ShipModul MiniPlex-2USB NMEA-0183 User manual

MiniPlex-2USB NMEA 0183 multiplexer
Manual
MiniPlex-2USB, V2.0
Firmware V3.00
Art.no.: 1121
Man. rev. A
© CustomWare, 2011

2
Introduction ....................................................................................................................... 3
Talkers and Listeners ........................................................................................................ 3
The Multiplexer ................................................................................................................ 3
The MiniPlex-2USB............................................................................................................ 4
Connections........................................................................................................................ 5
NMEA Signals................................................................................................................... 5
NMEA Listener Ports/Inputs ............................................................................................... 5
NMEA Talker Ports/Outputs................................................................................................ 5
Combining Ports ............................................................................................................... 6
SeaTalk........................................................................................................................... 7
USB port ......................................................................................................................... 7
Power Supply ................................................................................................................... 7
Driver Installation ............................................................................................................... 8
Windows 2000/Vista/XP Installation.................................................................................... 8
Windows 7 Installation ...................................................................................................... 8
Mac OS X Installation.......................................................................................................14
Data Troughput..................................................................................................................15
Configuration .....................................................................................................................17
Menu .............................................................................................................................18
Controls .........................................................................................................................19
Communication Port......................................................................................................19
Read Configuration .......................................................................................................19
NMEA Input settings......................................................................................................19
NMEA Output setting .....................................................................................................20
Options .......................................................................................................................21
Mode of Operation ........................................................................................................22
Sentence Filter .............................................................................................................23
Manual NMEA input .......................................................................................................24
Firmware Update................................................................................................................25
Indicators..........................................................................................................................25
Mounting...........................................................................................................................25
Technical Reference............................................................................................................26
Firmware Update Error messages ......................................................................................26
MPX-Config Registry keys .................................................................................................27
MPX-Config INI file format ................................................................................................27
Proprietary NMEA commands ............................................................................................28
Proprietary sentence definitions.........................................................................................28
VER – Get Version.........................................................................................................28
CN - Channel Number indicator ......................................................................................28
CF – Configuration ........................................................................................................29
CFQ – Request current configuration ...............................................................................29
SP – Speed ..................................................................................................................30
SPQ – Request Speed....................................................................................................30
FL – Filter ....................................................................................................................30
FLQ – Request filter list .................................................................................................30
ID – Talker ID ..............................................................................................................31
IDQ – Request Talker ID’s..............................................................................................31
OV – Overflow ..............................................................................................................31
RESET – Reset the multiplexer .......................................................................................31
LDR – Loader message ..................................................................................................31
Translated SeaTalk datagrams ..........................................................................................32
Technical Specifications.......................................................................................................33
Declaration of Conformity....................................................................................................34

3
Introduction
The MiniPlex-2USB is an NMEA multiplexer that enables the connection of multiple NMEA 0183
instruments to each other and a computer. It is developed to solve a fundamental problem with the
NMEA 0183 standard.
The NMEA 0183 standard defines a communication protocol that enables navigation instruments to
exchange data with each other. A compass can send a bearing to a radar to enable a north-up
display, a GPS can send cross-track information to an autopilot in order to steer a programmed
course. The same GPS can also send information to the radar at the same time since the NMEA
0183 standard specifies that one device must be able to send data to up to four other devices.
NMEA data is made up of short text messages with a strict format called sentences and are human-
readable.
Talkers and Listeners
Communication using the NMEA 0183 protocol involves at least one
device that sends NMEA sentences and another device that receives
NMEA sentences. By convention, a sending device is called a talker while
a receiving device is called a listener. The picture on the right shows
such a minimal system: a gyrocompass sending heading sentences to a
radar.
The NMEA 0183 standard specifies that a talker should have enough driving capability to talk to
four listeners. This is as easy to achieve as telling a story to an audience of up to four people. The
only requirement is to talk loud enough.
The picture left below shows such a situation.
GPS
PC
VHF
Radar
Auto-
Pilot
Plotter
GPS
Depth
Wind
Compass
It gets complicated when several talkers must send data to one listener as shown in the picture on
the right. Unless that listener has multiple inputs, this is not possible without help. Simply
connecting talkers to one listener as shown is like four persons simultaneously telling you a
different story. You can’t make head or tail of it. In electronics terms: the outputs of the talkers will
effectively short-circuit each other and the sentences they transmit will be corrupted. This is where
a multiplexer offers the solution.
The Multiplexer
A multiplexer, sometimes called ‘combiner’, has multiple inputs, each acting as a single listener
connected to a talker. It can also have several outputs are able to talk to multiple listeners. A
clever piece of software inside the multiplexer reads the NMEA sentences that are received on the
listener ports simultaneously and stores them into queues. Another part of the software retrieves
the sentences from the queues, one at a time, and sends them to the outputs of the multiplexer.
This way, four incoming streams of sentences are combined into one single stream.
Gyro Radar

