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[aprssig] advice on purchesing GPS for use with D-710

Allen, Richard Richard.Allen at garmin.com
Mon Aug 29 14:15:02 UTC 2011

Montana: has NMEA hidden in the USB connector with https://buy.garmin.com/shop/shop.do?pID=26668, or use https://buy.garmin.com/shop/shop.do?pID=89575 if you want to attach it somewhere. I have this on a motorcycle but haven't run the wires to my TH-D7A yet.

Oregon: has NMEA hidden in the USB connector with https://buy.garmin.com/shop/shop.do?pID=26668 or https://buy.garmin.com/shop/shop.do?pID=1169

GPSMap62: has NMEA hidden in the USB connector with https://buy.garmin.com/shop/shop.do?pID=26668

GPSMap78: has a big round NMEA serial port, here's the pigtail https://buy.garmin.com/shop/shop.do?pID=519

All of the above units will receive NMEA waypoints and plot them on the map, and there are probably a few more.


From: aprssig-bounces at tapr.org [mailto:aprssig-bounces at tapr.org] On Behalf Of Stephen H. Smith
Sent: Sunday, August 28, 2011 8:43 PM
To: russo at bogodyn.org; TAPR APRS Mailing List
Subject: Re: [aprssig] advice on purchesing GPS for use with D-710

On 8/28/2011 4:52 PM, Tom Russo wrote:
There is no mention of a classic RS-232 serial port (required to connect to a Kenwood), nor any mention of FMI support (that allows the USB interface to "morph" into a serial port when a special cable is attached).

FMI and "morph to serial" are separate things.

The FMI interface IS serial, but with a screwball proprietary binary data format rather than vanilla NMEA ASCII.

Several of the handheld usb-only Garmin GPS units will indeed "morph to serial

NMEA" with just the right cable, even though they don't talk FMI.  If you look

at the Montana's spec  says its interface is "USB and NEMA 0183 compatible,"

One can have NMEA-0183-format ASCII data over USB rather than serial -- many USB faceless hockeypuck GPSs do exactly this .    This is what I assumed they meant in the Montana description.

and on its "accessories" page there is a USB "Serial Data/Power" cable


with bare wires to access the serial data.  This cable is compatible with

several of the devices other than the Montana, including the Colorado, Oregon,

and GPSMAP 62 series.

I believe that the way these devices work (Scott Miller can correct me here

if I'm mistaken) is that they detect a certain resistance in the cable between

certain pins, and switch from USB to plain RS232 serial protocol on the data


This is how the USB-to-FMI-serial interface morphing works also.   It looks as through the complexity of the Garmin USB interfaces has just doubled,  with the magic USB-data-line pullup cable on some devices waking up FMI  while the pullup wakes up generic NMEA serial on others.


Stephen H. Smith    wa8lmf (at) aol.com
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