基于51单片机的spi通信协议，模拟IO口输出-Based on 51 SCM spi communication protocols, analog IO port output

nrf24L01底层驱动,使用单片机IO模拟SPI,简单易行,很容易移植,文件是针对MSP430而写,我也已移植51,STM8等单片机中运行.-nrf24L01 underlying driver, use microcontroller IO simulation SPI, simple, very easy to transplant, the file is written for MSP430, I have also been transplanted 51, STM8 microco