4
The picture below shows a typical setup with a multiplexer combining data from a wind instrument,
a compass and a GPS and forwarding this data to a laptop and an autopilot. In this example, the
multiplexer has two types of outputs: an NMEA talker port called ‘Out1’ and a USB port to connect
to a computer. The multiplexer sends the received NMEA sentences to both the laptop and the
auto-pilot at the same time.
The USB connection with the laptop is actually bi-directional: the laptop acts as a listener and a
talker at the same time. It receives NMEA sentences from the instruments to be processed by
navigation software that is running on the laptop. This software can also generate NMEA sentences
to control an auto-pilot. These sentences are sent to the multiplexer, which in turn sends them to
the auto-pilot. These sentences can be combined with the ones received from the other navigation
instruments.
Wind
Multiplexer
Com-
pass
GPS
Laptop
Auto-pilot
In 1
In 2
In 3
USB
Out 1
The MiniPlex-2USB
The MiniPlex-2USB is a multiplexer with four NMEA inputs (listener-ports), two NMEA outputs
(talker-ports) and one USB port to connect to a computer. The multiplexer combines NMEA data
that is received on the listener ports In1 to In4 and sends this data to talker ports Out1 and Out2
and to the USB port. This USB port is also used to send data from a computer to the multiplexer to
be forwarded to Out1, as well as to send commands to configure the multiplexer.
Every NMEA input on the MiniPlex is galvanically isolated, sometimes called opto-isolation because
of the use of opto-couplers for isolation. An opto-coupler is a small device that transports
information by means of light instead of electricity.
A galvanically isolated input prevents unwanted currents to flow between instruments and the
multiplexer. These currents can damage equipment or interfere with radio signals and should
therefore be avoided. Galvanically isolated inputs are required by the NMEA standard.
The USB port of the MiniPlex is also galvanically isolated, which isolates the computer from the
navigation network and protects it against potential damage caused by ground loops or voltage
spikes.
Both NMEA outputs can drive up to four listeners each. They are slightly different from each other:
Out1 is meant to be connected to an auto-pilot and repeater displays while Out2 is more suitable
to deliver data to a chartplotter. This will be explained later.
Besides the basic functionality of combining NMEA data from multiple sources, the MiniPlex offers a
range of features to manage NMEA data like Sentence Filtering, Input Priority with automatic
switchover, testing of data integrity, Talker ID modification and SeaTalk®to NMEA translation.
The MiniPlex can seamlessly be integrated into an existing Raymarine SeaTalk network when
SeaTalk mode is enabled. This mode changes one NMEA listener port into a SeaTalk input. When
connected to a Raymarine SeaTalk network, the multiplexer will translate SeaTalk data into NMEA
sentences and combine these with NMEA sentences that are received on the other listener ports.
Only one SeaTalk input is needed since the SeaTalk bus is a single-cable system that connects all
instruments together through one single cable. SeaTalk to NMEA translation in the MiniPlex works
only one way. No NMEA sentences are converted into SeaTalk, the multiplexer is just listens on the
SeaTalk bus.

