SECTION 4
SOFTWARE INTERFACE
The GPS 35/36 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 35/36 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 35/36. The
baud rate selection and RTCM differential GPS input are
also described.
4.1 NMEA RECEIVED SENTENCES
The subsequent paragraphs define the sentences which
can be received on RXD1 by the GPS 35/36. These
sentences are echoed upon receipt to provide handshaking
that the appropriate information was received by the GPS
35/36.
hh = 1 byte checksum
4.1.1 Almanac Information (ALM)
$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
17
