Montana 7x0 USB-C NMEA Cable

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Thats right, but the issue here is to connect the Montana to NMEA devices such as an autopilot on a ship using the USB-C port. You cannot use this cable for that...

We don't know if Montana will work with marine devices equipped with an RS 232 port.
The adapter has bidirectional data transmission and Montana has Nmea data transmission, so it may work.

[javawa]

No, it won't because the Garmin devices uses the USB interface in a very special way. Your cable does not support that (if it did, it couldn't be used on a computer).

[epv]

The 7x0 appears to switch USB endpoint modes - when they're not in mass storage or MTP mode they present a serial device (ACM i think) endpoint to the computer as if a USB-serial device was connected; in "Garmin Spanner" mode this serial interface at least allows software like Express to identify the device's model and serial number, but not to transfer data.

There's probably some undocumented way to tell it to send NMEA sentences too but I haven't found a way yet. This thread is the first I've seen claiming that the interface on the 7x0 series can be electrically switched to plain non-USB serial data, though. It would be interesting to know if that's actually the case.

[javawa]

According to the manual the Montana 710/760 has the following interface settings: Garmin Spanner, Garmin, NMEA In/Out, Text Out and MTP

"MTP" is the mode you normally use when you connect it to your computer.

"Garmin" uses a proprietary protocol, you need the Garmin USB drivers for that.

"Garmin Spanner" lets you choose between MTP and Garmin, and if you select this option in the settings you have to set several NMEA options (at least, that's how it works on older devices). Regardless those options, the device still uses the same Garmin proprietary protocol (when not using MTP), not serial NMEA! So why do you have to set these NMEA options? Garmin made PC software named Garmin Spanner. This software creates a virtual COM port on your PC that sends out NMEA 0183, and it uses the options that you can set on the device when you select the Garmin Spanner mode.
There is a minor problem though, the Garmin Spanner software doesn't run on computers with Windows Vista or newer...

Then there is the interface setting "NMEA In/Out", this one sends real serial data where you need that special Serial Data cable from Garmin (with a mini USB plug, not a USB-C plug...). It doesn't work with a regular USB cable.

"Text Out" sends also serial data using the special cable, using simple ASCII instead of NMEA 0183 (it sends time, position and velocity).

[javawa]

Actually, every Montana has a serial output and Garmin sells a serial cable for it...
Not separate, but integrated in the AMPS mount.

[scotte]

Just to throw some more fun into this thread while we're at it - NMEA 0183 is technically not single ended RS-232 but differential RS-422. That they can interoperate at all is arguably as much luck as it is design, and many manufacturers of consumer products muddle this by using RS-232 yet claim NMEA-0183 spec. :⁠-⁠) and/or :⁠-⁠\

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Maybe there is more confusion, not only other manufacturers, but Garmin used the term RS-232 in the instructions.


"Interfaces: NMEA 0183, RTCM 104 (for DGPS corrections) and
RS-232 for PC interface"

Unless in older devices RS 232 was actually used.

[Przekątny]

Then there is the interface setting "NMEA In/Out", this one sends real serial data where you need that special Serial Data cable from Garmin (with a mini USB plug, not a USB-C plug...). It doesn't work with a regular USB cable.

he operation of the navigation data transmission via the USB port (with x connector) depends on how you want to use it, if you want to obtain navigation data (position) in a PC with a USB port (with x connector), you do not need a special cable, a regular cable is enough.

I wrote earlier, to transmit navigation data to a PC with a regular USB cable, you need the appropriate software with which you probably agree, writing about Garmin Spanner.

It is different if we want to send navigation data from the device to a device that has a communication port other than USB.

Garmin Spanner PC did not work with newer Windows systems, but the navigation software on the PC has implemented PVT (maybe this abbreviation means Position, Speed, Time) the GPS signal from the device is read in these programs when the NMEA In/Out interface is set.

There are also navigation programs for PC using only Nmea data, we can obtain navigation data by setting the Interface Nmea in/Out in the device.

[javawa]

When you connect a Garmin device to your computer using a regular USB cable, it will never transmit NMEA data. On every interface mode it will start in USB mass storage mode (or MTP mode), except for the mode "Garmin Spanner". In that mode it will use mass storage/MTP or the Garmin protocol, depending on your choice. So if you want NMEA, you will need a program on your computer that translates the data that is sent using the Garmin protocol to NMEA messages.

The discussion about USB-C NMEA cables is less relevant though, because the Montana has a serial interface and Garmin sells cables for that. There is no need for a USB-C NMEA cable...

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Spoiler

Nmea.jpg

With the settings as in the picture and the Nmea In/Out interface enabled, navigation data is transmitted.

Information about NMEA 0183 Compatible Cable for Outdoor and Marine Handhelds:
"NMEA 0183 Compatible Cable for Outdoor and Marine Handhelds
Some Garmin Outdoor and Marine handhelds have the ability to output NMEA 0183 data to interface with marine equipment."