用MSP430 launch pad制作一个简易的方波信号发生器，要求：

使用MSP430的Timer_A产生方波信号，方波信号频率范围：1KHz~10KHz

方波信号的频率由外部电压控制，电压范围为0-2V，输入电压和输出频率呈线性关系；

外部电压信号由MSP430的片内A/D采集；

外部输入电压由电位器产生；

输出信号的频率误差<10Hz；

系统上电以后默认输出方波信号1kHz。

增加按键控制功能，当S2（P1.3)按下时，通过改变外部输入电压可控制方波信号频率，当S2（P1.3）松开后，外部输入信号对方波信号输出频率无影响。-The pad produced a simple square wave signal generator, the MSP430 launch requirements: MSP430 Timer_A produce a square wave signal, a square wave signal frequency range: 1KHz ~ 10KHz　the frequency of square wave signal is controlled by an external voltage, the voltage range of 0- 2V input voltage and output frequency is a linear relationship　external voltage signal from the MSP430 on-chip A/D acquisition　external input voltage generated by the potentiometer　default output square wave signal in the output signal of the frequency error < 10Hz　system power after 1kHz. Increase the key control function of S2 (P1.3) is pressed, by changing the external input voltage square wave signal frequency can be controlled, no effect of S2 (P1.3) release, the square wave signal output frequency of the external input signal.