Early PC Keyboard Protocols

Due to patents held on the keyboard interface of the IBM PC, 'clone' manufacturers developed their own keyboard interfaces in the 1980s. Later designs almost exclusively switched to the IBM PS/2 'industry standard' interface.

The electrical protocols used in these various designs differed, meaning that only the particular brand of keyboard could be used with the particular machine. Some brands, such as Tandy, had a reputation for exploiting this fact with their spares pricing.

Protocols

Some direct comparisons of the signalling used in the different designs:

See Also

• Keyboard Signalling Diagrams
• Amstrad Keyboard Interface