I'm referring to line codes like bipolar, machester, miller etc... https://en.m.wikipedia.org/wiki/Line_code
How do these line codes relate to bus protocols?
Is it another level down? Is it hardwired into the metal like with Ethernet? Are they used for completely different purposes like how we have CDMA for phonecalls but ADSL for Internet?
Or could we customize a SPI interface to generate any number of line codes based on combinations of polarity and alpha (i.e. high/low on rising/falling edge)