The asynchronous sampling of EAST power supply data acquisition system could be caused by the data acquisition cards working ontheir own clock. The unified external clock signal canbe used to make the sampling synchronous. Meanwhile the signal should be controlled and configured via Ethernet. Through the research found that circuit based on AVR microcontroller and ENC28J60 Ethernet chip can meet the requirement. The scheme includes the components selection and circuit design of power supply and network jack, ENC28J60 driver writing, the program design ofexternal clock signal outputting and the waveform shaping. According to the test, every DAQ card of EAST power supply data acquisition system can work on unified clock signal which controlled by upper-computer via Ethernet with this method.%EAST电源数据采集系统的多道信号之间存在采集不同步的问题。这是由于每个采集单元的采集卡在各自的时钟下工作造成的。使用统一的外部源可以同步采集卡的时钟以达到同步采集的目的，同时外部时钟系统需要能被控制网通过以太网控制和配置。基于ATmega16单片机和ENC28J60以太网芯片的电路可以实现以太网控制的外部时钟系统。此方案包含系统的电源电路的选型与设计、网络接口的选型与电路设计、ENC28J60驱动程序的编写、时钟信号输出程序的设计与时钟信号的调理。最终通过实验调试采集到的波形，表明此方案可以通过以太网更改配置并输出不同频率的时钟信号，达到了预期的设计目标，为EAST电源数据采集系统提供统一的外部时钟。
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