Re: Sinclair Spectrum considerations
As far as I know both Sinclair and Kempston interfaces expected joysticks with the same Atari-compatible wiring to be plugged into their 9-way 'D' connectors. The difference was in the interface hardware and therefore the software method used to read them.
The original 'official' Sinclair twin joystick interface was part of the 'Interface 2' which also included a cartridge slot. The interface hardware made movements and button presses on the joysticks look like key presses on the numeric buttons 1-5 and 6-0 on the keyboard, as mentioned earlier.
The Kempston interface - for one joystick only - translated the joystick / button states into a single byte value which could be read in with an IN (31) ? instruction.
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