10 months, 2 weeks ago.

Access to USB Port with external program

I am using a LPC1768 as pulse detector (kind of like an oscilloscope). When the unit is attached using a USB cable to a USB 2.0 or USB 3.0 port (COM3) on my Laptop, the port appears to be attached to a program called , WUDFHOST.EXE'. I can not programmatically open the port since it is being used by this driver host and I get the message "COM3 does not exist" using either visual basic, C++, or Labview. I have debugged the LPC1768 program using Hyperterminal so know it is functioning properly and communicating with the terminal emulator. What does Hypererminal do internally to access the port? How do I detach the unit from the driver host so that I can communicate use the virtual USB port on the LPC1768 while the system is running?

Follow up on my Question. This appears to be a hardware with my Lenovo laptop USB Ports. I migrated the system to my Dell Desktop and the USB port for the LPC1768 appears and can be written to and read.

posted by Jeff Babis 06 Sep 2018

If you want to access the USB portal first click on universal serial bus controller and after that, you will get the list of USB ports. If anyone facing an issue with Lenovo laptop and desktop and have any query related to this then take help from this site

posted by amara johsan 26 Nov 2018
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1 Answer

10 months, 1 week ago.

Hi Jeff,

We're glad you were able to make some headway and thanks for clarifying the problem. Presumably you are using an Mbed enabled LPC1768 board - such as this one:

If so - your host computer is actually communicating to the LPC1768 through an interface chip that is responsible for handling the board programming and standard i/o. If all is good, your board will show up as a USB mass storage device and if you check your computer's Device Manager you'll see an "mbed Composite Device" under the USB area.

If you're having problems on the laptop you can see if updating the board's firmware will help:


Ralph, Team Mbed

Thanks for the update, I moved my development system to a Dell Desktop and I am able to communicate with the LPC1768 programmatically, therefore the appears to be with my Lenovo laptop USB ports and the drivers associated with them. On the Laptop, the Device Manager does show the LPC1768 as a "mbed Composite Device" but neither TeraTerm 4.1, Hyperterminal nor my program find the USB port as available for selection as an available port. It has to be a Lenovo port problem since all is well when using my Dell Desktop. Thanx

posted by Jeff Babis 07 Sep 2018

Hi Jeff,

Thanks for the additional details. If your laptop is seeing the board as a "mbed Composite Device" then hopefully your terminal programs are just not making it obvious which COM port it is being enumerated to. We didn't mention this earlier, but the board will appear as a both a mass storage device and a serial port (a COM on Windows machines). For instance my LPC1768 board shows up as COM31.

If you go back to the Device Manager and look under Ports hopefully you'll see "mbed Serial Port" with the COM port that is associated with the board. If you aren't seeing it there, what OS are you using? You might need to install a serial driver. The last paragraph of this article (also a useful read) links to one:

-Ralph, Team Mbed

posted by Ralph Fulchiero 07 Sep 2018

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