"Glen Wiley Wilson" wrote in message
news
snip

If you select a multiplexor, make
sure it has the isolation feature. I believe that Meindert's have
this.

That's right. And beware of the new 'improved' model of Noland: this one has
NO galvanic isolation.

To make it more complex, not all NMEA instruments are actually using
RS-422. For instance, my Garmin handheld actually uses RS-232 and has
a typical serial port connector, so no convertor is necessary. My
depth sounder and knotlog seem to be using some sort of hybrid. My
autopilot is an honest to gosh RS-422 interface. When you look at the
wiring instructions, if you see a +, a ground, and a signal wire, you
aren't looking at RS-422. If you see a +, a ground, a signal +, and a
signal -, you have an RS-422. Again, I would never hook an RS-422 and
an RS-232 circuit together directly. Your mileage may vary.

In general: you can connect a RS-232 output to a NMEA RS-422 input by
connecting teh TX or OUT from the RS-232 to the + or 'A' from an NMEA in,
while connecting the - or B from NMEA in to the ground of teh RS-232 output.
The other way around (RS-422 out to RS-232 in) will mosty not work.

Meindert