The universal serial bus (USB) interface is used as a standard type of interface in many different kinds of devices for the transmission of data. The **data** transfer rate, low power and ease to use are the key features that made USB as an industry standard **data** transmission interface. Hot plugging can be achieved automatically in USB interface. Without shutting down the system, USB can connect the computer with electronic devices. A RS232 dependent system can be easily portable to USB interface by using embedded RS232 to USB converter. To bridge the difference in **data** rates among the 2 interfaces first-in first-out (FIFO) logic is used. The study of USB protocol with an FPGA development board is important. The USB standard interface broadly has 2 units, Parallel interface engine (PIE) and USB transceiver macro cell interface (UTMI). PIE is accountable for packet extraction or construction and also responsible for the communication with the peripherals. UTMI is connected to USB cables and are used for transmission of serial **data** and for synchronization of time frames. The serial interface engine (SIE) has two sub-blocks, Endpoint Logic sub-block and SIE control sub-block. The endpoint logic block has, FIFO, FIFO logic and endpoint number recognition. The SIE block has sequencing logic for USB packets and transactions managing, logic of address recognition and USB product identification logic (PID). SIE blocks lies in between the processing unit of computer and UTMI. It receives the **data** from the computer processor and transmits to the UTMI. The UTMI unit does clock synchronization, clock recovery, bit stuffing, **data** serialization and deserialization. UTMI uses differential signals to transmit **data** from one USB to other USB compactable device.