There are three layers of operation happening when a device is interacting with a host controller: the functional layer, USB device layer, and the USB bus layer. On the Host side, the functional layer of PC applications sends data to or from the device. For example, an RS232 terminal application, like HyperTerminal, forms the USB functional layer which displays the data received or transmits data to the USB device. The HyperTerminal application may use standard Win32 COM APIs which, in conjunction with a USB device driver, will logically convert that data back and forth from USB packets.