Kjetil's Information Center: A Blog About My Projects

Commodore 64 RS-232 Interface

By using a TTL-level RS-232 to USB converter, like this one, it was surprisingly easy to connect the Commodore 64 to a Linux box. I read somewhere that an inverter was required on the RxD/TxD signals, but during my testing with this converter, that was not necessary. This means you only need wires, and no additional electronics!

The RS-232 interface is found on the C64's user port, and the wiring is as follows:

C64 Signal:   C64 User Port:   Converter:
Ground        A + N            Gnd
RxD           B + C            TxD
TxD           M                RxD 

The best terminal program for the Commodore 64 is NovaTerm, since it supports VT102/ANSI emulation and such.

Assuming the converter is connected to a Linux box and detected as /dev/ttyUSB0, the connection can be tested like this at 1200 baud, which is the most common:

screen /dev/ttyUSB0 1200

To provide a login prompt at 1200 baud and supporting ANSI escape characters, something like this can be run as root:

agetty -L ttyUSB0 1200 ansi

Here's a "screenshot" of NovaTerm 9.6c connected to a Linux box and running top:

Screenshot of top via NovaTerm.

Topic: Configuration, by Kjetil @ 19/01-2013, Article Link