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Virtual Com Port Loopback runs w/o debugger not w/ debugger

Question asked by stearns.steve on Sep 26, 2013
Latest reply on Dec 4, 2013 by Clive One

I've brought up the ST example VirtualComPort_Loopback (V4.0.0) on a Keil demo board (MCBSTM32E vers3) and the Keil enviroment (uVision connecting through the ST virtual comport driver (  and it works fine when not run from within the debugger.  When run from within the debugger, however, the terminal emulator (PuTTY) error's out with: "Unable to open connection to Com46, Unable to configure serial port".  The Com port (46) does show up in device manager and no errors are indicated.

My uneducated guess is that the ST virtual comport driver is not happy something that's different in it's interaction over the USB connection when the debugger is running and it's refusing the terminal emulators connection.

I would really appreciate any ideas for chasing this problem down as the problem also exists on a custom board with a complex application in need of enhancing and debugging...

Thanks in advance.