Lassen SQ, Reference Manual

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3 Software Interface
3 4 Lassen SQ GPS Receiver
3.1
Start-up
Lassen SQ GPS module is a complete 8-channel parallel tracking GPS
receiver designed to operate with the L1 frequency, standard position
service, Coarse Acquisition code. When connected to an external GPS
antenna, the receiver contains all the circuitry necessary to
automatically acquire GPS satellite signals, track up to 8 GPS
satellites, and compute location, speed, heading, and time. The
receiver will automatically begin to search for and track GPS satellite
signals at power-up.
The performance of a GPS receiver at power-on is determined largely
by the availability and accuracy of the satellite ephemeris data and the
availability of a GPS system almanac.
The first time the receiver is powered-up, it is searching for satellites
from a cold start (no almanac). While the receiver will begin to
compute position solutions within the first two minutes, the receiver
must continuously track satellites for approximately 15 minutes to
download a complete almanac. This initialization process should not
be interrupted. With a complete almanac and back-up power, the time
to first fix can typically be shortened to less than 45 seconds. The
receiver will respond to commands almost immediately after power-up
(see Warning below).
Note – See Chapter 4 for further detail on ephemeris data and the
GPS almanac.
Warning – The Lassen SQ GPS receiver is ready to accept TSIP
commands approximately 2.1 seconds after power -up. If a command is
sent to the receiver within this 2.1 second window, the receiver will ignore
the command. The Lassen SQ GPS receiver will not respond to
commands sent within the 2.1 second window and will discard any
associated command data.