User manual

NMEA Data Multiplexer - NDC-4-A & NDC-4-A -USB
Page 31© 2009 Active Research Limited
The NDC-4-ASW Autoswitch
The Actisense NMEA Data Multiplexer / Combiner /
Autoswitch (NDC-4) 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 data1.
An invalid NMEA sentence checksum2.
If the validity ag(s) contained within the received 3.
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 Actisense
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
the NDC 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 NDC Control Centre.
In the ‘Port Congure’ tab click on the button labelled
“Change To Autoswitch” to change the NDC-4’s operation
mode to Autoswitch.
Figure 22 – “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.