5
Connections
NMEA Signals
Although the NMEA 0183 standard very clearly specifies the signal names, voltage levels and
connection methods, the reality is far from this ideal world.
The most important property of an NMEA port is that the connections or wires are labelled ‘A’ and
‘B’ and that it uses a differential signalling scheme. This means that data is transmitted on both
wires, but in ‘opposite direction’. Both wires are driven between 5V and 0V and opposite of each
other. This means when A is 5V, then B is 0V and vice versa. The advantage of this signalling
scheme is that it is very insensitive to electrical interference. NMEA ‘A’ and ‘B’ are often labelled as
NMEA ‘+’ and ‘-’ respectively. When connecting devices, simply connect NMEA ‘A’ to NMEA ‘A’ or
NMEA ‘+’ and NMEA ‘B’ to NMEA ‘B’ or NMEA ‘-’.
Things get complicated when manufacturers don’t follow the NMEA 0183 standard, which is very
often the case. Many devices have an NMEA port, which is really an RS-232 port. The only
resemblance with the NMEA standard is the format of the data transmitted. Electrically, they are an
entirely different world. The used signal names differ wildly and often lead to confusion. When a
device has a listener port with connections ‘Data In’ and ‘Data Return’ it is not clear whether this
input is galvanically isolated or ‘Data Return’ is simply another name for ‘Signal ground’
As opposed to the NMEA standard, many devices use a single-ended signalling scheme where data
is transmitted on one signal wire while a power/signal ground presents the return path for data.
Single ended devices often have connections named as TX and Gnd (transmit and ground) on the
talker port and RX and Gnd (receive and ground) on the listener port. Also used are Data Out, Data
In and Signal Ground. Mix these with ‘standard’ NMEA connections and confusion is imminent!
In general it is safe to connect a single ended talker port to a differential listener port. Connecting
a differential talker port to a single ended listener port however is less obvious. When NMEA ‘B’ of a
talker port is connected to the signal ground of a listener port, the ‘B’ signal is effectively short-
circuited to ground. A properly designed talker port can handle this abuse but it will result in fairly
high currents in long cables, which in turn leads to severe interference on SSB radios and possibly
on VHF radios too. In the worst case, the talker port will be destroyed.
To overcome this problem, the MiniPlex multiplexers provide a Com terminal on each talker port in
addition to the ‘A’ and ‘B’ terminals. This ‘Com’ terminal is similar to a signal ground. To connect a
talker port of the MiniPlex to a differential NMEA listener port, use the ‘A’ and ‘B’ terminals. Use the
‘A’ and ‘Com’ terminals to connect to a single-ended or RS-232 listener port.
NMEA Listener Ports/Inputs
The multiplexer has four listener ports, In 1 to In 4. Each listener port should be connected to one
instrument only. These inputs are completely floating and galvanically isolated from the
multiplexer, as specified in the NMEA 0183 standard.
Connect the Aand Bterminals of the listener port on the multiplexer to the Aand Bterminals of
the talker port on the instrument. These terminals may also be labelled as Data+ and Data-, TX+
and TX- , Out+ and Out– or ve+ and ve-.
Some instruments have single ended talker ports, with only one data terminal. Connect this
terminal to the Aterminal on the multiplexer, and connect the ground of the instrument to the B
terminal on the multiplexer. The instrument’s data ground is often combined with its power supply
ground.
Instrument Multiplexer Instrument Multiplexer
TX
Ground
Differential Single-ended
Out A / +
Out B / -
In A
In B
In A
In B
NMEA Talker Ports/Outputs
Both talker ports can be connected to up to four instruments. Connect the Aand Bterminals of the
talker port on the multiplexer to the Aand Bterminals of the listener port(s) on the instrument(s).
These terminals may also be labelled as Data+ and Data-, RX+ and RX- , Out+ and Out– or
ve+ and ve-.

6
Some instruments have single ended listener ports, with only one data terminal. Connect this
terminal to the Aterminal on the multiplexer, and leave the Bterminal on the multiplexer
unconnected. Connect the ground of the instrument to the Com terminal on the multiplexer. The
instrument’s data ground is often combined with its power supply ground.
Multiplexer Instrument Multiplexer Instrument
Differential Single-ended
RX
Ground
Out A
Out B
Out A
Out B
In A / +
In B / -
ComCom
Multiplexer
Out A
Out B
Com
Instrument
In A / +
In B / -
Instrument
RX
GND
Instrument
In A / +
In B / -
Multiple instruments
The shield terminals on the multiplexer (Shld) can be connected to the screen/shield of the cable if
available. This should always be done on one end of the cable only, preferably on the end that is
connected to a talker port.
Combining Ports
It is sometimes necessary to combine a listener and talker port of the multiplexer to connect to an
instrument. One of the most commonly used combinations is the connection of a GPS to the
multiplexer. While some GPS receivers have properly designed NMEA ports, many only have an
RS-232 port which is single ended with three terminals: TxD (data out), RxD (data in) and Ground.
The picture below shows how to connect such a GPS to the multiplexer.
Multiplexer
Out1A
Out1B
In1B
In1A
Com
GPS
RxD
Ground
TxD
Connecting a GPS with an RS-232
port

7
SeaTalk
SeaTalk®is a proprietary protocol developed by Raymarine®. This protocol is used for
communication between Raymarine navigation instruments like the ST40, ST50 and ST60 series.
To be able to use these instruments with commonly available navigation programs or to feed their
data into other non-Raymarine instruments, the SeaTalk data needs to be translated into NMEA.
Even Raymarine's own navigation software, Raytech Navigator, needs this translation.
The MiniPlex can be directly connected to a SeaTalk network. It will translate all SeaTalk data
required for navigation into NMEA sentences. Input In 4 can be set to SeaTalk mode
(SeaTalk -> NMEA) and should be connected as shown below:
SeaTalk cable
Multiplexer
Connecting a SeaTalk network
In 4A
In 4B
Red
Yellow
Note that the red and yellow wires are used! The screen of the SeaTalk cable is not connected to
the multiplexer.
USB port
The USB port connects the multiplexer to a computer or a USB hub with the supplied cable. The
supplied driver provides a virtual COM port to allow navigation software to communicate with the
multiplexer. The USB port is bi-directional: the multiplexer sends NMEA data to the computer and
the computer can also send NMEA data back to the multiplexer. This data is available on
NMEA Out 1.
The USB port is galvanically isolated from the multiplexer to prevent ground loops and excessive
currents that could otherwise destroy the multiplexer or the USB port of the connected computer.
The USB connection supports flow control which is needed when waypoints and routes are sent
from the computer to a GPS through the multiplexer. While normal NMEA sentences are sent at
regular intervals, waypoints and routes are sent ‘in one go’ without any pause between these NMEA
sentences. This fills up the queue in the multiplexer almost immediately after which the multiplexer
discards the remaining waypoints and routes. The GPS now only receives a few waypoints and
partial routes.
Flow control prevents this from happening. When the queue in the multiplexer is almost filled, the
multiplexer signals the computer to stop sending data. When the queue is sufficiently emptied, the
multiplexer signals the computer to continue. This requires a special setting in your navigation
software, which is mostly called ‘Flow Control’. This setting can mostly be found in the port settings
of your software. Set the Flow Control to Hardware or CTS/RTS. This Hardware flow control is
virtualized over the USB connection. Do not use Xon/Xoff flow controls since this uses special
characters instead of a (virtual) signal. These characters are not part of the NMEA standard and
therefore ignored by the multiplexer.
Power Supply
The multiplexer must be powered from an externally supplied DC voltage from 8 to 35V. The power
supply connection is protected against reversed polarity.

