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Apple II NES/SNES Joypad Interface Page


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12/20/98 

Interface Description: 
   The interface is just a bunch of wires and connectors. There are no 
chips and no circuit boards! Also, if you follow my design the interface 
will work on an IBM PC with the popular SNESKEY. 

Warning: 
   It has been brought to my attention that the pre Apple IIgs machines 
use the keyboard to simulate joystick buttons. This combination has the 
potential to interrupt the NES pad communication at the least and burn 
it up at the worst. This interface was designed for the Apple IIgs, so 
using it on earlier machines at your own risk. 

Apple II Joystick Interface Block Diagram: 
Block Diagram 

Internal Apple II Joystick Interface Pinout: 
Pinout 

NES Connector Pinout: 
Pinout 

What wires go where: 

Apple II Joystick Connector to 25 Pin D-Sub Connector Female: 

Joystick Connector               25 Pin D-Sub Female 
AN0 Pin 15                            Pin 2 
AN1 Pin 14                            Pin 3 
PB0 Pin 2                             Pin 10 
PB1 Pin 3                             Pin 12 
+5V Pin 1                             Pins 7,8,9 
GND Pin 8                             Pin 19 

25 Pin D-Sub Connector Male to NES Joypad: 

25 Pin D-Sub Connector Male               NES Joypads 
Pin 2                                     Pin 2 CLK 
Pin 3                                     Pin 3 LATCH 
Pin 10                                    Pin 4 Pad 0 
Pin 12                                    Pin 4 Pad 1 
Pin 7                                     Pin 5 +5V 
Pin 19                                    Pin 1 GND 

Note: You could go directly from the Joystick Connector to the NES 
Joypads. However, you would lose PC compatibility and would have to open 
your computer everytime you wanted to disconnect the Joypads. 

Programming: 

The NES joypad is based upon a single 4021 CMOS chip. It is simply a 
parallel to serial chip. In order to get data from it 
you have to LATCH the data from the buttons into the chip. Then CLK 
(clock) in the bits. 

Bit 0 is button A 
Bit 1 is button B 
Bit 2 is button SELECT 
Bit 3 is button START 
Bit 4 is arrow UP 
Bit 5 is arrow DOWN 
Bit 6 is arrow LEFT 
Bit 7 is arrow RIGHT 

Here is some sample code is Applesoft BASIC: 

20 Z=PEEK(49240) 
40 Z=PEEK(49242) 
60 PRINT A$ 
80 LET A$ = "" 
100 Z=PEEK(49243) 
120 Z=PEEK(49242) 
140 B0=PEEK(49249) 
160 IF B0>127 THEN LET A$=A$ + "1" 
180 IF B0<=127 THEN LET A$=A$ + "0" 
200 Z=PEEK(49241) 
220 Z=PEEK(49240) 
240 LET L0=LEN(A$) 
260 IF L0>=8 THEN GOTO 60 
280 GOTO 140 

This code will output all 1's if no buttons have been pressed. If a 
button has been pressed then the corresponding 1 changes to a 0. Study 
the code. Convert it to assembly if you want. Have Fun. : ) Note: This 
code only reads joypad 0. You will have to add code to read joypad 1. 
 

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For Questions or Comments:
 frankc@cyberhighway.net