A part answering at one address, with every register reading zero.
The address the part answers to.
How many transfers the part has served.
Puts bytes in the part from a register on. Past the last register they wrap to the first.
What consecutive registers hold, from one register on.
What one register holds now.
A part that is not there, answering from 256 registers.
A write names a register and fills it and the ones after it; a read takes them back from wherever the last write left off. What a driver writes stays written, so a program reads a part's configuration back once the driver is done with it.