NMEA Data Combiner
NDC-3-B
User Manual
Issue 1.31
Multiple talker interface for use with the NMEA 0183 standard.
Serial-data networking of marine electronic devices / instruments
Personal computer (RS232) interface to NMEA 0183 standards
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NMEA Data Combiner - NDC-3-B
Contents
© 2005 Active Research Limited
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Actisense™
Important Notices
Foreword
The Actisense™ NMEA Data Combiner (NDC-3) is Actisense™ recognises that instructions are often
intended for use in a marine environment, primarily for skipped, so we have aimed to write this document in an
below deck use. If the unit is to be used in a more severe informative, yet direct manner that will aid the user. We
environment, such use may be considered misuse under have tried to cover all the points a typical user may need to
the seller’s warranty.
know. Please read all sections before installing and using
the Actisense™ NMEA Data Combiner product and any
The Actisense™ NMEA Data Combiner (NDC-3) has been related software programs.
certified to comply with the European directive for Electro-
Magnetic Compatibility (EN60945), and is appropriately CE
marked. Operation of the unit should be in conjunction with
appropriate CE approved shielded connectors and cabling
Introduction
The Actisense™ NMEA Data Combiner (NDC-3) product
used in accordance with the CE directive EN60945. Any
EMC related issues should be reported to Active Research
immediately to allow the company to rectify or resolve
EMC related problems in accordance with its obligations
under EN60945.
developed out of the requirement to solve two fundamental
problems with the existing marine industry NMEA 0183
communications standard.
In theory, the NMEA 0183 standard allows any suitably
designed marine electronic device to share its gathered
informationwithanyotherdeviceonavessel.Unfortunately,
there is one very large drawback with this standard - only
one device on a connected network can actually send
data (a single talker), with multiple devices (determined by
the current limit of the sending unit) listening to that data
(multiple listeners).
If the unit is connected such that compliance failure occurs
beyond the company’s control, the company shall not be
held responsible for compliance failure until suitable EMC
guidelines for connection are seen to have been taken.
Notices
When using this document, keep the following in mind:
If the vessel owner has an instrument that ideally requires
the data output of two or more devices, for example a chart
Theproductsdescribedinthismanualandthespecifications plotter, then the owner has no alternative but to settle on
thereof may be changed without prior notice. To obtain up- connecting only the most important device (that which
to-date information and/or specifications, contact Active supplies the most used information), normally that is the
What happens if the owner prefers the vessels gyro
compass heading output to that of the GPS, or requires
that the current depth be displayed on the plotted chart to
help avoid the possible case of running the vessel aground
on a shifting sand bank? The NMEA 0183 standard cannot
supply an answer to those questions as it can handle only
one transmitting device.
Active Research Limited will not be liable for infringement
of copyright, industrial property right, or other rights of a
third party caused by the use of information or drawings
described in this manual.
All rights are reserved: The contents of this manual may
not be transferred or copied without the expressed written
permission of Active Research Limited.
These two elementary problems can be solved simply and
easily with the Actisense™ NMEA Data Combiner’s very
flexible design approach.
Active Research Limited will not be held responsible for
any damage to the user that may result from accidents
or any other reasons during operation of the user’s unit
according to this document.
Alternately, if the vessel has two or more identical NMEA
devices (e.g. GPS’s or depth sounders) the system solution
could be to use the Actisense™ NMEA Autoswitch.
The NDC-3 does not validate the NMEA data it receives
in any way. Neither the NMEA sentence checksum, nor
the data contained within the NMEA sentence is validated.
Therefore, the electronic device(s) supplying the NDC-3
with NMEA data retain(s) the sole responsibility for the
NMEA data’s validity.
Full information on the complete Actisense™ product
© 2005 Active Research Limited
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NMEA Data Combiner - NDC-3-B
Full specification RS232 interface ensures that any
marine electronic device (or PC) that has an RS-232 port
receives all the input NMEA data, and can add its own
NMEA data to the combined output. This connection also
allows the unit to be updated via the free flash upgrade
software that will be made available on the Actisense™
website if the NDC-3 software has been enhanced.
