"Roger Long" wrote in
:

Both fixed mount and portable Garmin's show the NEMA out line from the
GPS to be connected to the ata In" in line on the radio. The radio
"Data Out" line is indicated as connecting to "Black - Neg Ground". I
therefore put a wire from the ground block where the black negative
lead from the GPS power cord attaches and ran it to the Quest radio
"Data Out" lead. I'm sure this is what it said to do but it seems
odd.



Don't ground the data lines, no matter what it says. No sense having the
Quest output IC operating into a short, which might shorten its life.
It's a happy camper operating into an open its whole life. Just insulate
the open output lead with tape. Data out of the GPS hooks to Data in on
the radio. That's all it takes.

Be informed that only ONE "talker", a device that SENDS data out on the
archaic NMEA serial bus is allowed. Up to 16 "Listeners", devices that
listen to the ONE talker, is allowed before the talker's output gets
loaded so bad the data received starts faulting. If you have more than
ONE talker on your NMEA network, you must contact Meindert at Shipmodul
to order his "multiplexer" (DID I DO IT RIGHT, Meindert??..(c. A
multiplexer has, usually, 4 input lines to hook the talkers' data outputs
to, one talker per input port only please. The multiplexer stores all
the data pouring into it in internal memory, simultaneously, from the
uncontrollable talkers, then, "services" each input port, in sequence,
reading and clearing each ports memory as it dumps what it finds into the
OUTPUT terminals of the multiplexer for all the listeners to hear, in
sequence instead of all crashed at once together. This round-robin
sequencing continues, ad nauseum, as long as the system is on. Some
multiplexers route data from the input ports through the RS-232 serial
ports to your nav software, so the computer can digest and massage the
data before it comes back out of the computer to be digested by the NMEA
listener devices. This is how the nav software, for instance, adds
waypoint data to the NMEA serial data stream the listeners get. The
computer stalls the data the multiplexer is feeding it, then injects its
data, then resumes the data stream from the multiplexer, transparently to
the listeners.

NMEA is simply a proprietary-data on an RS-422 serial bus (switches from
0=0V to 1=+5V back and forth). Older computer had RS-232C serial ports
that some could read 5V data, but RS-232C has 0=-12V and 1=+12V making it
more immune to noise that gets into the data lines, making NMEA's mostly-
ignored + and - balanced wire scheme unnecessary. NMEA chose RS-422
because they'd had to have -12V power supplies in all their +12V stuff if
they chose RS-232C. It's all moot, now, of course. The whole damned
world has gone Ethernet or USB data which is much more intellegent....

Larry
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