packet 0x8E-45 to clear the
position stored in EEPROM: The GPS module then initiates a self-survey, unless the
host uploads a new position using packet 0x31 or packet 0x32.
To store the reference position from the self-survey procedure in the EEPROM, send
packet 0x8E-4C to the receiver. Alternatively, you can configure the ThunderBolt E to
automatically save the position using packet 0x8E-A9.