General features
4 NMEA 0183 data input ports
Each NMEA0183 input port has a priority level. This is fixed
to the logical order that matches the port numbers, i.e. port
1 has the highest priority and port 4 has the lowest.
An NMEA 0183 data combined output port
Wide battery input voltage range to offer maximum
compatibility, the NMEA 0183 NDC-3 can operate from a
battery supply anywhere between 8 and 35 volts.
This output combines the input data into one standard
NMEA output. The NMEA inputs and output have the same
baud rate. This means that the output can only carry as
much data as one of the inputs - therefore the combined
data from all four NMEA input channels could exceed the
data carrying capacity of the NMEA output channel. The
combiner contains special software to ensure that when
the output channel is overloaded, new data of the same
type as older data, still in the buffer, will overwrite the older
sentence. This will only happen when the output load
becomes too high, and ensures that the combiner cannot
build up excess old data in the case where the output
stream is fully loaded or overloaded.
Low Power Consumption that is typically 26-30mA at 12
volts and 16-18mA at 24 volts.
A diagnostic LED indicates the operation mode of the
NDC-3, if any faults have been detected, or the peak load
currently on any one of the NMEA inputs.
Very tough Polycarbonate case is certified to IP66
(classified as “totally protected against dust and protection
against low pressure jets of water from all directions”).
Being Polycarbonate, it is also incredibly strong, offering
a wide temperature range and superior protection to the
electronics inside. The IP66 rating of the case is only
limited by the sealing gasket strip, which can be enhanced
by applying a suitable non-acid based marine sealant to
the gasket after wiring and testing. This will allow use of
the unit in areas where salt spray could enter, accidental
immersion may occur, or in environments where maximum
long-term reliability is paramount.
A PC compatible RS-232 bi-directional port
A PC can use the RS-232 port to read all the NMEA data
traversing through the NDC. This allows for the possibility
of a “virtual cockpit” of instruments displaying all available
data in any manner the user requires (available from a
number of manufacturers).
Technical features
Robust Nylon grommets are certified to IP68 (classified
as immersible for long periods without water ingress). Note
that to achieve this level of water integrity all grommets
must be occupied by round-section cables.
High-speed micro-controller capable of 10 million
instructions per second.
Flash ROM technology that supports automatic
programming for quick and easy updates, 10,000+ erase
cycles and a 10-year Data Retention provides carefree
user configuration.
Large range of possible cable diameters of between
4.5 mm and 10 mm, single or multi-pair wire types can be
easily accepted.
On-chip memory store allows buffering of short term
NMEA data, allowing the unit to smooth short-term peaks
in the NMEA data flow.
Software updates
The NDC-3’s built-in firmware is held in “flash” memory,
allowing quick and easy upgrades using a simple Microsoft
Windows (95/98/ME/NT/2000/XP) user interface program
(Flash Centre) running on a connected PC.
NMEA 0183 inputs are opto-isolated differential inputs to
fully comply with the NMEA 0183 standard specification.
This allows the inputs to work correctly with long cable runs
and in a noisy environment. Typical operating voltage is
2.0v to 15.0v. The unit can withstand +/- 35v continuously,
and +/- 40v transients. The Opto-isolator can protect any
upstream equipment (chart plotter, laptop PC, radar etc.)
from up to 2000v of common mode voltage difference.
It is our policy to provide these updates free on our website,
www.actisense.com, so that your combiner can become
more sophisticated with time, and should there be any
bugs reported in the software, they can be promptly fixed
without the unit coming out of commission. This upgrade
can be performed with the unit completely in-situ, via a PC
connected to the RS232 port.
NMEA 0183 full-differential output driver. This can drive
up to 15 fully compliant NMEA 0183 device loads, with a
30mA (maximum) drive capability. The full-differential
output ensures better quality communications and lower
noise emissions on unshielded twisted pair cabling.
© 2005 Active Research Limited
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Actisense™
Connecting devices together
The basics
The different NMEA standards
The NMEA 0183 specification has slowly evolved over the
years, so connecting one device to another is not always a
straightforward matter. The earlier versions of NMEA 0183
(before v2.0, as detailed above), used slightly different
connection methods and signal levels: the instruments
had just one “NMEA” data line (‘Tx’ or ‘Out’), and used
the ground as the other line - similar to the way a computer
serial port works. This connection method is referred to as
“single ended” instead of the “differential” method used by
NMEA 0183 v2.0 devices.
