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NMEA Combiner / Multiplexer
Model AISC



This model Brookhouse multiplexer was originally designed for integration of  the popular Raymarine C- and E-series  chart plotters, now called the "classic" C/E series.  The new "wide screen" C/E series offer extended NMEA 0183 integration possibilities and do not require a multiplexer, unless one or more of the special Brookhouse mux features are required, such as NMEA conversion to adapt to existing equipment.

In the following description please read any reference to Raymarine C/E series as "classic C/E series".

No other multiplexer or interface available today offers the same degree of integration of C/E-series displays with other instruments. It allows simultaneous connection of an AIS receiver or transponder, fast heading sensor, DSC radio and other NMEA-compatible marine instruments to the single NMEA input port of the C/E-series display. In addition, this multiplexer model accepts the NMEA output of the C-series and performs baudrate conversion as well as NMEA protocol conversion, if necessary, to enable connection of NMEA listeners such as an auto pilot, DSC radio etc. Installation of this multiplexer model is simple, no setup or configuration is necessary, unless special features are required.

The Brookhouse AIS-C multiplexer has 4 opto-isolated NMEA input ports, 2 NMEA (RS422) output ports, one RS232 output, one RS232 input, optional USB.

For quite some time the standard model Brookhouse NMEA multiplexer has already been the favorite choice for connecting multiple NMEA compatible instruments, including AIS, to Raymarine  C/E-series displays. Based on the experience with typical installations and some issues surrounding C/E-series compatibility with other instruments, this new model NMEA multiplexer was developed to take seamless integration a step further.


For the connection of an AIS receiver or transponder to the C/E-series NMEA input port, it has to be configured for high-speed communication at 38400bps. The C/E series plotters also accept other NMEA data via the 38400 bps AIS data stream, therefore the connection of a multiplexer to this port is possible.

Before multiplexer model AIS-C was available, the standard Brookhouse multiplexer was already suitable for combined input of high speed AIS and other (standard 4800 bps) NMEA instrument data. By setting the configurable standard mux' 5th input port to 38400, this port can be used for AIS. The multiplexer's combined output data stream is transmited to the C/E series NMEA port at 38400 bps.

This application of the standard multiplexer with 5th inpt port has found many satisfied users.

However, configuring NMEA for AIS on the C/E-series has the side-effect that the NMEA output is also set to 38400 bps, which is unusable as input to other standard 4800 bps NMEA listeners.

Brookhouse multiplexer model AISC offers a solution for this problem. Read about it below.

Baudrate conversion

Setting the baud rate of the NMEA input port of the C-series to 38400 for AIS, also affects the NMEA output port baudrate, which is set to 38400 at the same time. This high baudrate makes it impossible to directly connect instruments with standard 4800 baud NMEA input ports. The problem has been resolved by adding baudrate-conversion to the Brookhouse multiplexer. The C-series 38400 baud output can now be connected to a 38400baud NMEA input port on the multiplexer and the data stream is available at 4800 baud on another NMEA output port . Multiple standard NMEA listeners can be connected to this port. The speed-conversion is a separate, independent function in the multiplexer.

Configurable 4800 bps NMEA output

The above explains how the baudrate of the combined output data stream of multiplexer model AISC is 38400 and that return data from the C/E series is converted back to 4800. However, it is often important to be able to output data from one or more of the standard NMEA inputs at 4800 bps as well. Three configurable modes are available:

  1. The 4800 mux output consists exclusively of NMEA data received from the C/E-series. (baudrate conversion output)
  2. If the multiplexer detects that no data is being received from the C/E-series, it outputs data received from selected inputs.
  3. Data from selected inputs is always output, combined with return data from the C/E-series.  

The above is described in detail, with diagrams,  on the page "baudrate conversion" under Multiplexer features. Mode 2 is also described under "data stream switching".

