Using com0com and RealTerm on Windows 8 (x64) & 8.1

Every new version of Windows seems to make this harder. (See updates below for windows 8.1 x64)


Initially RealTerm displays errors when installing and running.  The fix is simply to run as administrator.  (Having administrator privileges is not sufficient.) At some point something changed though and now I no longer have to run as administrator.  I’m not sure if it’s only required on the initial install/run, or if changes I made to get com0com working also affected RealTerm.

com0com (windows 8)

Installing com0com required more effort. Initially it showed multiple errors during install. Something like:

(SetupCopyOEMInf(C:\Program Files (x86)\com0com\com0com.inf) ERROR: 0xE000022F)”.

The virtual com ports displayed in DeviceManager, but after reboot were labeled with a warning about not having digital signature verification. I tried a number of things before I got it working. In the end, I think this is all that’s required:

  1. Enable test mode per the readme.txt
    1. i.e. bcdedit.exe -set TESTSIGNING ON
    2. In windows 7 (x64), that was sufficient for me.  It seems some people also had to disable verification via that same tool, but that no longer works in Windows 8 regardless.
  2. In windows 8, you also need to A) bypass/disable driver signature verification or B) sign the com0com driver.
    1. To bypass temporarily,  you can go in to the windows 8 startup options menu and disable driver signature verification. Once disabled, com0com installed and worked fine. However, I could not figure out how to disable the verification permanently at the time, so it reverted after every reboot. The drivers would be installed, but disabled in device manager.
      1. I later did read about ways to permanently disable the driver verification. I did not try this though since signing the driver was sufficient (and would seem to be slightly more secure.)
    2. To sign the com0com.sys driver (in the “Windows/System32/Drivers” directory), I used this tool: “Driver Signature Enforcement Overrider 1.3b” at Once signed (and still in windows test mode), com0com works as it did in Windows 7 x64.

[Update 2014-06]

com0com (windows 8.1)

In windows 8.1, signing the driver as described above no longer seems to work.  However disabling driver signature verification via windows 8.1 recovery troubleshooting restart menus did allow com0com to install and function.  (I’m not sure if it will continue to function after a normal restart though.)

This entry was posted in Technical. Bookmark the permalink.