M103 -- O2 sensor and X11 pin 3 relationship

[sixto]

What's the relationship between the O2 sensor reading and the reading at pin 3 of the X11 diagnostic port?

I've seen the O2 sensor reading oscillate in a range between 0-1V as it should and read that the voltage at pin 3 should be somewhere between 6.8-7.2V. What happens in between?

Thanks,
Sixto
91 300SE
87 300SDL