Windows recognizes Arduino but wont assign COM port

Hello all,

I am having a problem with my Windows 7 assigning a COM port to the Arduino. I have tried the sticky posts in this section and still no help. What I have done is open device manager in windows, look at COM ports (which the Arduino shows up) and see the Arduino connected. However, there is no COM port associated with the Arduino. I went into the advanced settings to give it a port number, and when I click assign to COM port 4, windows errors out on me. I plugged my Arduino into another computer and there were no problems communicating with it.

I was wondering if anyone else has gotten this error and if they can give me any advice to help solve my problem.


I was having the same symptom, but your problem might have a different cause. Here's an excerpt from a very long and boring story about what worked for me:

...the VCP drivers from FTDI (CDM 2.08.24 WHQL Certified) are nice and signed. They install successfully, and Device manager shows a new entry "ATmega16U2" under a new class "Atmel USB Devices". No yellow exclamation mark, and its properties look good.

Maybe it'll work for you...


The ATmega16U2 does not need/use FTDI drivers.

The only reason your ATmega16U2 showed up in device manager after trying to load the FTDI drivers, is that during the FTDI install, it caused Windows to re-enumerate the devices.

I suspect you had installed FLIP from Atmel before doing this and the re-enumerate caused Windows to find the Atmel DFU drivers in the FLIP package.

Thanks, Louis, that's a great explanation of why it worked. Are you referring to finding FLIP's usb/ia64/libusb0.*? I may have to go back and unintall VCP and put the 16u2 back into DFU mode to verify this. Shoot, I can erase 'em back to state they were in when I received them.

In the meantime, what should ukeri do?


I would suggest trying the IDE installer created by Eried:

Alot of people have had good results with his installer.

Holy moley!


How many people could this have helped?!? When I think of the lost hours and lost goodwill to the business, I have to shake my head.

I hope Arduino LLC clicks on that Donate button once a week for as long as he maintains it. Then they should post a link and proclaim their eternal gratitude on the official website. That's a good start anyway. :slight_smile:

Thanks for bringing this needle up out of the haystack!


Hey guys,

First, thanks for the response and update on what I have been trying. I noticed I was using arduino 1.0.3 build and there was a 1.0.4 build available. I decided to download that and use those drivers to see if it would work better. I reinstalled the arduino with the new drivers. I am still getting the message that the arduino drivers are installed correctly and the arduino is under the COM and LPT section in my device manager, but it has not been enumerated. I then downloaded the enhanced installer which Louis provided the link to (,118440.0.html) and uninstalled my device again, installed that package, and reinstalled with the enhanced drivers (I believe the drivers to be the exact same, but hey, why not use the drivers supported by it). Still the same problem as before. Device manager says everything is working fine but windows is not enumerating the arduino. The strange part is, I can communicate with it on a friend’s computer just fine. I now believe this is an error on the windows side of everything.

As for /dev’s old post, I’ve been reading through that, but its going over my head a bit. If I can’t communicate with the arduino currently, I can I communicate with it once in DFU mode? My assumption is that it would communicate via different drivers, but I am unsure. Also, I don’t have FLIP installed on this computer

I am using an arduino ethernet, not a mega. I know there are many versions of arduinos out there. However, the ethernet is basically the uno R3 with a built in etherenet shield.

Finally, I am trying to modify the LIFA (Labview Interface for Arduino) script to be communicating over ethernet instead of serial. I noticed that after I uploaded my script to the arduino, I have been getting this problem. However, I have since then plugged the arduino into another computer and it still communicates serially. I use the built in LED to signal when the pointer is in specific parts of my code. When I plug power into the arduino, the green LED goes high, then low (due to my code changing it) I don’t think this is a problem.

That all being said, I am trying to look into things on Window’s side of everything.

One more thing. When I upgraded from arduino IDE 1.0.3 to 1.0.4, I could not get windows to autorun the arduino IDE when I double clicked a .ino file. After some googling, I found out that I had to change something in the registry to point to the correct path. Basically, windows was looking for the IDE at the old 1.0.3 location instead of the new 1.0.4 location and I had to change the registry so it looked in the proper location. Do you think something in my registry may have been changed which is causing my errors?


I am using an arduino ethernet, not a mega. I know there are many versions of arduinos out there. However, the ethernet is basically the uno R3 with a built in etherenet shield.

This changes things quite a bit. The Arduino Ethernet does not have built in USB to serial.
What are you using for USB to serial to connect to the Arduino Ethernet?


Yes it does and I forgot to specify the chip. It is a USB2Serial Light adapter. The first time I got communications working, I just plugged in the adapter to the arduino and used the drivers from the arduino 1.0.3 build. I don't think I had to install anything else. This has been my standard practice for communications with this arduino and everything has worked out thus far.


Just to be clear, you have the two following products connected together:

What is the Hardware ID for the USB2Serial Light?

Go to Device Manager
Right Click USB2Serial Light
Select Properties
Select Details tab
Change Property to Hardware Ids
What is displayed under Value?


Yes and yes. Those two are connected together. I do NOT have the Ethernet PoE to be more specific.

The hardware Ids are


Under the Drivers tab, what information does it display for Driver Provider, Date, Version, etc?
What is the Device Status on the General tab?

What version of Win7, 32 bit or 64 bit? Service Pack?

Driver Provider: Arduino LLC (
Driver Date: 1/1/2013
Driver Version:
Digital Signer: Arduino LLC

Device type: Ports (COM & LPT)
Manufacturer: Arduino LLC (
Location: PORT_#0001.Hub_#0004

Windows 7 Professional, SP1.

I went into the event log and I found this error when trying to manually switch the arduino to COM4.

Faulting application name: mmc.exe, version: 6.1.7600.16385, time stamp: 0x4a5bc3f1
Faulting module name: MsPorts.dll, version: 6.1.7600.16385, time stamp: 0x4a5bc616
Exception code: 0xc0000005
Fault offset: 0x00006e87
Faulting process id: 0x12d8
Faulting application start time: 0x01ce24bc8918ccbc
Faulting application path: C:\Windows\system32\mmc.exe
Faulting module path: C:\Windows\system32\MsPorts.dll
Report Id: b53029e2-90b9-11e2-8f55-90fba6e581b8

maybe that will help. It is the latest lead I have to try and track something down.


Please attach your c:\Windows\inf\ file.
This may have some more clues to the problem you are having.

Here ya go (2.21 MB)

Can you zip it up and then attach again?

In the present format I am not able to download the whole file and each time I download it, I get a different size.

Sorry for late response, here ya go. (166 KB)

Unfortunately there is nothing about the Arduino driver installation in the log.

The last entry in the log is dated: 2010/07/06 03:07:28.846

Ya, that's what I noticed too... I was hoping it was going to be in machine time or something.

To be honest, I just took a knee and brought in a lap top to do serial monitoring for debugging purposes. I've wasted enough time on this computer to get serial communications up and running while it works perfectly fine on others. O well :frowning: