频率计的程序：包含外部中断设置，中断服务程序，定时程序，定时服务程序 以及数据处理，显示，包括 三位十进制数转化为四位BCD码。-Frequency Counter program: Includes external interrupt settings, the interrupt service routine, regular program, regular service program　and data processing, display, including three of four decimal numbers into BCD code.