Installation Manual

AIS Installation Manual Issue 1 41
8 Serial interface communications protocols
The Transponder has eight RS-422 interfaces:
• 4 sensor data input ports SEN1, SEN2, SEN3 and SEN4
• 2 Bi-directional input/output ports MAIN and AUX/Pilot
• 1 Bi-directional input/output port RTCM
• 1 Bi-directional input/output port Long Range
8.1 Sensor data interface
The Sensor data input ports receive navigational data in NMEA–0183 format from the
connected sensors. The connected sensors can be a GNSS unit used for navigation, a
gyrocompass and a bottom track log. These data are processed in the AIS unit and transmitted
as dynamic data. The data received by other stations over the VHF link form an image of the
sensor data. It is therefore vital that the sensor data are correct and that the port is correctly
configured.
Navigational data must be received via the sensor ports within certain intervals; the maximum
intervals are listed in the table below. If NMEA sentences containing identical information arrive
at the sensor input ports, the AIS Transponder will choose the information with the highest
priority level.
The built-in GNSS unit will under normal conditions only be used for TDMA slot timing. However
if no data are received from the external sensors, the built-in GNSS unit can be set to take over
automatically and supply navigational information for the VHF data link transmission. The
changeover between internal GNSS information and external sensor information happens
automatically. Information received from the external sensors has priority and will always be
used when available.
Messages received and interpreted from sensors:
Data type Max update
interval [s]
NMEA application Default parameter value
Date 3 RMC Year 2000, month. 0, day 0
UTC 3 GNS, RMC, GGA,
GLL
24:60:60
Lat, Lon 3 GNS, RMC, GGA,
GLL
91°00′00″ nl, 181°00′00″ wl
Datum 30 DTM Not defined
SOG,
COG
3 RMC, VBW 102.3, 360°
Altitude 3 GNS 4095
Heading 10 HDT 511
Turn rate 10 ROT -128
RAIM 10 GBS Ok
Route plans with positions are transmitted in RTE (Routes) and WPL (Waypoint location)
sentences. There is no update interval for these data, therefore the last updated Route plan will
be kept in memory until data are updated or the power is switched off, as the data are not kept
in the permanent memory.
8.2 Main and AUX port reception and transmission of AIS data
Specific AIS Transponder functions are available via the Main and AUX ports. The ports are
identical and will transmit all received VDL (VHF Data Link) messages as well as Transponder