[julie_m]

It's very possible there may have been an address clash between the AMX mouse and the 128K Spectrum hardware extensions. Even if so, you could always build your mouse interface to sit on different addresses and patch the software to suit. I used to be able to look at a column of hex numbers and see the instructions in my mind's eye, back in the days .....

For extra hacker cred points, use a PIC microcontroller to talk to a modern PS/2 or USB mouse (a USB mouse may be able to speak PS/2 if it decides it is not plugged into a proper USB port, even if no adaptor was supplied with it; they probably all use the same ICs internally) and output the same XA, XB, YA and YB signals as an original AMX mouse!