通过单片机扩展8255，输出8421编码，控制继电器，实现对电阻输出阻值的可编程控制。系统采用6位LED数码管显示，4x4键盘。可设置多组要输出的阻值，并可以上系统单步或连续输出阻值。主要作为一些需要输入阻值系统校验信号.

-Extended by the microcontroller 8255, output 8421 coding, control relays, to achieve the output resistance of the resistor programmable control. System with 6-digit LED display, 4x4 keyboard. Can be set to output multiple sets of resistance, and the above single-step or continuous system output resistance. Mainly as a resistance system that need to check the input signal.