var master = ModbusSerialMaster.CreateRtu(port);
master.Transport.ReadTimeout = 2000;
//其中transport还有重试次数和重试间隔时间，默认是3和250
//master.Transport.Retries + "  " + master.Transport.WaitToRetryMilliseconds;

步骤三：设置协议参数，开始读写

 byte slaveID = 3;
ushort address = 1;
bool[] coils = new bool[8];
coils = master.ReadCoils(slaveID, address, 1);

以上面方式读线圈，超时就会抛出异常。

可选步骤四：以async await方式读写

比如点击按钮之后，调用AcquireStatus 方法

        private async void AcquireStatus(ModbusSerialMaster master)
            byte slaveID = 3;
            ushort address = 1;
            bool[] coils=null;
            master.Transport.ReadTimeout = 2000;
            try {coils=await master.ReadCoilsAsync(slaveID, address, 1); }
            catch (Exception ex)
                MessageBox.Show("your value " + "无返回值");
            if (coils != null)
                this.checkBox1.Checked = coils[0];
                MessageBox.Show("your value " + coils[0]);