Every time you unplug and re-plug a USB serial cable you cause the system
to create a new IRQ address for it, called COM5, 6,7,8,9 etc.  If you do
the thing where you "remove usb devices safely" routine you can avoid this.
b
On Mon, Nov 19, 2018 at 12:13 PM geneb via cctalk <cctalk at classiccmp.org>
wrote:
  On Mon, 19 Nov 2018, Ethan via cctalk wrote:
 > I have a question. I use the USB port for
serial. In my program, I use 
 a
 > fixed com port. When going to the control
panel, I find that I see (in 
 use)
 > tags on some of the com ports. I'm the
only one currently using the com
> ports but recently another (in use) showed up, requiring me to modify 
 my
 > program to use another com port. How does one
unuse a com port? how do 
 I
   find out
what is using it so I can stop it? I'm using windows 7
 professional. Has anyone else had this problem? Dwight 
 Do you unplug the USB to Serial dongle with a terminal program open?
 
  FYI, "In Use" doesn't mean the port is actively used by another
process,
 it means that the /name/ has been assigned and isn't available to assign
 to a new COM device.
 g.
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