Changes
ld bc,&f792 ;; PPI port A input
out (c),c
ld bc,&f649 ;; select keyboard row 9 (joystick 0)
out (c),c
update_loop:
ld bc,&f649 ;; select keyboard row 9 (joystick 0) out (c),c
ld b,&f4
in a,(c)
ld bc,&f640 ;; deselect keyboard row 9 (by selecting keyboard row 0)
out (c),c
jp update_loop
