Question: What is the significance of the unique serial number string option in the Full Speed USB (USBFS) Component?
The host will use the serial number string to identify the USB device internally. The serial number string can be enabled or disabled in the String Descriptor tab of the USBFS Component.
The use of the serial number string is optional. If the serial number string option is not enabled in the PSoC® Creator™ project, the descriptor file will not have a serial string in it. In this case the OS will assign its own serial string for the device based on the port where the device is connected. Consider the case of a device without a serial number string in the descriptor. When you connect the device to one of the USB ports, the OS will assign a serial number to the device. Now, if you disconnect the device and plug it into another port, the device will enumerate again, with another serial number string. This will not happen in a device with the serial number string enabled.
For the USBFS Component, you have three different options for the serial number string. If you choose User Entered Text, the user can choose the serial number string. If you choose User Call Back, the serial number string can be provided on run time by the application on the host. If you choose Silicon Generated Serial Number, the serial number string will be assigned based on the silicon ID stored in the register. This value will be different from device to device, but it is not guaranteed to be unique. Whenever you connect a device with a different serial string, the device will enumerate again.