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How to clear or reset COM ports?

What is COM Port?

COM port (Communication port) is the name for the port serial interface that can be found in a common computer(IBM compatible). Sometimes computers come with one or two physical COM ports (RS-232), while today's models don't have them ususally. However, the COM port does not necessarily refer to physical ports, but also virtual. Such ports are created when using USB-to-UART adapter, most notably used by FTDI and Croduino. Here are a few examples of such devices: USB modems, cell phones, RFID readers, card readers, and so on.

Every time Windows register such a device with a new ID, it gives that device a new COM port (COM2, COM3, COM4, ​​etc.). Even when you turn off the device, the COM port that is assigned to the device remains reserved for it. That is, each time you reconnect they will be assigned to the same COM port. Generally it's great. The problem can occur if some software that comes into your device is set so that it can access only, say, the first five COM ports. However, this tutorial will describe how to "clean" COM ports that are in use, and how to disable numbering of new ports.

How to reset COM ports?

1. Click Start - write regedit then click Enter.
2. Navigate through folders: HKEY_LOCAL_MACHINE\SYSTEM\CurrentConstrolSet\Control\COM Name Arbiter
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3. Double-click right click ComDB on right panel
4. This will open a window with addresses ports. To reset, enter all zeros, as shown below:
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Once you confirm the changes by clicking on OK, our ports are reset. We can also check:

1. Click Start - write devmgmt.msc or simply Device manager, then click Enter.
2. From the middle pane, expand Ports (COM & LPT), right-click on any of the available ports and Properties
3. Choose Port Settings and click Advanced
4. Click on the drop down menu COM Port Number, and we see that all COM ports available.
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Check those ports after Windows assignes them a COM port, there should be written "in-use".

How to disable adding new COM port numbers?

As the title says, follow the instructions to disable the Windows computer from getting the new COM port number each time a new USB-to-UART device is connected.

1. Click Start - write regedit then click Enter.
2. Navigate through folders: HKEY_LOCAL_MACHINE\SYSTEM\CurrentConstrolSet\Control\usbflags
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3. Right click on folder usbflags, zatim New - Binary Value
4. Name the new file as IgnoreHWSerNum04036001.
5. Repeat step 3., and name new file as IgnoreHWSerNum04036010. Now in the right panel you can see:
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6. It is necessary to change the value of both files. For each individual double click and enter the value of 01:
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For more information about the advanced settings of virtual COM look here in the official FTDI document

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