设计一个由单片机控制的信号发生器。运用单片机系统控制产生多种波形，这些波形包括方波、三角波、锯齿波、正弦波等。信号发生器所产生的波形的频率、幅度均可调节。并可通过软件任意改变信号的波形。

基本要求：

1.　　产生三种以上波形。如正弦波、三角波、矩形波等。

2.最大频率不低于 500Hz。并且频率可按一定规律调节，如周期按1T,2T,3T,4T或1T，2T，4T，8T变化。

3.幅度可调，峰峰值在0——5V之间变化。

扩展要求：产生更多的频率和波形。

-To design a microprocessor controlled signal generator. Control the use of SCM systems produce a variety of waveforms, these waveforms include square, triangle wave, sawtooth, sine wave and so on. Waveform generated by signal generator frequency and amplitude can be adjusted. Can be arbitrarily changed by software, the signal waveform. Basic requirements: 1. Have three or more waveforms. Such as sine, triangle, rectangle wave. (2) maximum frequency of not less than 500Hz. And adjust the frequency according to certain rules, such as the cycle by 1T, 2T, 3T, 4T or 1T, 2T, 4T, 8T change. 3 adjustable amplitude, peak to peak in the 0- 5V between changes. Extended requirement: to produce more frequency and waveform.