USB Virtual Oscilloscope Design
Based on the computer technology of modern instrumentation has also developed rapidly, the virtual instrument came into being, in the precision, stability and other aspects of the requirements of high occasions, the virtual instrument will gradually replace the traditional instruments. USB virtual oscilloscope using USB interface technology, the computer's powerful computing and processing capabilities and general hardware instrument signal acquisition, control capabilities combined together, so as to achieve the general oscilloscope can not be realised! The whole system adopts high-speed cache and local interface.
The whole system adopts the hardware structure which is mainly based on high-speed cache, local bus and high-speed dsp. It contains a complete data acquisition, processing system, but it also has the characteristics of the test instrument, which is mainly manifested in the analogue amplification, gain control and a series of high-speed control circuits; local bus is the core of the data acquisition system, composed of the system of various modules are hooked up to the local bus; high-speed cache is divided into two, respectively, is responsible for the communication interface and the dsp between the uplink and downlink communication. The communication interface of the data acquisition system can be achieved using various methods, such as pc computer io port, memory window mapping, dma, etc.. In this paper, usb interface transmission technique is used to achieve the purpose of meeting higher communication rate.
When the specified trigger conditions are met, the high-speed control circuit in the data acquisition system starts the work of ad converter, the transformed data is in the dsp, the dsp calculates the results needed by the pc computer according to the algorithm pre-set by the pc computer, stores them in the cache, and notifies the pc computer to take the data, and the pc computer takes out the data and then restarts the data acquisition and waits for the trigger conditions to be again Satisfaction.
The communication protocol between data acquisition system and pc computer is passive protocol. In the hardware module of the virtual instrument system, the pc computer completes the function of providing man-machine graphical interface and controlling the data acquisition work, various processing algorithms run in the dsp, the pc computer initialises the acquisition card in addition to completing the necessary register assignments, but also for the dsp to load the runtime program.
