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SECTION 4
SOFTWARE INTERFACE
The GPS 30/30 SL interface protocol design is based on
the National Marine Electronics Association’s NMEA 0183
ASCII interface specification, which is fully defined in
“NMEA 0183, Version 2.0” (copies may be obtained from
NMEA, P.O. Box 50040, Mobile, AL, 36605, U.S.A.) and
the Radio Technical Commission for Maritime Services’
“RTCM Recommended Standards For Differential Navstar
GPS Service, Version 2.0, RTCM Special Committee No.
104” (copies may be obtained from RTCM, P.O. Box
19087, Washington, D.C., 20036, U.S.A.). The GPS 30/30
SL interface protocol, in addition to transmitting navigation
information as defined by NMEA 0183, transmits additional
information using the convention of GARMIN proprietary
sentences.
The following sections describe the data format of each
sentence transmitted and received by the GPS 30/30 SL.
The baud rate selection and RTCM differential GPS input
are also described.
4.1NMEA RECEIVED SENTENCES
The subsequent paragraphs define the sentences which
can be received on RXD1 by the GPS 30/30 SL. These
sentences are echoed upon receipt to provide handshaking
that the appropriate information was received by the GPS
30/30 SL.
4.1.1 Almanac Information (ALM) (GPS 30 Rev. 1.30
or later and all GPS 30 SLs)
$GPALM,<1>,<2>,<3>,<4>,<5>,<6>,<7>,<8>,<9>,<10>,<11>,<12>,<
13>,<14>,<15>*hh<CR><LF>
The $GPALM sentence can be used to initialize the sensor
board's stored almanac information if battery back-up has
failed.
