测试西门子S7-200系列PLC自由口用的例程，时常简洁。正常通信情况下，串口调试助手会不断返回16进制的25 26 27 28 29这几个数据。-Test Siemens S7-200 series PLC free port with routines, often simple. Under normal traffic conditions, serial debugging assistant will continue to return 16 of the 229 25262728