NMEA data is transmitted from an information source such
as GPS, depth sounder, gyro compass etc. These data
sending devices are called “Talkers”.
Equipment receiving this information such as a chart-
plotter, radar or NMEA display is called a “Listener”.
Unfortunately, only one Talker can be connected on to a
single NMEA 0183 system at any one time. Two or more
Talkers are simply not possible because they are not
synchronised to each other, and will attempt to ‘talk’ at
the same time (over each other), resulting in corruption of
the NMEA data, and potentially in disaster if valuable data
such as navigation information is lost or corrupted so that
it is incorrect and/or misleading.
The data format is largely the same between both
systems, with v2.0 adding some extra sentence strings,
and removing older (redundant) sentence strings from the
specification. The situation is further complicated, as many
manufacturers still use the old (“single ended”) method of
connection because it is cheaper to implement.
Actisense™ produces a full range of products to solve all
NMEA interfacing requirements.
So how can an older type NMEA device be connected to a
newer type device?
these and other Actisense™ interfacing, Depth sounding
and Sonar products.
Care is needed – it is possible to damage or overload
the output of a newer differential device if it is incorrectly
connected to an older device. This is because the older
devices used ground as the return, whereas the newer
devices actually drive the NMEA “-/B” line between 5v and
0v. Thus, connecting this output to ground will result in high
currents being drawn by the driver instrument, resulting in
potential overheating and damage to the driver circuits.
The NMEA signals
The NMEA 0183 system v2.0 and later uses a ”differential”
signalling scheme, whereby two wires are used to transmit
the NMEA data. These connections will be labelled as
either NMEA “A” and “B“ or NMEA “+” and “-“ respectively,
depending on the instrument and manufacturer.
To connect a new type differential device to an old type
single-ended system, connect the NMEA “+/A” output from
the differential driver to the single-ended NMEA“Rx” or “In”
input of the device. Leave the NMEA “-/B” output floating.
Connect the ground line of the differential output device to
the ground of the single-ended device. This provides the
required data signal return current path.
When connecting between different manufacturers, there
can be some confusion, but it is simple and easy to
remember: NMEA “A” connects to NMEA “+” and NMEA
“B“ connects to NMEA “-“.
To connect an old type single-ended device to a new type
differential device, connect the NMEA ”Tx” or “Out” output
from the single-ended driver to the differential NMEA
“+/A” input of the device. Connect the ground line of the
single-ended output device to the NMEA “-/B” input of the
differential device. This provides the data signal return
current path. If the NMEA “-/B” input is left floating, then
data corruption / errors may occur.
Please refer to the Output Connections section for
example of these connection methods.
© 2005 Active Research Limited
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NMEA Data Combiner - NDC-3-B
Connections
Figure 1 – All external connections
The NMEA Data Combiner (NDC-3) has screw-terminal “Phoenix” type external connections for: -
1. Four NMEA 0183 inputs.
Note:
All NMEA 0183 inputs are of the differential opto-
isolated type and use the unique Actisense™ low
current drain circuitry (2mA @ 2.0v) to conform in full
with the NMEA0183 marine electronic device network
communication standard, and are flexible enough
to interface to most fully and partially compliant
devices.
1. To complete the NMEA 0183 standard all device
interconnection NMEA cables used should meet the
two-conductor, shielded, twisted pair configuration
specification. The shield connection of these wires
should be connected at the instrument end only to
prevent ground loops.
2. Refer to the Specifications section for the full details
2. An NMEA (data combined) 0183 output.
The NMEA 0183 output comprises of three
connections: ‘+’, ‘-‘ and ‘Ground’ and conforms in full
to the NMEA 0183 standard. This allows the NDC to
interface to various different devices that require any
combination of these outputs.
on input/output specifications.
3. If the laptop / PC to be used with the NDC does not
have an RS-232 serial port available, the Actisense™
USB to RS-232 adapter cable has been tried and
tested to provide a compatible communications port.
on this, and other Actisense™ products.
