modbus协议说明，原版资料，最权威。modicon官方资料。(Modbus protocol specification, the original data, the most authoritative. Modbus protocol specification, the original data, the most authoritative)

在官方找到的modbus协议，不过可惜是英文版的，但应该也能理解。(The Modbus agreement found by the authorities is unfortunately English, but it should also be understood.)