8
Driver Installation
To use the MiniPlex-2USB with your computer, a USB device driver needs to be installed. This
driver creates a virtual COM port, which can be opened with any navigation software just like any
other COM port. Drivers are supplied for Microsoft Windows (Windows 2000, Windows XP, Windows
Vista, Windows 7) and Apple’s Mac OS X.
Windows 2000/Vista/XP Installation
When the multiplexer is connected to a USB port for the first time, Windows will detect new
hardware and prompts you for a driver. Insert the supplied CD into the drive and follow the
instructions on your screen. Don’t let Windows search the internet for updated drivers. When asked
to automatically search for drivers, answer no and choose the option to tell Windows where to find
the driver. The driver can be found on the supplied CD, in de folder ‘USB Driver’. This folder
contains subfolders with drivers for various operating systems.
Windows will warn you that the drivers are not digitally signed and can pose a threat to the
stability of Windows. Just ignore that warning and continue with the installation.
The installation on Windows is a two-step process. First, the driver for the multiplexer will be
installed. Next, Windows will detect a USB Serial device and will install a second driver. On
Windows XP systems, there can be a delay of up to 10 seconds between the installation of both
drivers, which sometimes leads to the conclusion that the installation is complete after the first
driver is installed which is not the case. On Windows Vista and Windows 2000 systems, there is
only very little delay.
When the installation is complete, a new virtual COM port will be created. This COM port is shown
in MPX-Config as COMx (vcp) where ‘x’ is a number. Select this port in your navigation software.
The ‘vcp’ extension as shown in MPX-Config will not be visible in your navigation software.
If necessary, the number of this COM port can be changed in the Windows Device Manager. Click
on the ‘+’ sign next to the entry marked as ‘Ports (COM & LPT)’. This will expand the entry to list
all available COM ports on your computer. The port for the multiplexer is listed as ‘MiniPlex Serial
Port (COMx)’ where ‘COMx’ is the name of the newly created serial port.
To change this port number, double click on the MiniPlex Serial Port (COMx) entry to open the
property page for this port. Next, select the Port Settings tab and click on the Advanced…
button. In the appearing window the used port number can be changed. Do not change any other
setting in this window.
It is possible to select a port number that is already present on the computer, like COM1. The
original COM1 port will then be disabled as long as the multiplexer is connected to the computer.
This feature allows the port number to be set in a low range from COM1 to COM4, to accommodate
software that only allows COM1 to COM4 to be selected.
More than one multiplexer can be connected at the same time. Every new unit will create a new
virtual COM port. The number of the COM port will always be assigned to the same multiplexer
regardless of the USB port being used.
Windows allows a maximum of 256 COM ports. However not all software may be able to select
COM ports numbered above COM9.
When installing updated drivers, uninstall the original drivers first with the
Add/Remove Programs icon in the Control Panel or use the Update Driver button on the
Driver page of the MiniPlex Serial Port property-page.
Windows 7 Installation
Due to enhanced security measures in Windows 7, drivers are required to be digitally signed. When
a device is connected that has no digitally signed drivers, Windows 7 silently aborts the installation.
It is however possible to install the drivers anyway. Follow the procedure as described below to
manually install the MiniPlex drivers.
Connect the MiniPlex-2USB to the computer and ignore the warning ‘Device Driver software was
not successfully installed’.
Open Control Panel -> System and Security -> Device Manager.
In the Device Manager, there will be a ‘ShipModul MiniPlex-2USB’ listed under ‘Other Devices’ as
shown in the picture.