3. An RS-232 input/output.
The bi-directional RS-232 port is designed for direct
connection to a Personal Computer (PC) or other
marine device capable of interfacing to a standard
RS-232 port.
4. Battery supply input.
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Actisense™
Connecting to NMEA devices
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Figure 2 – NMEA 0183 connections
NMEA 0183 Inputs
NMEA 0183 Output
The NMEA 0183 differential opto-isolated inputs are The NMEA 0183 buffered output is capable of driving up
designed to handle a variety of NMEA 0183 device to 15 NMEA 0183 fully compliant listening devices, or a
output specifications. Please determine (from device mixture of NMEA 0183 devices and a Personal Computer
manufacturer’s information) if the device(s) required to (PC) communication port.
be connected to the Actisense™ NDC-3 conforms in full
to the NMEA 0183 network communication standard. If it
does not, the flexible Actisense™ NDC-3 inputs should
still be capable of interfacing with the device, though this
is not guaranteed.
NMEA Listener device’s B and C: These devices
conform in full to the NMEA 0183 standard and their
connection ID’s match that of the NDC.
PersonalComputer:WhilsttheRS-232portisdesigned
for connection to a PC, the NMEA 0183 output is also
capable of being read by most PC’s. Simply connect ‘+’
to ‘Rx’ and ’G’ to ‘Gnd’ on a standard D-type (probably
male) connector.
The diagram above shows a typical installation with both
fully compliant NMEA devices with differential inputs/
outputs, and non-differential output devices that output
NMEA using the ground line as the “NMEA -” line.
NMEA Talker devices 1, 2 and 4: These devices
conform in full to the NMEA 0183 standard. Devices
1 and 4 share the same connection ID’s as the
Actisense™ NDC, so connection is a simple matter of
matching the ID’s (refer to figure 2). Device 2 uses the
RS485 convention connection ID’s. Simply connect ‘A‘
to ‘+/A‘ and ‘B’ to ‘ -/B’ (refer to figure 2).
NMEA Listener device A: This device does not
conform in full to the NMEA 0183 standard. However,
by connecting ‘-‘ to ‘-/B‘ and ‘G/Ground’ to ‘Gnd’
the device should be able to receive the NMEA data
correctly, though this is not guaranteed.
Note:
1. Wire colours are for guidance only.
NMEA Talker device 3: This device does not conform
completely to the NMEA 0183 standard. However, by
connecting ‘+‘ to ‘+/A‘ and its ‘G/Ground’ to the NDC
“-/B” the NDC should be able to receive the NMEA data
correctly.
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NMEA Data Combiner - NDC-3-B
Other Connections
NMEA DATA COMBINER
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NDC-3-B
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Figure 3 – RS-232 and Battery connections
Connecting to a Personal Computer
Connecting to the battery supply
TheRS-232portcanbeconnectedtoaPCcommunications
port using
a
cable conforming to the following
The Actisense™ NDC-3 should be wired to the vessel’s
battery supply in the most direct manner possible, to
minimize interference from other electronic devices. The
cable used should be of sufficient gauge to handle the
power requirements of the Actisense™ NDC-3 (refer to
the Specifications sections).
specification:
1. A D-type female (socket) connector for the PC end of
the cable
2. A minimum of 3 cores are required in a shielded
cable. Higher quality cable will naturally yield higher
performance / higher Signal-to-Noise Ratio (SNR).
Most typical cables have two twisted pairs inside. In
this case, use one pair for the TX line and one for the
RX line. Use the spare wire in each pair as ground,
and connect the cable shield to ground only at the
computer end.
Note:
1. Wire colours are for guidance only.
3. The TX of the NDC-3 should be connected to the
RX of the computer (standard D-type, pin 2) and
the NDC-3 RX should be connected to the TX of the
computer (pin 3). The GND of the NDC-3 should be
connected to the PC’s serial port ground (pin 5).
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Actisense™
Troubleshooting guide
This guide will concentrate on all relevant troubleshooting issues above simple cable connection faults. Therefore, the
cables between the NDC-3 hardware and any other devices should be checked as a matter of course, before continuing
with this guide.
