21NMEA-NX2.doc Page 2 Latest update: 27 Jan -03
21.2 NMEA Output
The NMEA output is utilising the industry standard RS-422. The two wires (yellow
and white) are named A and B.
The signal difference between A and B is allowed to be between 3V and 12V.
B has a signal that is always inverted to A => A=B
The advantages of the RS-422 is that it is insensitive for disturbances.:
If the signals gets disturbed, both of the signal levels (A+B) are disturbed
proportionally i.e. A=33V => B=30V => A-B = 3V
A=3003V => B=3000V => A-B=3V
The Server-Unit is the main NMEA output source for the NEXUS Network. It's the
only unit that can send all types of data from the NEXUS Network.
The output is divided into 16 different "time-slots". The wanted NMEA sentence
can be selected (or deactivated) individually for each slot. The complete period
for all slots are 2 seconds, so the time between each slot is 0.125 sec.
All data that is not available will be sent with null fields.
Checksum is added only where it is mandatory. Talker ID (address character 1
and 2) is always II (Integrated Instrumentation).
The following sentences can be selected (from MULTI Instrument: Remote
Control or Multi Center):
The NX2 Server sends NMEA-sentences continuously. The following, C77 to C92
per below, is transmitted in default setting of the NX2 Server (see also User
Manual 3.11.1)
0 (- - -) No out signal
1 (APB) Autopilot B
2 (BOD) Bearing original destination
3 (BWC) Bearing and distance to waypoint
4 (BWR) Bearing and distance, dead reckoning
5 (C77) (DBT) Depth measured from the transducers position
6 (DPT) Depth
7 (C78) (GLL) Geographic position
8 (GSA) DOP and active satellites
9 (C79) (GSV) Satellites in view
10 (C80) (HDM) Magnetic heading
11 (C81,89) (HDT) True heading
Transmitting
MPU
RS -422
OUT
OUT
RETURN
Write
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