9
Rigth-click on the MiniPlex entry and choose ‘Update Driver Software...’ from the menu that
appears. This will open the following window:

10
Choose ‘Browse my computer for driver software’. In the following window, choose the location of
the driver and press ‘Next’.
Windows will now tell you it can’t verify the publisher of the driver software:
Choose ‘Install this driver software anyway’

11
When Windows has successfully installed the driver, the following window appears:
You can close this window.
The Device Manager will now list an USB Serial Port under Other Devices:

12
Rigth-click on the the USB Serial Port entry and choose ‘Update Driver Software...’ from the menu
that appears. This will open the following Window:
Choose ‘Browse my computer for driver software’. In the following window, choose the location of
the driver and press ‘Next’.

13
Windows will now tell you it can’t verify the publisher of the driver software:
Choose ‘Install this driver software anyway’
When Windows has successfully installed the driver, the following window appears:
You can close this window.

14
The Device Manager will now list a ShipModul MiniPlex NMEA Multiplexer under Universal Serial Bus
controllers and a MiniPlex Serial Port (COMx) under Ports (COM & LPT).
Mac OS X Installation
The OS X driver is available as a disk image file (.dmg) and can be found on the supplied CD in the
‘USB Driver’ folder. Run the installer by double clicking on the icon. Follow the instructions on the
screen and reboot the computer when asked.
When the computer has rebooted, plug in the multiplexer. Then open System Preferences and
select Network. You should now get the message ‘New Port Detected’. Click OK and select
Network Port Configurations from the ‘Show’ list. The new port will be listed as
MiniPlex-xxxxxxxx where ‘xxxxxxxx’ represents the serial number of the multiplexer. Enable the
port by checking the On box and clicking Apply Now. You can now exit Network and use the
multiplexer in your navigation software.

15
Data Troughput
Depending on the configuration of the multiplexer, NMEA sentences are sent to one or more talker
ports with different communication speeds. A situation could arise where more data is received
than can be transmitted because of the speed settings of the listener and talker ports. Such a
situation leads to an overflow of queues in the multiplexer. When an NMEA sentence is being
received while a queue is full, this sentence is discarded. Only complete NMEA sentences are stored
and forwarded. This event is indicated by the red LED, which will blink briefly when a sentence is
discarded.
The MiniPlex can be operated in two different modes called Server and Hub mode. These modes
determine the flow of NMEA data to Out1 and have a major impact on the data throughput. It is
therefore very important to understand the difference between these modes.
In Server mode, data received on the listener ports In1 to In4 is sent to the USB port while data
received on the USB port is sent to talker port Out1.
In Hub mode, data received on the listener ports In1 to In4 is sent the USB port and to talker
port Out1, combined with the data that is received on the USB port.
Out1A
Out1B
In1B
In1A
In2A
In2B
USB
Out2B
Out2A
In3A
In3B
In4A
In4B
Com
Com
Data path Server mode
Out1A
Out1B
In1B
In1A
In2A
In2B
USB
Out2B
Out2A
In3A
In3B
In4A
In4B
Com
Com
Data path Hub mode
The pictures above show the flow of NMEA data in both modes. As you can see in Server mode,
only a path exists from the USB port to Out1. In Hub mode, an extra path exists between the
inputs and Out1, indicated by the darker arrow in the middle. Out1 now outputs data that is
received on the USB port and on the NMEA inputs.
The path from the inputs to the USB port and Out2 is unaffected by the operating mode. These
ports always output data received on the inputs. Port Out2 can be used to send data to a
chartplotter.
This leads to the different purposes of Out1 and Out2: Out1 is mainly used to control an
autopilot. The auto-pilot needs steering information such as waypoint data, cross track error and
heading. This information can either come from a GPS connected to an input of the multiplexer
(Hub mode) or from a navigation program running on a computer connected to the USB port
(Server mode). When a computer controls the auto-pilot, there is no need to send data from the
inputs to the auto-pilot, possibly causing overflows because of the low speed of Out1 (4800 Baud).
Out2 on the other hand, is mainly used to send data to a chartplotter. Especially when an AIS
receiver or transponder is connected to the multiplexer, this output needs to be set to 38400 Baud.
Most chartplotters also support this high speed.
Now back to data throughput. The standard speed of an NMEA port is 4800 Baud or bits/second,
representing 480 characters per second. It is quite obvious that when four inputs receive data at
480 char/s and all of this data must be sent out again on an output with the same bandwidth of
480 char/s, a huge problem will arise. When the MiniPlex is set to Server mode, this problem is
quite easy to overcome: simply set the speed of Out2 to 19200 Baud (1920 char/s) or higher.
When Out2 is not used, set it to the highest speed. When it is connected to a chartplotter, try to
choose the highest speed the plotter will accept. In Hub mode however, the same data is also sent
to Out1 which usually operates at 4800 Baud to control an autopilot. There is our bottleneck again!
However…