Diagnostic LED
The NDC-3 hardware supports a tri-colour diagnostic LED that indicates the current operating mode of the hardware, or
if an error has been detected during the self-test initiation process. Table 1 details what each LED colour represents and
if any user interaction is required.
LED Colour /
Flash Count
Mode / Error condition
Required user response
The sequence below indicates a successful power-up of the
NDC-3 and the commencement of data combining.
Normal operation modes
No response required. A normal operation mode that should
last for no more than 1.5 seconds. Any longer indicates an
error with the main program.
Red,
No flashing
Start-up mode,
No error
No response required. LED will stay red for the duration of the
flash update operation (using Flash Centre). Once operation
complete, NDC hardware will be automatically reset.
Red,
No flashing
Flash updating mode,
No error
No response required. A normal operation mode that follows
after the Start-up mode and should last for approximately 1
second.
Amber,
No flashing
Initialise and self-test mode,
No error
No response required. A normal operation mode that follows
the Initialise and self-test mode. Indicates that no error was
detected during the self-test operation.
Green,
No flashing
Normal and no data mode,
No error
Also indicates that no data is currently being received by the
NDC-3 hardware.
Green,
Flashing
(1-10 per second)
No response required. A normal operation mode that indicates
that data is currently being received (on at least one channel)
by the NDC-3 hardware. Flash rate proportional to Rx rate.
Normal and data Rx mode,
No error
If the error persists the NDC-3 unit should be returned to
Actisense™ (refer to the Contact Information section).
Error conditions
Amber,
Flashing
An error with the EEPROM memory has been detected during
the self-test mode.
Error trap mode,
(Once every 4
seconds)
EEPROM memory error
Reset the NDC-3 hardware.
Table 1 – Diagnostic LED colours
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NMEA Data Combiner - NDC-3-B
Specifications
Parameter
Supply
Conditions
Min.
Max.
Unit
Supply voltage
8
35
30
18
V
Supply voltage = 12v
Supply voltage = 24v
26
16
mA
mA
Supply current (see note 1)
NMEA
Logical ‘1’/stop bit
Logical ‘0’/start bit
-15.0
4.0
0.5
V
V
Input voltage between +/-
15.0
Maximum is under +35v overload
condition
Required level for NMEA to be
detected
Input current
2.0
1.8
30
mA
V
Differential input voltage
2.0
Logical ‘1’/stop bit
0.0
4.8
0.5
5.2
V
V
Output voltage between +/- and ground
(see note 2)
At maximum load, drive voltage
reduces to 2v
Output current (see note 2)
-
32
mA
Output short circuit current.
Baud rate - fixed (see note 3)
Data propagation delay
RS-232
50
55
4.8
100
mA
kbit/sec
ms
1.0
Input voltage range
-15
0.8
1.7
±5
+15
1.2
2.8
±9
V
V
LOW
Input voltage threshold
HIGH
V
Output voltage swing
Output resistance
Loaded with 3κΩ to Ground
(RS232 Vout = ±2v)
V
300
Ohms
Output short circuit current
(Infinite duration)
±18
mA
Baud rate (see note 4)
Data propagation delay
38.4
100
kbit/sec
ms
1.0
-20
General
Ambient temperature
+70
°C
Table 2 – NDC-3 specifications
All specifications are taken with reference to an ambient temperature (TA) of +25°C.
Note:
1. Current consumption measured under no-load conditions
2. NMEA output is RS-485 compatible.
3. NMEA 0183 inputs and outputs on the NDC-3 are fixed to 4800 baud
4. RS232 baud rate is fixed at 38400 baud on the NDC-3
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Actisense™
Company Information
Active Research Limited
5, Wessex Trade Centre
Ringwood Road
Poole
Dorset
UK
BH12 3PF
Telephone:
Fax:
01202 746682 (International : +44 1202 746682)
01202 746683 (International : +44 1202 746683)
Actisense™ on the Web: For advice, support and product details
E-mail:
Website:
Active Research on the Web: For specialist consultancy and customisation
E-mail:
Website:
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