A Study Of Unilateral Data Transferring System Based On USB Bus

USB bus is a kind of general serial bus. It has been widely used in various kinds of data transferring equipment because it is convenient, easy to handle, quick and cheap. Nowadays most of the host computers are equipped with USB interfaces. It is said that USB technology will be applied in all bus interfaces in the future. USB interface technology provides a wonderful solution for the data transmission between PCs.On some special occasions, for instance, when transferring files between an internal network with high security requirement and a public internet network, files and data are required to be only transferred from a PC linked with the public internet network to a PC linked with the internal network, namely, unilateral data and files transmission with high security and at high speed. Even though the PC linked with the internal network was illegally controlled, those data and files can not be transferred reversely. By making use of USB bus files and data can be transferred quickly; by making use of the controlling feature of SCM they can be safely transferred unilaterally.This thesis provides a scheme for transferring data and files between two PCs by making use of USB bus technology. We designed a USB facility. It has two USB bus interfaces. One is the master computer port; the other is the slave computer port,whichcan be linked with two PCs respectively. Files and data can only be transferred from the master computer port to the slave computer port, but can not be transferred reversely. We use P89V51RD2 SCM as major controlling MCU, PDIUSBD12 as bus controller. Through MCU's initialization of the parts of the PDIUSBD12 and responding to the USB bus events, data and files transferring can be realized.We guarantee the unilateralism of data transmission at the level of both hard ware and software. At the level of hardware, P89V51RD2 has a SPI bus interface, which can be set as master computer and slave computer. According to the interfacing character of SPI bus, its MOSI can be designed as master computer output/slave computer input data bus; MISO as master computer input/slave computer output data bus. When SPI bus is at work, the data on the two buses are transferred reversely and bilaterally. When designing the hardware, we only linked the MOSIs between the master computer and the slave one, but not MISOs. In this way, data can only be transferred unilaterally from the master computer to the slave one, and there is no way to realize reverse transmission. Besides, we can make use of photovoltaic coupling chip.by making use of photovoltaic coupling chip.signals can also be transferred unilaterally.At the level of software, the master computer port receives data from the USB ISR of the PC, and during the ISR transfers them to the MCU of the slave computer through SPI bus. The master computer has no service routine for reading the data from the SPI bus, and no service routine for MCU to transfer data through USB bus. The MCU of the slave computer read the data from the interruption of the SPI bus, and transfers them to the master computer in the USB ISR. The slave computer doesn't transfer data from the service routine of the SPI bus, nor receives data from the service routine of the master computer. As a result, the unilateralism of the data transferring from the master computer to the slave computer is guaranteed.