16
NMEA data tends to be sent in bursts. Some devices line depth sounders or wind instruments only
send one sentence per second while a GPS may send bursts of up to 13 sentences every two
seconds. While the average throughput over time may be low, an input might fill its queue quite
rapidly when a burst of sentences is received. The queues in the MiniPlex are quite large and may
contain up to 30 sentences of GPS data.
A couple of occasional blinks of the red LED over a period of a few seconds means that large bursts
of sentences are received and a queue is hitting its limit. Some sentences are discarded but most
of them will be passed without problems. Such a situation is totally acceptable and would mean
that for instance one depth, wind or position update is missed every few seconds.
A quite different situation may arise with some fluxgates or gyrocompasses. These devices may
send their heading sentences with a speed up to 40 sentences per second! Instead of queuing a
burst of sentences every one or two seconds, the multiplexer must queue a constant stream of
sentences possibly utilizing the maximum bandwidth of the multiplexer. Such a situation can lead
to a queue that is constantly filled up to its maximum size. This in turn results in heading data that
can be up to 20 seconds old when it is forwarded, which is totally unusable for any autopilot to
steer on. This specific problem can be solved by enabling the Real Time option for this input. This
option bypasses the queue entirely. Only one sentence will be stored now and sent out when the
time slot for this input arrives. Outside its time slot, incoming sentences will be discarded. A lot of
heading sentences will be lost now but the ones that are passed, are passed almost immediately.
Hence the name ‘Real Time’.
When the red LED is blinking severely or stays on almost
continuously, it is advisable to investigate which instrument or
input leads to this overflow. The MPX-Config utility will show on
which input the overflow occurs by a blinking indicator in the
NMEA Input Settings section. Opening the Statistics window
from the Tools menu will give an insight about the amount of data
in a queue and whether it is filled constantly or occasionally.
Some general rules are applicable for reducing overflow situations.
A simple rule of thumb is that an overflow can never occur if the
speed of an output is equal or higher than the combined speeds of
all inputs. For example: if the multiplexer is in Server mode and
all four inputs are set to 4800 Baud, the minimum output speed
equals 4 x 4800 = 19200 Baud. This rule is only a hard rule when
the input bandwidth is fully utilized i.e. an instrument is sending
data continuously. This is hardly ever the case. As mentioned
earlier, NMEA data is often sent in bursts, resulting in a much
lower overall bandwidth. It could be perfectly feasible to have an
system with four instruments connected to the multiplexer, while
running all in- and outputs on 4800 Baud without a single
overflow.
There are several ways to resolve overflow situations:
1. Configure the instruments on the listener ports to send less data or with greater intervals.
GPS receivers can sometimes be configured for this.
2. Use the Sentence Filter of the multiplexer to block unwanted sentences. Unwanted
sentences are discarded immediately and do not occupy queue space or bandwidth.
3. For sentences that should not be blocked, the rate may be lowered by setting a divisor in
the Sentence Filter. A gyro may be ‘throttled down’ to 10 sentences per second or even
less. From the GPS output, the rate of the sentences containing satellite information could
be lowered to once every 10 seconds instead of being output every time a position is
output by the GPS.
4. Set the operation mode of the multiplexer to Server mode (factory default). This mode
only sends incoming data to the computer and to NMEA Out 2, which is factory set to high
speed (38400 Baud). In Hub mode, the high-speed ports must wait for every character to
be transmitted over any low speed ports.
5. Increase the speed of port Out 2 on the multiplexer, especially when this port is not used.
The maximum speed is 115200 Baud. From 19200 Baud and up (4 x 4800!) an overflow
will never occur, except when the multiplexer is set to Hub Mode.

17
Configuration
The multiplexer can be configured with a configuration program called MPX-Config. This program
can be found on the accompanying CD. There is no installation procedure for this program, just
start it from the CD or copy it to a suitable folder on the hard disk of your computer and start it
from there.
The multiplexer itself is configured with proprietary NMEA sentences. MPX-Config sends these
sentences to the multiplexer when you change a control on the screen.
All configuration settings are stored in the multiplexer’s non-volatile memory. These settings are
retained without power supply.
Screenshot of MPX-Config
The screen is divided into four sections from top to bottom: the menu, the data area, the control
area and the status bar. The menu basically controls the MPX-Config program. The data area
shows the NMEA sentences that are received from the multiplexer. These sentences include the
NMEA data received by the multiplexer on its inputs as well as status messages generated by the
multiplexer. The latter can be recognised fairly easy: they alls start with ‘$PSMD’. The control area
contains controls that determine the operation and configuration of the multiplexer. The status bar
shows the name or type of multiplexer that is connected, its internal software (firmware) version
number and its serial number. This information is useful when you need technical support. Also
shown are the optionally loaded or saved configuration file and a line counter when you have
started a log file.

