GPSrChive Discussion Forum

GPSrChive wrote: Fri Jan 24, 2025 10:31 pm Just rechecked some screen captures from previous firmware versions and they have been inconsistent. Most MTP Garmin Devices only have two options for USB Interface: 'Garmin' and 'MTP'. Probably Garmin will change this again, just to keep us guessing! I am not aware of any USB-C NMEA adapter cables, so why would this option be available?

The NMEA cable is mini USB, Garmin advises a conversion cable for devices with micro USB here.
The same should be possible with a proper USB-C - mini USB conversion cable...

GPSrChive wrote: Fri Jan 24, 2025 10:31 pm I am not aware of any USB-C NMEA adapter cables, so why would this option be available?

Adapter cables USB-C for Nmea data transmission exist, they are intended for devices that have
previously used the RS-232 port. Devices equipped with a USB-C port do not require an adapter.

Przekątny wrote: Sun Jan 26, 2025 6:17 pm

GPSrChive wrote: Fri Jan 24, 2025 10:31 pm I am not aware of any USB-C NMEA adapter cables, so why would this option be available?

Adapter cables USB-C for Nmea data transmission exist, they are intended for devices that have
previously used the RS-232 port. Devices equipped with a USB-C port do not require an adapter.

Like this USB-C NMEA cable?

Unfortunately, cables like these require special drivers to be loaded before it can be used, making it highly unlikely to work out of the box with any Garmin device.

If anyone finds a cable that does work, please let us know!

I tink you really need the one from Garmin, coupled with a pass-trough cable/adapter.
Maybe this one from Garmin, but I'm not sure it is a proper pass-trough adapter.

GPSrChive wrote: Mon Jan 27, 2025 12:04 pm

Like this USB-C NMEA cable?

Unfortunately, cables like these require special drivers to be loaded before it can be used, making it highly unlikely to work out of the box with any Garmin device.

For receiving data Nmea from the device via the UBS - C port
you need software that will receive the data, not an adapter cable, if the second device has a USB.
Transmission of navigation data from the device to the computer can be done via the Nmea protocol if the software has implemented this protocol.

The adapter cable indicated in the link works, works as intended and no additional driver is needed.

Przekątny wrote: Mon Jan 27, 2025 2:29 pm The adapter cable indicated in the link works, works as intended and no additional driver is needed.

You have tested with a Montana 710 / 710i / 760i to verify?

GPSrChive wrote: Mon Jan 27, 2025 2:52 pm You have tested with a Montana 710 / 710i / 760i to verify?

The adapter is suitable for sending navigation data via the Nmea protocol from marine devices to computers with a USB - C port

Przekątny wrote: Mon Jan 27, 2025 3:27 pm

GPSrChive wrote: Mon Jan 27, 2025 2:52 pm You have tested with a Montana 710 / 710i / 760i to verify?

The adapter is suitable for sending navigation data via the Nmea protocol from marine devices to computers with a USB - C port

You did not answer the question!

Przekątny wrote: Mon Jan 27, 2025 3:27 pm The adapter is suitable for sending navigation data via the Nmea protocol from marine devices to computers with a USB - C port

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...

Something special happens with the serial cable from Garmin, the devices that support it handles serial communication directly via the pins in the USB connector, so there is no serial <-> USB conversion. The Garmin cable does change the voltage levels though to get a proper serial output.
So, if a USB-C <-> mini USB adapter connects the pins Vbus, GND, D+ and D- directly, it should work...