Research And Implementation Of Programming Control Technology For Digital Multimeter Based On USBTMC Protocol

Further expanding the application of USB interface in instrument field,the USB Alliance has introduced the USBTMC protocol,which makes the testing instrument of USB interface get more support from the testing instrument software manufacture.In this paper,the implementation of USBTMC protocol in digital multimeter is the research topic,focusing on USBTMC protocol,SCPI command parsing and the communication mechanism between USB and EEPROM.The main contents have been completed of this research are as following several aspects:1.USBTMC communication function and its realization.According to the USBTMC protocol,the device descriptor in firmware program is changed so that the computer can recognize the digital multimeter as a USBTMC device.Then the data is encapsulated in the firmware and the host computer to conform to the format of the USBTMC protocol2.Construction of SCPI command and design of its parser.According to SCPI Standard Specification and instrument requirement,SCPI command is stored and parsed by HASH table,and the time complexity of SCPI command parsing is optimized from the traditional O(N)level to O(1).3.Software design of PC.The host computer platform developed by CVI can effectively control the digital multimeter through the visa library provided by NI.By separating the configuration phase and the parsing phase into two modules,the coupling of the program is reduced.4.Processing of variable length strings.By introducing MPQ algorithm,variable length strings such as SCPI command strings are transformed into three fixed length HASH values which are stored in EEPROM,thus greatly saving memory space.The parameter strings of SCPI commands are stored by array index,and the string comparison is transformed into numerical comparison,which greatly improves the parsing speed of parameters.