CSI Wireless SBX-3, Справочное руководство

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SBX-3 Reference Manual
36
To separate NMEA messages from RTCM data output by Port 0
through a parsing routine, without causing a parity failure of the RTCM,
it is necessary to take advantage of the fact that ‘$’ and ‘<LF>’ are not
supported within the RTCM specification. (provided there are no bit
errors in the RTCM stream to start with). Therefore, if a ‘$’ is received,
then it should be considered as the beginning of a NMEA sentence and
a ‘<LF>’ should be expected within a window of certain length. If the
parsing routine does not receive one, due to an unlikely communication
line error, after a window of a particular number of bits has passed,
resynchronization to the RTCM data must occur.
3.5.2 Dual Serial Port Operation
Although an integration may be designed with a microprocessor
between the SBX-3 and the GPS receiver to tune and monitor SBX-
3status, the second serial port of the SBX-3 eliminates the requirement
to develop a NMEA message parsing algorithm.
With this type of architecture, the SBX-3’s main serial port may be
interfaced to the GPS receiver’s receive line to provide RTCM
correction data. The secondary serial port interfaces to the
microprocessor for NMEA configuration and querying. This ensures
that NMEA response messages do not interrupt the continuous flow of
RTCM data to the GPS receiver.
3.5.3 SBX-3 ‘Y’ Data Cable
The SBX-3 Evaluation Kit comes with a ‘Y’ data cable that terminates at
the receiver end with a single male DB9 plug which branches to two
DB9 sockets at the opposite end. One of the DB9 sockets is labeled
Port 1 for the SBX-3’s primary port and the other Port 2 for the SBX-3’s
secondary port. Both of these two terminations will allow you to plug
directly into a PC computer’s communication port.
The pin-out of this cable is provided in the following table.