The GamePort of the IBM PC
                       ==========================


First, the pinout:

  1  XY1 (+5v)
  2  Switch 1
  3  X1
  4  Switch 1 (GND)
  5  Switch 2 (GND)
  6  Y1
  7  Switch 2
  8  N.C.
  9  XY2 (+5v)
 10  Switch 4
 11  X2
 12  Switch 3&4 (GND)
 13  Y2
 14  Switch 3
 15  N.C.

You can call BIOS interrupt 15h, subfunction 84h to obtain the button
setting and the joystick position.

I've cut these lines from Ralf Brown's interrupt list release 31.

--------8<--------8<--------8<--------8<--------8<--------8<--------8<--------

INT 15 - BIOS - JOYSTICK SUPPORT (XT after 11/8/82,AT,XT286,PS)
	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

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By the way: it's a good idea to download the newest release of this list...
best source of information anywhere! Here's an archie report...

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Host m.ehd.hwc.ca   (142.4.8.13)
Last updated 18:58 26 Dec 1992

    Location: /pub/msdos/system
      FILE      rw-r--r--    331544  Sep 13 17:48   inter32a.zip
      FILE      rw-r--r--    307988  Sep 13 17:50   inter32b.zip
      FILE      rw-r--r--    165049  Sep 13 17:37   inter32c.zip


Host nic.funet.fi   (128.214.6.100)
Last updated 08:24 30 Dec 1992

    Location: /pub/msdos/SIMTEL20-mirror/info
      FILE      rw-r--r--    331544  Sep 15 06:55   inter32a.zip
      FILE      rw-r--r--    307988  Sep 15 06:56   inter32b.zip
      FILE      rw-r--r--    165049  Sep 15 06:56   inter32c.zip
    Location: /pub/msdos/databases/info
      FILE      rw-r--r--    331544  Sep 15 06:55   inter32a.zip
      FILE      rw-r--r--    307988  Sep 15 06:56   inter32b.zip
      FILE      rw-r--r--    165049  Sep 15 06:56   inter32c.zip


Host pinus.slu.se   (130.238.98.11)
Last updated 07:38 27 Sep 1992

    Location: /wuarchive.wustl.edu/archive/mirrors/msdos/info
      FILE      rw-r--r--    331544  Sep 14 00:00   inter32a.zip
      FILE      rw-r--r--    307988  Sep 14 00:00   inter32b.zip
      FILE      rw-r--r--    165049  Sep 14 00:00   inter32c.zip
    Location: /wuarchive.wustl.edu/archive/mirrors4/garbo.uwasa.fi/programming
      FILE      r--r--r--    331814  Sep 13 12:48   inter32a.zip
      FILE      r--r--r--    308258  Sep 13 12:50   inter32b.zip
      FILE      r--r--r--    165319  Sep 13 12:37   inter32c.zip

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Chris

--
     Beware of programmers who carry screwdrivers!