说明：  Modbus 主站串口通信程序，主要可以实现与Modbus 从站设备的连接，本程序主要用于与ABB变频器的连接，可以控制电机的起停与控制。
(Modbus master serial communication procedures, can be achieved mainly with Modbus slave devices connected, this program is mainly used for connecting ABB drives can be controlled with the start-stop control of the motor.)