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 w

CRC校验码，用于modbus，可以保证传输数据不出错(CRC check code, used in modbus, can guarantee the transmission of data without error)