The Nimbus PC-186 used a non standard keyboard protocol.
It used the XT scancode
The keyboard also doesn't produce its own clock signal like a normal XT but instead works on 9600 baud.
It used inverted TTL protocol (essentially rs232 but at lower voltages)

The example above is a typical version, produced by Alphameric (Woking, UK)
It used foam and foil switches.

After 30 years of use, the ones here in the museum needed a clean!