Int 15 Fn 84  - BIOS - Joystick Support (xt After 11/8/82,at,xt286,ps)     [B]

   AH = 84h
   DX = subfunction
       0000h read joystick switches

       Return: AL bits 7-4 = switch settings
       0001h read positions of joysticks

       Return: AX = X position of joystick A
           BX = Y position of joystick A
           CX = X position of joystick B
           DX = Y position of joystick B

Return: CF set on error
       AH = status
       80h invalid command (PC,PCjr)
       86h function not supported (other)
   CF clear if successful

Notes: if no game port is installed, subfunction 0000h returns AL=00h (all
     switches open) and subfunction 0001h returns AX=BX=CX=DX=0000h
   a 250kOhm joystick typically returns 0000h-01A0h