Hard to find any supporters of i2c these days. To be 100% compatible, sda and scl must be bi-directional. Complicates bus buffers; also complicates a bit-bang

Hard to find any supporters of i2c these days. To be 100% compatible, sda and scl must be bi-directional. Complicates bus buffers; also complicates a bit-banging implementation. In the olden days, this was fairly easy by having an input on each pin, with the pull-down transistor per pin as shown in the article. The main drag about SPI is this Phase and Polarity. Being opinionated (!) I wish the SPI were were all CPHA=0 and CPOL=0 (bits clock in on the positive-going edge).