C64 RS232 User portAvailable on the Commodore C64/C128. Software emulated. The signals does not have true RS232 levels. It´s TTL level, and RXD/TXD is inverted. It´s just the normal User port, used as a RS232 port.
C64 Serial I/OAvailable on the Commodore C64, C16, C116 and +4 computers
CoCo Serial PrinterAvailable on the Tandy Color Computer, also known as CoCo.