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Menu
The menu contains two sub-menus: File and Tools. The File menu contains the following options
to choose from:
Start Log… Start writing NMEA data to a log file. A log file is a plain text file and
can later be opened by any text editor to examine the data. A log file
can be a useful tool for diagnostic purposes and is often requested by
us for support. If you enter a new filename in the file dialog window, a
new log file is created. If you choose an existing file, this file will be
overwritten with new data. The Log counter on the status bar will show
the number of NMEA sentences that are currently written to the log file.
Timed Log… Start writing to a log file with the addition of a time stamp at the
beginning of each NMEA sentence.
Stop Log Stop writing NMEA data to the current log file and close that file.
Load Configuration… Load a previously saved configuration file into the multiplexer. The
current configuration will be overwritten. A configuration file stores all
settings made with MPX-Config. See the Technical Reference section for
a description of this file format.
Save Configuration Save the current configuration to a file. If a file was previously opened,
that file will be overwritten. If no file has been opened before, you will
be prompted for a file name. The name of the currently loaded
configuration file is shown on the status bar.
Save Configuration As… Save the current configuration to a new file.
Update Firmware… Load new firmware into the multiplexer. From time to time, new
features are developed for the multiplexer or bugs are fixed. New
firmware image files will then be made available through our website.
These image files can be downloaded to your computer and loaded into
the multiplexer with this option. This option will only be visible when
your multiplexer supports firmware updates. This is the case from
firmware version 3.00 and up. Multiplexers containing lower firmware
versions need to be returned to our factory for an update.
Exit This option exits MPX-Config.
The Tools menu contains the following options to choose from:
Clear Screen Clear the data area on the screen. New sentences will be displayed
from the top.
No Scroll Normally, incoming NMEA sentences are displayed from the top down
and when the bottom of the data area has been reached, all sentences
are scrolled up one line before the new one is show. When No Scroll is
activated, a list of incoming NMEA sentences will be displayed that will
be refreshed constantly when new similar sentences are received. A
scroll bar will appear when the list grows beyond the length of the data
area. This feature allows you to closely examine the types of sentences
that are received from the connected instruments. Any proprietary
NMEA sentences that are generated by the multiplexer are also listed.
The can be recognised by the firsts four characters, which are ‘$PSMD’.
Show Statistics This option opens a new window that will be displayed on top of the
MPX-Config window. This window show bars that indicate how much
NMEA data is stored in the input queues. This is a useful option for
diagnosing data congestion and overflow situations as mentioned in
paragraph ‘Data Throughput’. A queue that is filled constantly can lead
to unacceptable delays in data transfer.
About Show a window with version information.

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Controls
The control area of the MPX-Config screen contains al the controls to configure the multiplexer.
When MPX-Config is started, it will retrieve the current settings from the multiplexer and set the
controls accordingly. If this query is unsuccessful, some controls will not be filled with values. This
could happen when the multiplexer was not powered up when MPX-Config was started.
Communication Port
Before being able to configure the multiplexer, select the
communication port to which the multiplexer is connected. The virtual
port created by the driver is marked with ‘(vcp)’. Since the speed
setting has no relevance to the speed of the virtual serial port, the
setting will show Automatic and will be disabled once the current
configuration has been retrieved from the multiplexer.
If you exit MPX-Config, the port setting will be saved on your computer.
Read Configuration
Clicking this button will request the current configuration settings from the
multiplexer. MPX-Config will do this automatically when started but the very
first time, when no port has been selected, you need to do this manually after
selecting the communication port.
When the wrong port is selected, MPX-Config will respond with a ‘Multiplexer does not respond’ -
message and all controls will be disabled (greyed).
The status line on the bottom of the MPX-Config window will show the name of the multiplexer, the
internal software (firmware) version and the serial number.
NMEA Input settings
This section allows you to set various options for
each of the inputs of the multiplexer. The
settings of each input are grouped together in a
horizontal section.
Speed
This sets the speed of each NMEA input in a
range from 4800 to 57600 Baud. 4800 Baud is
the standard speed for navigation equipment.
Some fluxgate or gyrocompasses operate at
9600 Baud to accommodate the higher
throughput of 20 headings per second or more.
AIS equipment operates at 38400 Baud.
If you change the speed of In4, the speed of
Out1 will be changed too. In 4 and Out 1 share the same communication port inside the
multiplexer and therefore always have the same speed. Out 1 is generally used to control an
autopilot and should be left at 4800 Baud for this purpose. The settings for In4 and Out1 are
disabled and fixed to 4800 Baud when SeaTalk -> NMEA translation is enabled.
Care should be taken when selecting other speeds than 4800 Baud with respect to possible queue
overflows. See paragraph ‘Data Throughput’ for more information.
Talker ID
The multiplexer allows you to change the Talker ID of incoming sentences. The Talker ID consists
of the first two characters of an NMEA sentence and determines which instrument (talker) the
sentence is originating from. Enter the desired Talker ID in the edit box of the desired input and
press the Enter to send the setting to the multiplexer. A Talker ID may consist only of upper case
characters and numbers.
When the Talker ID is changed, the background turns yellow to indicate that de modified Talker ID
has not yet been sent to the multiplexer. Pressing Enter will send all Talker ID’s to the multiplexer
and the background colour will return to white again. It is possible to change all Talker ID’s first
and press Enter after changing the last one. Starting at the Talker ID field of input 1, pressing the
Tab key will jump to the Talker ID of the next input.
Clicking the Read Configuration button will read the Talker ID settings from the multiplexer. Any
modified Talker ID’s that have not been sent to the multiplexer yet (yellow background) will revert
to their original values. To clear a Talker ID, simply clear the edit box(es) by selecting them with
the cursor and press the Del or Backspace key on your keyboard and finally press Enter. An empty
Talker ID setting will show two dashes.
With the setting as shown in the picture, any NMEA sentence received on input 3 will get Talker ID
‘WI’. A combined wind instrument may output a Talker ID of ‘II’ – meaning ‘Integrated

