AT89S51为控制MCU；采集按键信息进行不同的功能输出：
　　　　　　标准输出1K正弦波、1K方波、1K三角波、1K锯齿波；
　　　　　　在其基础上进行正弦波、方波、三角波、锯齿波频率可调；
　　　　　　信号频率控制值原理：由于DAC数据转换的时间是有芯片本身的特性所决定的故方案设计里通过控制转换频率
　　　　　　和转换的点数来达到对信号频率的控制(AT89S51 controls MCU, and key information is collected for different function output.
Standard output 1K sine wave, 1K square wave, 1K triangle wave and 1K sawtooth wave.
The frequency of sine wave, Fang Bo, triangle wave and sawtooth wave can be adjusted based on it.
The principle of signal frequency control value: because the time of DAC data transformation is determined by the characteristics of the chip itself, the conversion frequency is controlled in the design.
And convert the number of points to achieve the control of signal frequency.)