From SpecNext official Wiki
|Short desc.||Sets and reads the I2C SDA line|
|Bit Mask||%0001 0001 0011 1011 ??|
When write, it sets the SDA line, D0 --> SDA When read, it reads the SDA line, SDA --> D0
Note that I2C uses open collector outputs, the idle, released state is '1'. So if you want to read the line, you have to set it to '1' first.