Port decoding to be confirmed.
FBEE is xxxx x0x1 xxx0 xxx0
FBEF is xxxx x0x1 xxx0 xxx1
FAEF is xxxx x0x0 xxx0 xxxx
In Spectrum interface A10 chooses X,Y. On CPC interface A0 chooses X,Y.
In Spectrum interface A8 chooses buttons or directions. On CPC interface A8 also
chooses this.
Number of mouse buttons supported to be confirmed.