Once the device has answered the first host requests with the default device address 0, the host assigns a new address to the device. The host controller has to send a USB reset to the device and to send a SET_ADDRESS (addr) SETUP request with the new address to be used by the device. Once this SETUP transaction is over, the user writes the new address into the USB Host Address for Pipe x field in the USB Host Device Address register (HSTADDR.HSTADDRPx). All the following requests on all pipes are then performed using this new address.
When the host controller sends a USB reset, the HSTADDRPx field is reset by hardware and the following host requests are performed using the default device address 0.