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On 15 Sep 2003 21:52:35 GMT, (NIFFOCBT) wrote:

The seatalk had no radar or chart plotter connected to it. The vessel has a
furuno Black Box 2105 radar and a Nobeltec VNS 7.0 chart plotting system
feeding only output NMEA to A/P. The reason the captain hooked all the
instruments to one port was that they were connected to separate ports and the
port that had the Control head blew out. Underway in rough seas he got in
there to "make it work" and hooked it all to one port. This worked for a few

I'm still seriously confused on how you "blow out", to use your words,
any NMEA ports, in or out, with 12 volts.....

Any serial port source has serious impedance in series with it. If
you short it to ground, no harm is done I've ever seen. The internal
resistance built into the devices protects it. If you hook it to
+12VDC, same effect. I suppose you could "blow out" one if you
plugged it into the AC genset or 48VDC if you really tried hard.

Overloading a serial port simply results in low output VOLTAGE due to
its current limiting impedance and it simply "doesn't work" because
the source output isn't high enough to switch the loads looking for
higher 1's voltages.

Hell, if they "blew out" from being shorted to something half the
boats I've worked on would be blown all to hell! It's just not
so.....

PS - If you're using an RS-232C serial port TX for a NMEA source, the
limit is about 15 milliamps of output current, which isn't many
loads.....dammit all.....(c;

Larry W4CSC

3600 planes with transponders are burning 8-10 million
gallons of kerosene per hour over the USA. R-12 car air
conditioners are responsible for the ozone hole, right?

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