实时时钟 基于单片机89C52 1302 不过 掉电的时候 时间就停止，重新上电后 ，出现的时间为掉电后的时间。-Real-time clock-based microcontroller 89C52 1302, but the power-down when time stops, power on again, time after power-down time.

基于89c52的PWM产生程序，简单易懂-The PWM generator based on 89c52, easy to understand

89C52驱动AD9959的简单程序 已验证可用(The simple program that 89C52 drives AD9959 has been verified to be available)