非常详细的modbus规范介绍，有串口的也有基于tcp的。。。。一书在手，modebus不用愁。。。。MODBUS标准分为三部分。第一部分（“Modbus协议规范”）描述了MODBUS事物处理。第二部分（“MODBUS报文传输在TCP/IP上的实现指南”）提供了一个有助于开发者实现TCP/IP上的MODBUS应用层的参考信息。第三部分（“MODBUS报文传输在串行链路上的实现指南”）提供了一个有助于开发者实现串行链路上的MODBUS应用层的参考信息。-very detailed Modbus standard, a serial port is based on the tcp. . . . A book in hand, do not have to worry about modebus. . . . MODBUS divided into three parts. The first part ( "Modbus protocol specification") describes the MODBUS handle things. The second part ( "MODBUS Packet Transmission in TCP/IP Implementation Guide"), provides a help developers to implement TCP/IP on the application layer MODBUS reference information. The third part ( "MODBUS Packet Transmission in the serial link achieve Guide"), provides a help developers achieve serial MODBUS link on the application layer of reference information.