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3.2 Software Interface
This section describes the SV12 GPS Receiver software interface, the start-up
characteristics for the different interface protocols, a description of the receiver operating
modes, and a brief description of the interface protocols.
3.2.1 Start-up
When connected to an external GPS, the SV12 GPS Receiver contains all the circuitry
necessary to automatically acquire GPS satellite signals, track up to 12 GPS satellites,
and compute location, speed, heading, and time. The receiver automatically begins to
search for and track GPS satellite signals at power-up.
The performance of the 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 begins to compute position solutions within the first
two minutes, the receiver must continuously track satellites for approximately 15 minutes
to develop a complete almanac. The 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 responds to commands almost
immediately after power-up.
3.2.2 Communicating with the SV12 GPS Receiver
The SV12 GPS Receiver supports three message protocols: TSIP, TAIP, and NMEA. A
summary of the protocols are discussed below.
Communications with the SV12 GPS Receiver is through two RS-232 serial ports. The
port characteristics can be changed to accommodate your application requirements. Port
parameters are stored in a non-volatile, electrically erasable ROM (EEROM) that does
not require backup power. The following tables list the default characteristics for each
port.
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