Flow control can be used by the FT232R, FT2232C (UART mode) and FT232BM devices to flush the buffer in the chip. Changing one of the modem status lines will do this. The modem status lines can be controlled by an external device or from the host PC itself. If an unused output line (DTR) is connected to one of the unused inputs (DSR), then if the DTR line is changed by the application program from low to high or high to low, this will cause a change on DSR and make it flush the buffer.