Setup of the USB interface with the FTDX3000 is very simple but it can seem confusing. It is only confusing because people may not be familiar with the idea of a Virtual COM Port, which only exists inside the USB connection between the FTDX3000 and the PC.
Yeasu has done a nice job of implementing the USB interface. It is explained in their USB Driver Instructions. When you install the driver it creates 2 COM Ports. One is called “Enhanced” and is used for the normal interface for CAT communications with your PC applications. The other “Standard” Port provides an Application Interface for CW keying, PTT, and FSK keying. You can see these COM Ports in the Device Manager and tweak their settings. Here is what mine looks like after installation:
I use COM6 for the CAT interface and COM5 for CW, PTT, or FSK keying. I use N1MM as my main PC Application, and use the MMTTY RTTY software which is called from N1MM. MMTTY has the ability to interface to the Virtual COM Port using something they call EXTFSK for specifying where to get the FSK binary keying signal.
You can read all about how this works with N1MM, my favorite Contesting software, in the N1MM documentation on RTTY and MMTTY. You can also get more of the details in the MMTTY documentation.
Kg3v Ham Radio Blog 
I am at a loss with the virtual com port driver. I downloaded the zip file Yaesu recommends from Silicon Labs. But when trying to install I get an error msg that it will not work on my machine (H/P laptop 64bit running Window 10.). Laptop is only a couple yrs old so no serial port, just sub. Contacted Yaesu & the said to let Windows find the driver. Win 10 says all drivers are working. Now just chasing my tail. Would you have any ideas? Thanks for your blog,by the way!
Jerry
You need to run it as an Administrator
Jerry,
Have you had any better luck with this> I have not tried to install with WIN10 at this point, and do not have a WIN10 machine in the shack. Let me know how you are doing. Have you tried posting anything to the FTDX-3000 Groups? That would be my suggestion. I have to believe others have tried this with WIN10 by now. I would tend to NOT trust WINDOWS to find the driver. I will check the YAESU Site and see if they have something that they claim will work with WIN10. I suggest uninstalling and starting over, using whatever you can get from the YAESU Site,