Airmar LB150 - Manual (Page 32)

LB150 WeatherStation Technical Manual revision 0.013
Proprietary and Confidential
PRELIMINARY - DRAFT 29
2.2. Received NMEA 0183 Sentences and Commands
The LB150 WeatherStation has an NMEA 0183-compliant input channel that is capable
of receiving standard NMEA sentences as well as proprietary commands for
initialization, calibration, or to modify the behavior of the unit.
All received sentences and commands can include or omit the NMEA checksum. If a
checksum is included, the sentence will be checked against its checksum, and the
sentence will be accepted only if there is a checksum match. If the NMEA checksum is
excluded, it is required that the preceding asterisk (*) also be excluded. If no checksum
is provided, the LB150 WeatherStation will accept the sentence without error checking.
It is recommended that all sentences and commands provided to the WeatherStation
include a checksum to help ensure integrity of the transmitted data.
The sentences recognized by the LB150 WeatherStation on the serial input channel are
summarized in Table 2 on the next page.
Note that the prefix “$--” appearing in the descriptions for several of the listed
sentences should be replaced by a “$” followed by the two-character talker ID of the
transmitting device.
Each of the sentences in Table 2 is described in detail on the subsequent pages.
2.2.1. Precedence of Data
In a given installation, certain data items might be available from more than one source.
In this circumstance, the following precedence rules apply. The calculation of true wind,
in particular, depends on these precedence rules.
Heading and Deviation:
$--HDT supersedes $--HDG and the internal compass.
$--HDG supersedes the internal compass
$--VHW (Note: if heading is supplied in this received sentence, it is ignored.)