| The essay aims at designing the long-distance data-acquisition-system of USB interface. Adopting USB-RS485 interface could make up the disadvantage of data-acquisition-systems which adopt single USB bus or the RS485 bus or RS232 bus. In this way, the following will be achieved in data transfer: high speed, low cost, long distanceand toilless expandability.The system mainly contains two basic segments: RS485-USB interface and data-acquisition unit. And all versions of protocol and construct systems of RS485-USB, growing quickly, are researched deeply in this essay. A Ver2.0 USB control chip(ISP1581) from PHLIPS with high performance-price ratio is selected to design hardware and software and debug. Using MCU+USB scheme we can fulfill the hareware circuit design and firmware programming. By adopting HID driver, we could finish the programming and debugging of the internet applications of host pc so all hardware and software will meet the requirements of USB transmit standard. The essay analyzes and expatiates the scheme of long-distance data-acquisition units which uses the high-speedA/D conversion to transmit simulator into numeric quantum(数字 量) then delivers it to FIFO data buffer. At the same time, using timer 8254, it can provide synchronous trigger pulse. On the one hand, it is used to be the trigger sigal of A/D. On the other hand, it delivers the counter CD4040 in order to provide the right address for FIFO to synchronize theA/D conversion and data's read-in. Based on the scheme the essay explains the hardware design and software program.Through the experiments on the host pc and MCU data transfer, the transmission rate and validity are verified. As the development of USB technology, we will deal with the following three aspects:firmware, mainframe and USB protocol to increase data transmission rate. Also USB complementary protocol and OTG protocol both sustain point-to-point transmission which causes the wider future of the computer system. |
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