说明：  C51很好的IO模拟串口程序，也称软件UART。只需用一个定时器，实现中断接收。程序编写得很规范，有很多个晶振频率和串口频率可选。是一个比较好的软件串口程序。
(C51 a good simulation of serial IO program, also known as the software UART. Just use a timer to achieve interrupt reception. Programming very standardized, there are many a crystal oscillator frequency and the frequency of an optional serial port. Is a relatively good software serial programs.)