This paper first begin with the connotation of virtual instrument technology , study and discuss the criterion and the working theory of usb deeply . on the principle of usb1 . 1criterion , using usb interface chip usbn9604 and low consumption mirochip c8051f231 , we designed the available interface of usb bus and its controlling software , turn the communicating function based usb bus between computer and testing device . second based on the developed interface of usb bus , using microchip pic16c62 and a mount of relays , we designed the multiswitching scanner and its controlling software to complete the funtion of accesses swithing in testing system . third calling the api function inside the windows using vb programming language , communicat with the impelling program of selected hid , achieve the function of testing instrument with usb interface , complete the development of upside software faced testing . at last , based on the deep studying of pcb testing method , used the developed multiswithing scanner and software faced testing , combinated with necessary testing instrument , we constructed the pcb testing system and analized the testing result simply 论文首先从虚拟仪器的技术内涵出发，深入研究和讨论了通用串行总线usb规范及工作原理，并依据usb1 . 1规范，采用usb接口芯片usbn9604和低功耗微处理器c8051f231设计开发了通用的usb总线接口及其控制固件，实现了通用计算机与测试设备之间基于usb总线的通信功能；其次，在所开发的usb总线接口的基础上，使用微处理器pic16c62和多路继电器开关，设计开发出实现测试系统中测试通道切换功能的多路通道扫描器及其控制固件；再次，采用vb语言编程，调用windows内部api函数，与选定hid类驱动程序进行通信，实现usb总线接口测试仪器功能，完成面向测试的上层软件开发；最后，在深入研究印刷电路板测试方法的基础上，利用已开发的多路通道扫描器和面向测试软件，结合必要测试仪器组建印刷电路板测试系统，并对测试结果进行了简要的误差分析。
Second based on high performance dsp - tms320c32 , design and realizing the hardware of the system - mainboard of data collecting and processing . it includes 1 ) external memory system 2 ) the interface of accelerators and fog 3 ) dart 4 ) boot loader 5 ) decoding and reset system 6 ) interface of jtag 为了实现系统功能，系统板在硬件上主要具备了以下结构： 1 )外部扩展存储器系统； 2 )陀螺反加速度计接口电路； 3 )通用异步串行口电器( uart ) ； 4 )程序引导装载电路； 5 )译码反复位电路； 6 ) jtag接口。
