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post #5 of Old 03-02-2010
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ST60 Multi NMEA -vs- RS232

I agree almost 100% , ActiSense, but would like to clarify that my comment applied specifically to the NMEA output of the Raymarine ST60 Multi.

The Multi has a 12V current-limited source on NMEA+, spec'd at 11.2 V (on 12V in) at 80 mA, and actually drives its NMEA- output via an optoisolator to ground.
The test procedure calls for a 1k resistor between NMEA+ and NMEA- and looking for data pulses on the NMEA- line. I haven't tried, but logically (pun intended) that would produce inverted RS-232 (which would be closer to MIL-188, if I recall correctly).

In the case of this particular Instrument, using NMEA+ and Ground would produce a steady "spacing" condition on RS-232. Given the >5v swing, using NMEA+ and NMEA- always worked ok for me with an *ungrounded* laptop, and of course is fine via a MUX with a "real" NMEA input, which is the better way to go. I did not have the internal instrument schematic when I first did the hookup.

Last edited by redline; 03-02-2010 at 03:42 PM.
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