Windows 7 PC - disable sending data to com ports at bootup

Question

We have a Windows 7 pc connected via com 1 to a scale head. Windows 7 outputs data at boot up to the com port and scambles the scale head's configuration which has to be re-configured. We have disabled Serial Mouse Detection in the registry. When testing the com 1 port to a laptop running Hyper Terminal, we can see characters output to the screen. How do we disable all output at boot time to a com port?

Answer 1

The likeliest cause of output on the serial port at boot time is that boot-time kernel debugging, which communicates with the debugger UI on a serial console, is enabled.

You can use BCDEdit to ensure that boot-time debugging is disabled. You'll need to run the tool from an administrator-level (elevated) command prompt; to obtain one:

• Click the Start button, or press the Windows key, to show the Start menu.
• Type 'cmd'; in the search results list, you should see 'cmd.exe'.
• Right-click the 'cmd.exe' and choose "Run as administrator".
• Acknowledge the UAC prompt, entering an administrator password if necessary.

The resulting command prompt will run with administrative privilege, which is necessary to use BCDEdit. Assuming there is only one boot entry, run the following from an elevated command prompt:

bcdedit /debug off

If more than one boot entry exists, first run

bcdedit /enum

to list the boot entries and their IDs, then do

bcdedit /debug <id> off

to disable boot-time debugging on the boot entry you're using. (If uncertain, just disable it on all of them.)