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Instrument’. Some navigation programs may not accept this and require ‘WI’ as Talker ID for
weather instruments. With the setting as shown, an IIMWV sentence from a wind instrument will
be changed into WIMWV. NMEA sentences received on inputs 1, 2 and 4 remain unchanged.
Setting a Talker ID can also be useful when similar instruments are connected to the multiplexer
while the navigation software must be able to distinguish between the data from these
instruments. A catamaran for instance could have a depth sounder in each hull, sending similar
sentences to the navigation software. Setting the Talker ID for two inputs to ‘H1’ and ‘H2’
respectively allows the software to recognise both depth readings separately.
Real-Time
The Real-Time option bypasses the queue for a specific channel. During normal operation, all
incoming NMEA sentences are stored in a queue - one for each channel - that can hold several
seconds of NMEA data. In situations with heavy NMEA traffic, these queues can be filled up quite
rapidly until an overflow occurs. If this is the case, the red LED on the multiplexer will blink as well
as one or more of the OF indicators at the end of each input section. The Statistics window (menu
Tools Show Statistics) will show a constant high for such a queue.
An occasional overflow does not pose an immediate problem, it only means that every now and
then an incoming NMEA sentence is discarded because there is no room left in the queue.
However, when a fluxgate or gyrocompass is connected, which sends its heading 10 or 20 times
per second, the corresponding input queue in the multiplexer is filled up constantly. Together with
NMEA data from other instruments, the total amount of data passing through the multiplexer gets
so high that this queue will be in a constant overflow situation, resulting in an unacceptable delay
of information of up to 20 seconds. This makes it impossible for an autopilot to steer on a compass
heading.
The overflow indicators (OF) at the end of each input section show which input is causing the
overflow. The indicator corresponding to the compass channel will be lit almost continuously. By
enabling the Real-Time option for the input that is connected to the gyro or fluxgate compass, the
queue of that input is bypassed and the NMEA data from the compass is passed through the
multiplexer without delay. Some NMEA sentences will be discarded when the multiplexer is
servicing another input but this is far less of a problem than having a 20 second delay in the
heading information.
See the section ‘Data Throughput’ for other ways to prevent overflow situations with different
instruments
AIS (Input 1 only)
This option enables AIS mode for input 1, in order to connect an AIS receiver or transponder to the
multiplexer. It sets the speed of In 1 to 38400 Baud and it prevents data received on In 1 to be
sent to Out 1 when the multiplexer is in Hub or Auto mode.
It is very well possible to connect an AIS receiver or transponder to any input and set that input to
38400 Baud, but this requires the multiplexer to be set to Server mode to prevent the AIS data
from being sent to Out 1, the port that is generally used to control an autopilot at 4800 Baud.
SeaTalk -> NMEA (Input 4 only)
To receive SeaTalk®data from Raymarine®instruments and convert it into NMEA sentences, this
option must be enabled. SeaTalk is a proprietary protocol developed by Raymarine and it is used
for data exchange between Raymarine navigation instruments like the ST40, ST50 and ST60
series. To be able to use these instruments with commonly available navigation programs or to
feed their data into non-Raymarine instruments, the SeaTalk data needs to be translated into
NMEA sentences. See the Technical Reference section for an overview of which SeaTalk data is
translated.
Selecting this option will automatically set In4 and Out1 to 4800 Baud and disable these controls.
NMEA Output setting
This section allows you to set the speed of both NMEA outputs Out1 and
Out2. When you change the speed of Out1, the speed of In4 will also
change. Out 1 is generally used to control an autopilot and should be
left at 4800 Baud for this purpose. The settings for Out1 and In4 are
disabled and fixed to 4800 Baud when SeaTalk -> NMEA translation is
enabled.