利用51系列单片机设计一个24小时制电子时钟，电子时钟的时、分、秒数值分别通过P0、P1、P2端口输出（以压缩BCD码的形式）。P3.0为低电平时开始计时，为高电平时停止计时-Use of 51 series microcontroller design a 24 hour system electronic clock, electronic clock, points, second respectively through numerical P0, P1, P2 port output (in compression BCD code form). P3.0 for low electric usually at the beginning of time, for high electric usually stop the clock