采用IO口模拟I2C总线时序的方式，将数字信号送到芯片内部，通过芯片内部的DA转换功能，根据参考电压，输出一个电压值。然后将DA转换的结果经过闭环连接到AD的输入管脚，经过I2C的读操作，可以读出AD转换的值。-Use IO I I2C bus timing simulation of the way, the digital signal sent to the chip, through the DA conversion chip, according to the reference voltage, outputs a voltage. The result of DA conversion and then loop through the input pin to connect to AD through I2C read operation, you can read the value of AD conversion.