Changing Serial ports from COMX to COMY using WMI

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kobos posted on 07-01-2011 10:56 AM

Scenario: I have a thermal printer connected to a serial port currently assigned the number of COM1, I need to change this port number to say COM55. Now this has to be done silently (ie in code or script), if i had the luxury of just going through device manager i would but that isn't possible as this has to be part of an installer. The terminal services command "Change Port COM1=COM55" relies on group policy settings being correct and is reset when the computer shuts down. And so my only real option without trawling the registry and changing each corresponding key - some of which are dependent on the driver manufacturer - is to use WMI.

#change the qualifiers for "DeviceID" to supposedly allow you to write to it

$writeableProperties = Get-WmiObject -List -Recurse Win32_SerialPort |
    select -Expand Properties | Where-Object { $_.Name -eq 'DeviceID' }


#Pull out the SerialPort
$SP = Get-WMIobject Win32_SerialPort | Where-Object { $_.DeviceID -eq 'COM1' }

#change the Device ID
$SP.DeviceID = "COM55"

This doesn't work as intended, ie it changes the deviceid but that doesn't propagate further, i'm therefore under the impression that there is a parent object to this that determines the port number. I'm fully aware of how bad this all is, but i have little choice.

any help would be greatly appreciated.


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Microsoft MVP
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You won't be able to set the id in this way.  The DeviceId property is read only.  See

Its also the key for the class which makes it even harder to change as it is the property used to uniquely identify the port

I'll see if I can research a method for you

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Yea, this is all hackety-hack at the moment. Any help would be greatly appreciated,  I am considering hooking MMC and seeing what the Change ports button actually does.

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I hooked MMC in the end and crafted(hacked) a solution in C++/Win32, i need to generalize it and tidy up some of the more dangerous aspects but i'll try to post a code sample in the coming days that works smoothly.

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