Fastrax IT321, Техническое описание

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2007-11-19
Page 21 of 35
IT321_Tech_doc_12
4.6.1 Active GPS antenna
The customer may use an external active GPS antenna for e.g. in
mobile or indoor usage. It is suggested the active antenna has a net
gain
including cable loss in the range from +10 dB to +25 dB.
NOTE
Max antenna bias current is 15mA. Antenna
bias circuit has internal short circuit protec-
tion. At short circuit condition the antenna
bias current is limited to abt. 60mA and the
navigation data output will be stopped. Navi-
gation will recover automatically when short
circuit is removed.
4.7 UART
The device supports UART communication via one serial port A.
The default configuration for baud rates and respective protocols can
be changed by commands via NMEA or SiRF binary protocols
(ref II &
III) . Any custom configuration stays active as long as supply VDD is
active.
I/O levels form the serial port is CMOS 1.8V compatible, not RS232
compatible. Use an external level converter to provide CMOS 3.3V or
RS232 levels when needed. The RXA input can be left unconnected
when not needed since it has internal pull up resistor.
4.8 PPS
The pulse-per-second (PPS) output provides a pulse signal for timing
purposes. Pulse length (high state) is about 1us synchronized to full
UTC second. I/O level is CMOS 1.8V compatible.
4.9 ELCK
The ECLK is available optionally for external clock input with special
ROM version for A-GPS frequency aiding. Pull down (e.g. 10kohm) if
not used. I/O level is CMOS 1.8V compatible.