Stormbringer (48k): Routine at 63657

63657: If Kempston joystick is not present then revert to previously selected input device

Used by the routine at 63598.

Input
B	Index of currently selected input device
D	Index of previously selected input device

Output
B	Index of currently selected input device if Kempston joystick is present, otherwise index of previously selected input device

63657

IN A,(31)

Load A with current Kempston joystick state

63659

AND 224

If bits 5, 6 and 7 (i.e. unused bits) are reset, indicating presence of Kempston joystick...

63661

RET Z

...then return

63662

LD A,D

Load A with index of previously selected input device...

63663

LD (63653),A

...set as currently selected input device...

63666

LD B,A

...and load into B

63667

RET

Return