说明：  1、通过DLL与PLC通信，基于ppi协议。 2、DLL文件名：S7_200_PPI.dll 3、串口，连接线为西门子PC-PPI电缆或自己焊接 4、S7-200 PLC 默认参数即可 5、默认一次最多读取100个VB字节或50个VW字，通过修改相关参数，可以读取更多 6、为了简化程序，仅提供V区操作，实际应用中足够了 7、操作VW字时，地址应为偶数
(1, by the DLL to communicate with the PLC, based on the ppi agreements. DLL file name: S7_200_PPI.dll 3, serial cable for Siemens PC-PPI cable or welding 4, S7-200 PLC default parameter to 5, the default up to read 100 VB bytes or 50 VW word, by modifying the relevant parameters, you can read more 6 V region of operation, in order to simplify procedures, only in the practical application of sufficient 7 operating VW words, the address should be an even number)