After 1985 became the IEEE802.3 standard, in the process of increasing the data transmission speed from 100Mb/s to 100 MB/s, computers and network industries are also trying to solve the problem of insufficient timing synchronization ability of Ethernet, and have developed a software-based network time protocol (NTP) to improve the data transmission speed. The synchronization accuracy of NTP version 1992 can reach 200μs, but it still cannot meet the accuracy required by measuring instruments and industrial control. In order to meet the needs of distributed network time synchronization in measurement and control applications, the establishment of network precision clock synchronization committee was proposed at the end of 2000, and in 20001year, IEEE Instrument and Measurement Committee and American Institute of Standards and Technology (NIST) proposed the establishment of network precision clock synchronization committee, which was supported by engineers and technicians with the same interests in information technology, automatic control, artificial intelligence, testing and measurement. The specification drafted by this committee was adopted by IEEE Standards Committee as IEEE 65438+ at the end of 2002. The full name of IEEE 1588 is the protocol standard of precise clock synchronization for network measurement and control system. The draft IEEE 1588 standard is based on the related achievements of Hewlett-Packard Company from 1990 to 1998. In other words, Agilent Technology has made an important contribution to the IEEE 1588 standard. John Eidson, a senior researcher at Agilent Labs, is regarded as an expert by the network industry. His two papers, The Application of IEEE 1588 in Test and Measurement System and The Application of IEEE 1588 in Measurement and Control and Communication, gave an incisive and comprehensive introduction to the IEEE 1588 protocol. IEEE 1588 protocol is a general specification to improve the time synchronization ability of network systems. In the process of drafting, Ethernet is mainly used as reference, so that the distributed communication network can have strict time synchronization and be applied to industrial automation systems. The basic idea is to synchronize the internal clock of the network equipment (client) with the main clock of the main controller through hardware and software, thus providing the use of synchronization setup time less than100μ ss. Compared with Ethernet delay time 1588, the timing synchronization index of the whole network has been significantly improved. Here is a brief description of the characteristics of IEEE 1588: the early network time protocol (NTP) only had software, while IEEE 1588 used both software and hardware to achieve more accurate time synchronization; GPIB bus has no synchronous clock transmission, so it relies on parallel cables and limits the cable length (the distance of each device) not to exceed 5m to ensure that the delay is less than 30μ s; The data line and control line of GPIB are separated, and VXI and PXI buses extend on VME and PCI computer buses respectively, and clock lines should be added. IEEE 1588 still uses the original Ethernet data line to transmit the clock signal, and no additional clock line is needed, which simplifies the networking connection and reduces the cost. The clock oscillator drifts with time, which requires the calibration of standard timing system, and the calibration process should be shortened, safe and reliable. At present, GPS (Global Positioning System) and IRIG are commonly used. B (international universal time format code), IRIG? B sends a frame pulse and a 10MHz reference clock every second to realize clock synchronization between host and client. IEEE 1588 adopts the concepts of time allocation mechanism and time scheduling. The client can use an ordinary oscillator to keep synchronization with the host's master clock through software scheduling. The process is simple and reliable, and a large number of clock cables are saved. The introduction of IEEE 1588 is still short, which needs to be improved and revised. For example, a transparent network with hubs and switches can provide good timing synchronization, but it does not overcome the uncertain network timing with routers. At present, a network switching chip which can measure the incoming delay and automatically compensate the delay is being designed and trial-produced. In addition, the complete chip of IEEE 1588 has not been released, and only the replacement chip based on FPGA is available. Intel has announced that it will produce a complete IEEE 1588 chip supporting Pentium processors as soon as possible. In industrial automation, IEEE 1588 was adopted earlier, and many articles were published, especially in automatic control and data acquisition. Symmetricom Company, which specializes in providing network time servers, has introduced a turbine control system. Various sensors in the front end are connected to the data acquisition board, and the precise clock installed on the board is synchronized with the master clock of the system through the Ethernet of IEEE 1588 protocol, so that the synchronization time of the sensors occurs within 1 μ s, and 200 measurements are taken every second, with the measurement interval of 5ms, and the rotation time of the sensors is1μ s. After time alignment, various measurements in the system are controlled. This Ethernet data acquisition system based on IEEE 1588 protocol saves a large number of cables connecting each sensor, realizes accurate timing synchronization, facilitates remote control and measurement, and reduces the cost, which has attracted the attention of the industry. Does the current industrial automation use IRIG? B format time code, the daily accuracy is less than 1 μ s, it should be noted that IEEE 1588 has the potential to further improve the daily accuracy of the control system to 100ns. The reason is IRIG? B time code should send 1 clock pulses per second to each measuring device, and use pulses to send daily time stamps, while IEEE 1588 protocol can directly send daily time information from the master clock to the client clock, which is more advantageous. According to the development trend, Ethernet with IEEE 1588 protocol will occupy the market in industrial automation system. Similarly, the Ethernet of IEEE 1588 protocol solves the bottleneck of long delay time and poor synchronization ability of general Ethernet, and will obviously play a greater role in the application of measuring instrument system. The instrument extension interface LXI of Ethernet is actually a new generation of measuring instrument interface. It is an Ethernet based on IEEE 1588 protocol, equipped with other conditions required by the measuring instrument system, and absorbs the characteristics of VXI and PXI GPIB.