NM-251A-MUX    
Dual Input NMEA Buffer Splitter With Multiplex Functions

  
Introduction, Operation, Input ports , Output ports, Connections, Power Supply, LED Indicators, 
Dip-switch & Jumper settings, Specifications, Printed Circuit board, Downloads, Certificates
Price ... 240.00 EURO
Intoduction
NM-251A-MUX is a two input channel multiplexer with five output channels NMEA-0183 data multiplier. It enables combining and multiplying of NM-0183 sources to all navigational instruments through five talker ports and PC connection through RS-232.
 
Operation
NM-251A-MUX acquires the NM-0183 signals from the two optically isolated inputs, combines the data and outputs them to the five general output ports and the RS-232 output. The NM-251A-MUX has three distinct functional modes that can be selected from the user via dip-switches:

  1. Mux mode: The combined output is routed to all five output ports and the RS-232 output. All outputs can be configured to transmit at 4.800/9.600/19.200 or 38.400 baud.

  2. Split/Mux mode: The combined output is routed to the fifth output and the RS-232 interface while the first input is transmitted to outputs 1&2 and the second input to outputs 3&4. Combined output only can be configured to transmit at 4.800/9.600/19.200 or 38.400 baud.

  3. Fallback mode: NM-251A-MUX acquires NMEA-0183 sentences from the most significant input and immediately sends them to the general purpose outputs and the RS-232 output. A watchdog timer routine supervises if the NMEA signals are correctly applied in the primary input and switches to the secondary input whenever there is no NMEA sentence for at least eight seconds. In this case the secondary input starts receiving data if there is an instrument attached. If not, the device automatically returns to the primary input after eight seconds. When the secondary input is already in receiving mode and an NMEA signal is applied to the primary port, the device immediately switches to the primary input. In the case that no signal is applied to any input, the device “circles” around sampling the two listener ports every eight seconds until an NMEA-0183 signal appears to any of the two listener ports.


The NM-251A-MUX has also the following features:

  1. Configurable output transmission speed: The output speed for the combined data stream is user selectable via dip-switches and can be set to 4.800/9.600/19.200 or 38.400 baud.

  2. Input Autosense: The NM-251A-MUX senses a correct NMEA signal application to any of the two inputs while in mux or split/mux mode. The LED Ina and Inb flash at 1/2 Hz while no NMEA signal is applied or the polarity is wrong. If at least one signal is correctly connected to one of the inputs it starts functioning normally.

  3. Data overflow indications: The NM-251A-MUX has different overflow indication for each input. When an overflow occurs some of the input data are not transmitted. This is normal when connecting to instruments transmitting great amount of data, and can be resolved if the output transmission speed is increased.

  4. Watchdog: The integrated watchdog reset feature will bring NM-251A-MUX back from any unresponsive state into normal operation.

Input ports
The NM-251A-MUX has two input ports that can be connected to any instrument intended for marine use that can output NMEA-0183 signals. Each one of the two listener ports is optoisolated as specified in NMEA-0183 protocol, thus data(-) pole should never be connected to NM-251A-MUX ground. If the instrument’s talker port is single ended, connect that terminal to the Ina(+) or Inb(+) input and tide the Ina(-) or Inb(-) to instrument’s ground. If an RS-232 signal level is connected the ground pole (GND) should be connected to Ina(+) or Inb(+) and the data pole (TXD) to Ina(-) or Inb(-) respectively. The two listener ports can acquire NMEA sentences carried in TTL, RS-232 and RS-485/422 signal levels.

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