Auto pilot NMEA compatibility

The features of the Raymarine C-series products have made it an attractive option for installation on boats with existing instruments and (non-Raymarine) auto pilots. The C/E-series output NMEA version 3.01 auto pilot control data (APB sentence). However, the NMEA version accepted by many auto pilots is 2.1 or older. The result is that the newer data-format is not recognised and these auto pilots do not function with the C-series equipment. Therefore baudrate-conversion is not always enough to drive standard NMEA auto pilots from the C-series. The Brookhouse multiplexer model AIS-C has a unique feature that adapts the NMEA data from the C-series to a format recognised by the auto pilot, if required. The script to perform the conversion is available to all users at no charge. Loading the script in the multiplexer is an uncomplicated procedure.

 Other NMEA compatibility

Seatalk instrument and GPS data on the Seatalk-bus is converted to NMEA by the C/E-series and is also available via the NMEA out port. This data can be used to feed a DSC radio, repeater instruments, etc. Potentially NMEA compatibility problems may surface here as well. Again, these problems can be ironed out in an elegant way by the Brookhouse multiplexer. Many existing scripts are available from Brookhouse that can be loaded into the multiplexer in a simple way by the user, to perform conversions and adaptions of the data. Redundant NMEA data can be filtered out, if necessary. For the more technically oriented users, details are available in the Brookhouse document "NMEA data manipulation and filtering”

Fast heading sensor

Raymarine recommend using a fast heading sensor to improve the performance of Marpa and for chart radar overlay. Connection to the C-series display is via the NMEA port. The refresh-rate of heading data is usually  10Hz. This means that 10 NMEA sentences with heading data per second are transmitted. Combining this high intensity data stream with AIS and other NMEA equipment via the Brookhouse multiplexer presents no problems.



The majority of C/E-series display installations use a Seatalk GPS receiver. Users are increasingly aware of the dependancy on this single GPS. It is often mounted in a vulnerable position where it can easily receive physical damage. The prudent skipper will install a spare NMEA GPS as backup, preferably below-decks. The Brookhouse NMEA multiplexer provides enough input ports to connect this extra GPS together with AIS and other NMEA talkers to the C/E-series display.

Installations without AIS

For C-series installations without AIS, but with a fast heading sensor, the high baudrate setting of 38400 is still preferable, as this ensures sufficient bandwidth for the data intensive heading sensor plus other NMEA talkers. The Brookhouse multiplexer model AIS-C is still the recommended choice in this case, because of the baudrate-conversion and other features.


As a chart plotter, the C-series offer all navigation options that one can desire. However, the display is often mounted outside at the steering position and on many boats we find a (laptop) computer at the navstation below-decks, which can be used as a back-up, for route planning, tracking etc. The Brookhouse NMEA multiplexer AIS-C has a RS232 port for output of the combined data stream to a computer. A USB port is available as an option.

Other applications

Brookhouse multiplexer model AISC  is also suitable for  non-Raymarine installations. Many other manufacturers' chart plotters have similar features (and limitations) as the C/E-series, and model AISC will provide a good solution for integration of this equipment as well. Model AISC is equally suitable for installations with a computer only.

Other features and optional extras.

All standard features described under "Multiplexer features" are included for model AISC and all optional extras are available.


  • 4 opto-isolated  NMEA Listener (input) ports.

  • 1 output RS232 port..

  • 1 intput RS232 port

  • 2 output RS422 ports (differential NMEA talker port)

  • baudrates:  3 input ports @ standard  4800 bps (standard NMEA), 1 input port @ 38400 bps.
    RS232 Output port: 4800/9600/19200/38400 bps configurable in setup mode, default 38400 bps.

  • baudrate conversion: 38400-4800 bps

  • Indicators: red LED for power, green LED for data-transmission.

  • Supply Voltage: DC 9-35 Volts.

  • Reversed polarity protection.

  • Power Consumption: 45 mAmps. @ 12V (with all ports active)

  • Physical size: 110x65x37mm (hxwxd)

  • Weight: 120 grams

  • Mounting: bulkhead mounting with screws.

  • NMEA  management and control:

    • NMEA Sentence Filtering

    • NMEA Sentence editing “on the fly”

    • Automatic port switching (mainly for GPS backup)

    • Data pacing.

    • Script-driven data-stream switching.

  • Options:

    • Raymarine Seatalk support

    • USB computer connection

    • User programmable LCD


Pricing, ordering and payment 



Note: Seatalk is a trade-mark of RayMarine.