$DD00/56576/CIA2+0: Data Port A (Serial Bus, RS-232, VIC Memory Control) +----------+---------------------------------------------------+ | Bit 7 | Serial Bus Data Input | | Bit 6 | Serial Bus Clock Pulse Input | | Bit 5 | Serial Bus Data Output | | Bit 4 | Serial Bus Clock Pulse Output | | Bit 3 | Serial Bus ATN Signal Output | | Bit 2 | RS-232 Data Output (User Port) | | Bit 1-0 | VIC Chip System Memory Bank Select (Default = 11)| +----------+---------------------------------------------------+