Design of USB virtual oscilloscope
The entire system adopts a hardware structure based on cache, local bus, high-speed DSP, etc. It contains a complete data acquisition and processing system, but it also has the characteristics of a test instrument, which is mainly reflected in analog amplification, gain control and a series of high-speed control circuits; the local bus is the core of the data acquisition system and constitutes the system Each module is connected to the local bus; the cache is divided into two channels, which are respectively responsible for the upstream and downstream communications between the communication interface and the DSP. The communication interface of the data acquisition system can be implemented using various methods, such as the IO port of the PC computer, memory window mapping, DMA, etc. In this article, USB interface transmission technology is used to achieve the purpose of meeting higher communication rates.
When the prescribed trigger conditions are met, the high-speed control circuit in the data acquisition system starts the AD converter. The converted data is in the DSP. The DSP calculates the results required by the PC computer based on the algorithm preset by the PC computer and stores them in the cache. , and notify the PC computer to retrieve the data. After the PC computer retrieves the data, it restarts data collection and waits for the trigger condition to be met again.
The communication protocol between the data acquisition system and the PC computer is a passive protocol. In the hardware module of the virtual instrument system, the function completed by the pc computer is to provide a human-machine graphical interface and control data acquisition work. Various processing algorithms are run in the dsp. When the pc computer initializes the acquisition card, in addition to completing the necessary register assignments, Also load the running program for dsp.
USB Technology of USB Virtual Oscilloscope
The USB technology is proposed based on the use of universal connection technology to achieve simple and fast connection of peripherals, so as to facilitate users, reduce costs, and expand the range of peripherals connected to PCs. It makes the function expansion of PCs very simple and can maximize the Reduce the user's demand for computer technology and make all peripherals so-called "fool" devices. USB specifications can provide different options for different performance-price ratio requirements to meet different systems and components and corresponding different functions. The main advantages are as follows:
(1) Ease of use for end users;
(2) Wide applicability;
(3) Synchronous transmission bandwidth;
(4) Flexibility.
USB technology is open, a non-profit specification, and has received extensive industrial support. It has been widely used in digital images, telephone speech synthesis, interactive multimedia, consumer electronics and other fields.
System structure of USB virtual oscilloscope
The structure of a complete virtual instrument system is generally divided into four layers:
1. Test management users use applications developed by virtual instrument manufacturers to form their own set of test instruments. This is one of the advantages of virtual instruments. It allows users to easily build their own test instruments according to their own needs and style.
2. The application (program) development layer consists of software development tools provided by manufacturers, such as NI (NATIONALINSTRUMENTS)'s LabVIEW software and LabWindows/CVI software. Users can use this type of software for in-depth development to expand the original functions of the instrument.
3． The instrument driver layer is developed by the manufacturer and has different driver interfaces for different types of instruments. In order to provide users with convenient and easy-to-use instrument drivers, 35 of the world's largest instrument companies, including Tektronix, Hewlett-Packard and National Instruments, established the VXIplug&play system alliance and launched the VISA (Virtu-al Instrument Software Architecture) standard.
4． The I/O bus driver layer is developed by manufacturers to connect different types of actual instruments through the same standard bus to form a complete test system, such as the widely used VXI (Open Measurement System) bus system.
