User manual

NMEA Data Multiplexer - NDC-4-A & NDC-4-A -USB
Page 23© 2009 Active Research Limited
Inclusion List conguration tab
The Inclusion List conguration tab of the main window allows the user to select which NMEA sentences are to be
included in the onward data transmission from the NMEA Data Combiner. Each of the four NMEA input ports and the
USB input port have their own Inclusion List, so that each can be tuned separately to match its connected device.
Figure 13 – Inclusion List conguration tab
Why is there a need for Inclusion Lists?
Each of the 5 input ports can transfer anything up to 480
bytes of data per second, making a total of 1920 bytes/
second. The data combined output of the NDC is also
forced (by the NMEA 0183 standard) to send a maximum
of 480 bytes/second. Therefore, there exists the distinct
possibility that there could be more data to send out than
is possible to achieve - thus, some data may require
removal to balance this equation. The Actisense™ NDC-
4 achieves this reduction in an intelligent manner with
Inclusion Lists and Port Priorities.
Is some NMEA data really unnecessary?
Many NMEA instruments output a large number of
sentences every period (usually 1-3 seconds), some of
this data is of absolutely no use to the average boat owner,
and just clogs up the NMEA network. Most GPS units are
especially guilty of this and not all allow the user to reduce
the number of unwanted sentences that are transmitted.
Of those that do, the procedure can often be tricky and
time consuming.
The Actisense™ NDC-4 can lter the incoming NMEA
data to remove any sentences deemed unnecessary.
For example, most GPS units automatically output the
‘GSV’ sentences (normally 2 but could be as many as 4),
which give details of all the satellites that are currently in
view. All of this information is of no use to 99% of users,
but this alone can use up to 5% of the available NMEA
bandwidth/capacity.
The Actisense™ NDC ‘Inclusion List’ default is to allow all
sentences through. The user can modify these lists using
a simple ‘tick-box’ panel from within the Control Centre.
How to change the Inclusion Lists
The Inclusion List conguration tab consists of two groups
of sentence tick boxes, a box indicating the total number
of selected sentences, an NMEA channel selection pull-
down list, and Get from hardware, Reset to defaults and
Send to Hardware control buttons (refer to Figure 13).
Channel selection list:
Determines which input channel (port)
has its Inclusion List displayed for
editing with the tick-box controls in the
main section to the left.