Microcomputer Virtual Signal Generator Based On USB Communication Technology

The virtual instrument combining computer resources with the measure function of instrument hardware is a great development in the progress of instrument, which fully makes use of the hardware and software resources of computer and stands for the new times of instrument development. The interface of USB has much superiority, such as real plug and play, flexibility, a max transmitting velocity of 480 Mb/s, low cost, high reliability, and saving system resources and is regarded as a sharable interface. Thus the USB interface is used to generate two-way phase adjustive signal generator in this paper.The developing methods and realizing process of the signal generator are studied from hardware and software aspects in detail. In the hardware aspect, USB2.0 interface circuit, FIFO interface mode between USB chip and CPLD, interface circuit of CPLD and memory, and D/A circuits are all discussed. After designing the firmware, this paper significantly analyzes the realization of the system driver program and the mainframe application program. In the firmware part, software structure and the interrupt system of USB chip are introduced. Based on the discussing of the WDM structure, driver program part gives the flow chart and the design method of the key functions. The application program includes the mainframe interface design, application program and driver program interface design. Experiment results show that, the signal generator based on USB interface designed in this paper is low-cost, flexible, convenient and practical.