Actisense NMEA 0183 User Manual download pdf (Page 17)

NMEA Data Multiplexer - NDC-4

The NDC-4-ASW Autoswitch

The Actisense NMEA Data Multiplexer / Combiner /

Autoswitch (NDC) has been designed with the ability to

operateasaMultiplexer/CombinerORanAutoswitch.

For systems that have multiple NMEA devices of an

identical type (e.g. two GPS’s or two depth sounders),

automatic selection of the highest priority device is

normally a vital requirement. However, the NMEA 0183

standard has no method of automatically switching

between differentdevices, so this requirement is usually

fullledwithamanualchangeoverswitch:notaverygood

solution,buttheonlyoneavailableuntilnow.

If the NMEA data from two (or more) devices are simply

combinedtogether,theNMEAlistener(s)willnotbeableto

differentiatebetweenthevarioussourcesandwillgetvery

confused, often jumping between them.If this creates a

‘jumping’positionx,vesselsafetyisseriouslyaffected.

The NDC-4 Autoswitch mode is the perfect solution to this

problem-automaticallyselectingasingledevicefromthe

multiple‘samedatatype’devicesavailable.

Autoswitch mode will automatically select the highest

priority device from up to 4 connected input devices, with

NMEA port 1 as the highest priority through to NMEA port

4 as the lowest. This creates a system capable of

automatically selecting the next priority device if the higher

priority device fails for one of three reasons:

• A complete failure to send any NMEA data.

• An invalid NMEA sentence checksum.

• Ifthevalidityag(s)containedwithinthereceivedNMEA

sentence indicate that this data is not valid and should

onlybeusedwithcaution.

With the addition of two fully Baud rate congurable

outputsprotectedbyISO-Drivetechnology,thatcanalso

incorporate NMEA ltering to remove any unwanted

sentences before the switching process, the NDC-4

Autoswitchmodeisthemostexibleavailable.

Having the ability to lter out NMEA data before the

autoswitch process can be particularly useful to avoid

unwanted sentences from causing the Autoswitch to

change input channels due to invalid data, leaving only the

required sentences to switch on.

If ordered as an Autoswitch, the NDC-4 will be pre-

conguredasanNDC-4-ASWandbereadytoworkoutof

thebox.Alternatively,anyNDC-4canbeconguredusing

Control Centre to operate in Autoswitch mode.

Setting the NDC-4 as an Autoswitch

TheNDC-4caneasilybechangedbetweenbeingaNMEA

Data Multiplexer / Combiner and an NMEA Autoswitch

using Control Centre.

In the ‘Port Congure’ tab click on the button labelled

“Change ToAutoswitch” to change the NDC’s operation

mode to Autoswitch.

Figure 12 – “Change To/From Autoswitch” message

Awarningmessagewillbedisplayed,requestingthatthe

userconrmtherequestto change toAutoswitchmode.

Selecting ‘Yes’ will automatically send the new

congurationtotheunit,andtheNDC-4willnowAutoswitch

itsinputsinsteadofCombiningthem.

To revert back to Combiner mode, click on the (same)

button(nowlabelled‘Change To Combiner’). Again, the

usermustconrmtheoperatingmodechangeisrequired

and the NDC-4 will now Combine its inputs instead of

Autoswitching them. There is no need to click the ‘Send to

Hardware’button,thiscongurationchangeisautomatic.

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Actisense NMEA 0183 User Manual Page 17

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