Re: Usbser.sys CDC Virtual COM Port

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Just to follow this up...

We have here a third party USB->8-port expander device, ie. provides 8
RS-232 COM ports on a single USB connection to the pc. This manages the
problem of dissapearing virtual COM ports very effectively.

I can connect a Win32 App to one of the virtual COM ports, see it work,
completely unplug the expander device from the USB (not just at the COM port)
and see that the app can no longer communicate with the device. After
plugging the USB device back in to the PC the software app is able to
communicate with the device as before without any need to re-start or
re-create the COM port in windows.

When disconnected the virtual com ports do disapear from device manager,
however. So it must be that the windows logical side of that device is able
to re-attach to the COM port when it comes back after being re-connected.

The device is of course using it's own custom driver not the usbser.sys but
I just thought it might be of interest that it appears perfectly possible to
maintain the virtual COM port in windows even though the device has been
removed from the USB bus.

Greg.
.

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