Navico MX420 Installation & Service Manual
Also see for MX420: Operator's manual
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Contents
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60MX 420 Installation and Service ManualThere are differences in the electrical interface specification between NMEA 0183version 1.5 (introduced in 1987) and NMEA 0183 version 2.0 and later (introduced in1994). Some older model equipment utilize RS-232, others use RS-422, and othersmeet the older version 1.5 specification. In an effort to simplify your interface capabili-ties, you should take the time to determine which electrical interface specification all ofthe interfaced equipment meets.NMEA Interface to other EquipmentThe MX420 meets NMEA 0183 version 2.1 electrically, and in protocol. As version 2.1is not necessarily compatible with the older version 1.5, the differences in hardwareare mentioned here to avoid possible conflicts:Listener:The listener input works with a threshold of 2 volts compared to the former 4 volt. It isstill an insulated input and, in general, there should not be any interface problemsreceiving data from the olderstandard.Talker:The talker output is a RS-422 output:NMEA talker output B is active compared to GND or shield of the navigator. In the oldversion, output B was normally tied to GND or shield.The maximum drive voltage between the talker A and B outputs is ±6 volt.Compared to the former 0 to 15 volt output, the negative voltage between the talkerA and B output may be a problem on older listeners which do not meet the newstandard.The minimum output voltage may be as low as ±2 volt. This is not compatible withthe former 4 volt input threshold and may be the cause of interface problems. If thisis the case, try using the MX420’s RS-232 interface. This may more likely solve theproblem. Otherwise third party conversion boxes may be necessary.Cables provided for the NMEA signals are shielded pairs. If extension cables areneeded, be sure to use similar shielded pair cables in order to avoid spurious signalradiation. More than one NMEA listener can be connected in parallel to the same NMEAtalker. The maximum number of listeners connected to a single talker is dependent onthe combined listener input impedance’s, and the capacity available for data through-put. |
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