Kempston Joystick Interface

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Until the release of the +2 and +3, the Kempston joystick interface and its compatibles were the most common Joystick interfaces available to Speccy owners.

The original version also worked with the ZX-81, but joystick support in ZX81 games was much less common.

The interface uses standard Atari-style joysticks.

Port $1f

Bits are active high so 00=nothing pressed.

Bit Mask Usage
0 00000001 Right
1 00000010 Left
2 00000100 Down
3 00001000 Up
4 00010000 Fire!
5 00100000 Very occasionally a second fire button on some clones, but usually 0
6 01000000 Always 0
7 10000000 Always 0