Navico MX420, Инструкция по установке и обслуживанию

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MX 420 Installation and Service Manual
There are differences in the electrical interface specification between NMEA 0183
version 1.5 (introduced in 1987) and NMEA 0183 version 2.0 and later (introduced in
1994). Some older model equipment utilize RS-232, others use RS-422, and others
meet 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 of
the interfaced equipment meets.
NMEA Interface to other Equipment
The MX420 meets NMEA 0183 version 2.1 electrically, and in protocol. As version 2.1
is not necessarily compatible with the older version 1.5, the differences in hardware
are mentioned here to avoid possible conflicts:
Listener:
The listener input works with a threshold of 2 volts compared to the former 4 volt. It is
still an insulated input and, in general, there should not be any interface problems
receiving data from the older
standard.
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 old
version, 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 talker
A and B output may be a problem on older listeners which do not meet the new
standard
.
The minimum output voltage may be as low as ±2 volt. This is not compatible with
the former 4 volt input threshold and may be the cause of interface problem s. If this
is the case, try using the MX420’s RS-232 interface. This may more likely solve the
problem. Otherwise third party conversion boxes may be necessary.
Cables provided for the NMEA signals are shielded pairs. If extension cables are
needed, be sure to use similar shielded pair cables in order to avoid spurious signal
radiation. More than one NMEA listener can be connected in parallel to the same NMEA
talker. The maximum number of listeners connected to a single talker is dependent on
the combined listener input impedance’s, and the capacity available for data through-
put.