TYPE ModbusCmd :
(
    MODBUS_READ_COILS                := 16#01,    (* 读线圈 *)
    MODBUS_READ_DISCRETE_INPUTS      := 16#02,    (* 读输入线圈 *)
    MODBUS_READ_HOLDING_REGISTERS    := 16#03,    (* 读保持寄存器 *)
    MODBUS_READ_INPUT_REGISTERS      := 16#04,    (* 读输入寄存器 *)
    MODBUS_WRITE_SINGLE_COIL         := 16#05,    (* 写单个线圈 *)
    MODBUS_WRITE_SINGLE_REGISTER     := 16#06,    (* 写单个寄存器 *)
    MODBUS_READ_EXCEPTION_STATUS     := 16#07,    (* 读异常状态 *)
    MODBUS_WRITE_MULTIPLE_COILS      := 16#0F,    (* 写多个线圈 *)
    MODBUS_WRITE_MULTIPLE_REGISTERS  := 16#10,    (* 写多个寄存器 *)
    MODBUS_REPORT_SLAVE_ID           := 16#11,    (* 读从设备ID号 *)
    MODBUS_MASK_WRITE_REGISTER       := 16#16,    (* 写屏蔽寄存器 *)
    MODBUS_WRITE_AND_READ_REGISTERS  := 16#17    (* 读/写多个寄存器 *)
);
END_TYPE