> 3.2 | Operation

> 3.2.1 | USB VCOM Port Emulation

> The virtual COM (VCOM) port emulation under Windows XP is involved with the usage of a USB serial number provided by the device: If a serial number is assigned this number identifies the USB device within the operating system. If no serial number is assigned the USB device is identified by the allocated USB port number.
> The modules have no default USB serial number and are therefore identified by their physical USB port number. This means that when the USB port of the module is detached and replugged to another USB root hub port the USB driver must be set up again for the new physical USB port. If there are several USB devices without serial number each must have a specific physical USB port number depending on the USB root hub port it is connected to.
> However, it is possible to use varying serial numbers. For more information on how to configure varying serial numbers see Section 3.1.2 and [2]. The handling of a single module becomes independent of the USB root hub port it is plugged in. The module is always assigned the same USB VCOM port and no additional explicit driver installation is necessary. For multiple modules however, each module is assigned a defined USB VCOM port. The USB VCOM port no longer depends on the physical USB root hub port the module is plugged to. It always remains the same. There is an initial explicit installation required for every new module attached to the USB host.
> It is also possible to use a fixed serial number for the modules. However, fixed serial numbers are not supported by Microsoft and therefore not recommended.