I just designed a board using the MCP2221A USB-to-USART bridge device from Microchip. My development platform is currently on Windows 10. I have downloaded all of the files and utility programs I could find from the Microchip website. I also downloaded the file set MCP2221 Windows Driver 2014-10-09 and installed it. The driver install package ran without problems, so the driver install appeared to work.

Next I used the MCP2221 utility program to attempt to read the chip device and possibly program it. This is where Windows 10 appears to fight the device and driver. When plugging my PCB board into my PC Win10 gives me the following popup error:

enter image description here

Apparently Win10 will not allow the driver to proceed because the blank MCP2221 device does not have any VID or PID information in it. That is the reason I was using the MCP2221 Utility--to initialize the PID and VID and maybe other items. Below shows the Device Manager listing...

enter image description here

...showing that the device descriptor failed. The whole point in using the MCP2221 Utility is to setup this information.

Microchip's Web Forums were no help at all. All comments pertained to WinXP and Win7. No drivers, app notes, or other support items have been upgraded since 2014.

Has anyone encountered this problem with Win10 and devised a work around?

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    \$\begingroup\$ The MCP2221A comes with factory defaults VID=04D8 and PID=00DD, it is not "blank", unless you somehow zeroed the chip setting map in internal flash. If the OS reports "Device Descriptor Request Failed", it means that your device went dead, it did return NOTHING, protocol error. This is independent of OS. \$\endgroup\$ Sep 16, 2017 at 20:54
  • \$\begingroup\$ Thanks Ali for the info on the PID/VID. Chip dead? The chip is a hand-soldered SOIC so there is that possibility. Also all lines including the GPIOs were soldered in. I will solder up another board with minimum leads (Tx, Rx, D+, D-, and 3.3V power) and try again. . \$\endgroup\$
    – Doug12745
    Sep 17, 2017 at 22:17
  • \$\begingroup\$ I've seen some questions about the MCP2221A when after programming new flash values the chip would fail to enumerate the HID section after power cycling. I believe it was on MCHP forum, and there were no answers to it. \$\endgroup\$ Sep 18, 2017 at 0:36
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    \$\begingroup\$ I heard that the MCP2221A is actually a firmware product in a code-protected PIC16 device. \$\endgroup\$
    – Doug12745
    Sep 18, 2017 at 0:53
  • \$\begingroup\$ Yes it is, blog.zakkemble.co.uk/mcp2221-hid-library/#comment-206104 \$\endgroup\$ Sep 18, 2017 at 0:55

1 Answer 1


I would start by installing the latest MLA

It may be an issue with driver signing which Windows 10 seems to be notorious for.

  • \$\begingroup\$ Bilal, Downloaded the latest MLA set. I am not familiar with using MLA's but they look interesting. I did compile and install the USB Windows driver that was included, but did not see any difference--error still appears. \$\endgroup\$
    – Doug12745
    Sep 17, 2017 at 22:19
  • \$\begingroup\$ MLA is an SDK which has pre-made examples and is as simple as dropping the hex file on to the chip and loading up the provided software application. They are usually located in C:/Microchip I believe (can't confirm as I'm on Linux). This would be a good way to see if your board is at least working correctly. I've encountered this problem before on a PIC which was due to a problem with the firmware. \$\endgroup\$
    – Bilal
    Sep 18, 2017 at 2:15

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