ADS7871驱动：使用SPI通讯，实现了ADS7871D的配置，转换，读写

ADS7871为AD转换器，内置可编程的放大器。-ADS7871 for the AD converter, built-in programmable amplifier.

实现模数的精密放大与采样。采用SPI通信，实现差分或单端采样。(Achieving precise amplification and sampling of modulus. SPI communication is used to realize differential or single terminal sampling.)