Raymarine NMEA Multiplexer Spezifikationen PDF herunterladen (Seite 22)

When the tablet is connected, it will receive all information from the instruments and the

navigation software calculates the course to steer and drives the autopilot accordingly. Because the

tablet is sending NMEA data, the multiplexer routes this data exclusively to Out 1. The autopilot

will therefore receive information from the tablet only.

When the tablet is not connected or the navigation software is not sending any data, the

multiplexer automatically routes the inputs to Out1, sending the data from the instruments to the

autopilot. This way, the autopilot will receive course information directly from the GPS.

Options

On the Options page several options and conversions can be chosen.

Priority

This option deletes duplicate NMEA sentences received on multiple inputs. When enabled, the

multiplexer assigns a priority to incoming NMEA data based on the input on which it is received.

The USB port and WiFi interface have the highest priority, followed by NMEA In 1, In 2, In 3 and

In 4 in descending order. NMEA conversion results have the same priority as the input that

received the source of the conversion.

If for instance two GPS receivers are connected to input 1 and 2 and both GPS receivers output

GPRMC sentences, only those from the GPS on input 1 are passed. This feature can be useful to set

up a second GPS as a backup for the main GPS.

The multiplexer only uses the Sentence Formatter (the ‘RMC’ part) for comparison - the Talker ID

(the ‘GP’ part) is ignored.

Another useful application of Priority is when a GPS and an AIS transponder are connected to the

multiplexer. An AIS transponder often outputs sentences from its internal GPS. A navigation

program will now receive GPS data from two sources that might differ in position due to GPS

inaccuracy. This will lead to navigation errors. When the AIS transponder is connected to input 1

and the GPS to input 2, all the NMEA sentences from the AIS transponder is passed while duplicate

NMEA sentences (e.g. GPRMC) from the GPS are blocked. When the AIS transponder fails, GPRMC

sentences from the GPS will be passed again after an adjustable timeout.

Note that the priority system does not block an entire input, it only blocks duplicate sentences.

Sentences received from the GPS that are not received on the AIS input are passed.

The following example shows what is passed and what not. The left column in the table shows

sentences from the AIS transponder on input 1 and the right column sentences from the GPS on

input 2. The sentence that is greyed in the table is blocked by the priority system. The table shows

that only the RMC sentence from the GPS is blocked.

The priority feature can store up to 50 different sentence types to determine their priority. A time

out mechanism ensures that sentences received on lower priority inputs are passed again after an

adjustable time out when their duplicates on higher priority inputs are no longer received.

Check GPS status

Normally, the priority system detects the absence of NMEA sentences. With Check GPS status

enabled, it detects invalid sentences, specifically from a GPS.

When a second GPS is connected as a backup to the first GPS, the first

GPS must completely fail (stop sending data) before sentences from

the second GPS are passed. In a situation where the first GPS no

longer receives any signal from satellites (broken antenna, cable etc.),

it will still output NMEA sentences and the priority system will not fall

AIS

(In 1)

GPS

(In 2)

GPRMC

AIVDM

GPGGA

1 2 ... 17 18 19 20 21 22 23 24 25 26 27 ... 43 44

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