Airmar LB150 - Manual (Page 5)

LB150 WeatherStation Technical Manual revision 0.013
Proprietary and Confidential
PRELIMINARY - DRAFT 2
2. NMEA 0183 Interfaces
The Airmar LB150 WeatherStation has a single standard NMEA 0183-compliant output
channel, and a single standard NMEA 0183-compliant input channel. The unit transmits
standard NMEA 0183 sentences on its output channel. It also recognizes standard and
proprietary NMEA 0183 sentences received on its input channel. The standard baud rate
for both input and output channels is 4800 baud, though if desired this may be increased
to 38400 baud via a proprietary command. 1
The transmitted NMEA 0183 sentences are described in section 2.1. Received NMEA
0183 sentences and proprietary commands are described in section 2.2.
2.1. Transmitted NMEA 0183 Sentences
By default, only certain NMEA sentences are enabled for transmission. Other sentences
may be enabled individually for transmission via commands sent to the input channel. 2
The standard transmission interval for most of the transmitted sentences is once per
second. However, in models that include an integrated GPS, if every sentence were
enabled for transmission, there would not be enough bandwidth in the output channel at
4800 baud to output all sentences within a one second timeframe. Therefore, one or more
of the following remedies should be employed:
• To conserve bandwidth, only enable for transmission those sentences required for
the given application, and disable all others.
• Reduce the frequency of transmission for less critical sentences.
• Increase the overall bandwidth eightfold by increasing the baud rate from the
standard 4800 baud to 38400 baud (though keep in mind that most NMEA 0183
instruments are not capable of operating at 38400 baud)
All NMEA sentences transmitted by the LB150 WeatherStation include a checksum at
the end of the sentence, consisting of an asterisk (*) followed by two ASCII hexadecimal
characters. In the detailed specifications to follow, these hexadecimal characters are
designated by “hh”.
The standard NMEA 0183 sentences provided by the LB150 WeatherStation are
summarized in Table 1. Each of the transmitted sentences in Table 1 is described in
detail on the subsequent pages.
1 See the $PAMTC,BAUD command.
2 See the $PAMTC,EN command.