说明：  串口操作继电器，在做下位机通信时往往会用到串口，包括下位机将数据传输给上位机，或者是下位机与下位机之间进行数据传输，这时候就会遇到发送数据的问题，单片机通过串口发送数据时往往是一次一个字节（8位）
(Serial operation relay The serial port is often used in the communication of the lower computer, including the transmission of data to the upper computer by the lower computer or the data transmission between the lower computer and the lower machine. At this time, the problem of sending data will be encountered. When the MCU sends the data through the serial port, it is often a single word node (8 bits).)