Introduction

Design

Connector: Female DB9

     5 4 3 2 1

       9 8 7 6
 

Pin	Description
1	Joystick 0 (up)
2	Joystick 1 (down)
3	Joystick 2 (left)
4	Joystick 3 (right)
5	Not Used
6	Button 1 (fire)
7	Not Used
8	Ground
9	Not Used

To get the Atari controller to work with the Altera UP1 board, the controller has to produce a logic '0' (0V) when pressed and logic '1' (5V) when not pressed. As seen from the pin layout, the controller does not have a Vcc input, therefore it cannot produce logic '1'. A external circuit has to be built so that the controller can produce logic '1'. An example of the Atari controller internal circuit is shown below:

Gnd (Pin8)        Joystick 0 (up)                Pin 1
    o--------------------- \-----------------o (to UP1 board)

From the diagram, we realize that we have to built another external to produce +5V for logic '1' to the UP1 board. The external circuit is to produce +5V at pin 1 when the internal circuit is opened. And produce 0V when the internal is shorted. A huge resistor is need to drain most of the voltage when the internal circuit is shorted to produce 0V. The whole circuit is given below.

Gnd (Pin8)        Joystick 0 (up)                 Pin 1            5.6K Ohm        Vcc
    o--------------------- \-----------------o--------------/\/\/\-----------o

When the joystick 0 switch is closed, pin 1 is ground therefore produces logic '0' (0V). When the joystick 0 is opened, pin 1 produces logic '1' (5V) due to the open circuit. The rest of the pins are connected to their own external circuit except the Gnd pin and to the UP1 FLEX_EXPAN_A connectors. The following table is the pin assignments on the FLEX_EXPAN_A:
 

Pin	Hole Number	FLEX_EXPAN_A Pin Assignment
1	15	45
2	17	48
3	19	50
4	21	53
6	23	55
8	4/6	GND

This application only applies to Atari ST controller. If there is other DB9 controller, refer to http://www.phm.lu/documentation/connectors/Control%20DB9.asp for the DB9 pin layout .

Test Program

The outputs from the code are display on FLEX_DIGIT to valid the test. We assign the output as followed:

Please refer to figure 4 on page 9 in the UP1 documentation for the LED segment layout.
 

Output Name	LED segment	FLEX_DIGIT Pin Assignment
o_up	a	6
o_down	g	13
o_left	b	7
o_right	f	12
o_button	Decimal Point	14

A potential problem with all controller is the deboucing on the button. During testing, the debounce of the controller doesn't exceed 20% of the value change. This will not create problems when using the controller.

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