Commodore 64

Content coming soon...

• https://www.commodore.ca/manuals/funet/cbm/schematics/computers/c64/manual-html/Page_14.html
• https://www.hvsc.c64.org/
• https://www.c64-wiki.com/wiki/CIA
• https://www.c64-wiki.com/wiki/User_Port
• https://www.freepascal.org/~daniel/c64pla/

For now, see Commodore 64 on Wikipedia.

The picture on Wikipedia is immaculate and cannot be improved upon.