实现程控电压电流源的程序.在功能方面，要求通过单片机按键选择输出信号类型及要求的输出量，并在显示器件上指示信号类型及设定数值-Voltage controlled current source to achieve the process. In the function, called for the adoption of single-chip button and select the output signal of the type of output required and th