//写的时候，是低电平改变数据，上升沿送入数据

//读的时候，是低电平读入数据，下降沿使得从设备把数据放到总线上

//读的时候，是低电平读，但没有读出，提供下降沿使得从设备把数据放到总线上-//Write time, change the data is low, rising edge into the data// time when data is read into the low-level, falling edge enables data from the device on the bus// time when is a low-level reading, but did not read out, making the provision of falling on the data from the device bus