串口通信，用串口实现对继电器的控制，用到JMDM-40DIOMR继电器-Serial port communication, with serial realize the relay control，Use JMDM- 40 diomr relay

read sub-buffers thus in cases where read(2) is being used to drain the channel buffers, special-purpose communication between kernel and user isn t necessary for basic operation. -read sub-buffers thus in cases where read(2) is being used to drai