NOTICE: This research and implementation in this post is not 100% correct. Please check out my SegaController Arduino library for better code and How To Read Sega Controllers for details on how it works.

Version 1.0

A couple of months ago I detailed the process by which I used an Arduino Uno to read the button presses of a pair of Sega Genesis controllers. It was my first bit of micro-controller programming, and it has exposed me to a whole new world of possibilities for hardware hacking. So it is with some certain future projects in mind that I’ve revisited and updated that initial code.

Version 1.1

Other than some minor code cleanup, the only major feature-add to the core of the sketch is to support reading the “Mode” button on six-button controllers (thanks to a comment from soe for that). The other change, now that I’ve acquired an Arduino Leonardo, is to create a fork of the sketch which reports the button presses as keyboard key presses via the ATmega32u4 chip’s ability appear as a USB keyboard.

Anyway, here’s the updated code (for reporting over the Serial connection):

/*
 * Sega Controller Reader
 * Author: Jon Thysell <thysell@gmail.com>
 * Version: 1.1
 * Date: 9/29/2014
 *
 * Reads buttons presses from Sega Genesis 3/6 button controllers
 * and reports their state via the Serial connection. Handles hot
 * swapping of controllers and auto-switches between 3 and 6 button
 * polling patterns.
 *
 */

const int PLAYERS = 2;

// Controller Button Flags
const int ON = 1;
const int UP = 2;
const int DOWN = 4;
const int LEFT = 8;
const int RIGHT = 16;
const int START = 32;
const int A = 64;
const int B = 128;
const int C = 256;
const int X = 512;
const int Y = 1024;
const int Z = 2048;
const int MODE = 4096;

// Controller DB9 Pin 7 Mappings
const int SELECT[] = { 8, 9 };

typedef struct
{
  int player;
  int pin;
  int lowFlag;
  int highFlag;
  int pulse3Flag;
} input;

// Controller DB9 Pin to Button Flag Mappings
// First column is the controller index, second column
// is the Arduino pin that the controller's DB9 pin is
// attached to, remaing columns are the button flags
input inputMap[] = {
  { 0,  2,  UP,    UP,     Z    }, // P0 DB9 Pin 1
  { 0,  3,  DOWN,  DOWN,   Y    }, // P0 DB9 Pin 2
  { 0,  4,  ON,    LEFT,   X    }, // P0 DB9 Pin 3
  { 0,  5,  ON,    RIGHT,  MODE }, // P0 DB9 Pin 4
  { 0,  6,  A,     B,      0    }, // P0 DB9 Pin 6
  { 0,  7,  START, C,      0    }, // P0 DB9 Pin 9
  { 1,  A0, UP,    UP,     Z    }, // P1 DB9 Pin 1
  { 1,  A1, DOWN,  DOWN,   Y    }, // P1 DB9 Pin 2
  { 1,  A2, ON,    LEFT,   X    }, // P1 DB9 Pin 3
  { 1,  A3, ON,    RIGHT,  MODE }, // P1 DB9 Pin 4
  { 1,  A4, A,     B,      0    }, // P1 DB9 Pin 6
  { 1,  A5, START, C,      0    }  // P1 DB9 Pin 9
};

// Controller State
int currentState[] = { 0, 0 };
int lastState[] = { -1, -1 };

// Default to three-button mode until six-button connects
boolean sixButtonMode[] = { false, false };

void setup()
{
  // Setup input pins
  for (int i = 0; i < sizeof(inputMap) / sizeof(input); i++)
  {
    pinMode(inputMap[i].pin, INPUT);
    digitalWrite(inputMap[i].pin, HIGH);
  }

  // Setup select pins
  for (int i = 0; i < PLAYERS; i++)
  {
    pinMode(SELECT[i], OUTPUT);
    digitalWrite(SELECT[i], HIGH);
  }

  Serial.begin(9600);
}

void loop()
{
  readButtons();
  sendStates();
}

void readButtons()
{
  for (int i = 0; i < PLAYERS; i++)
  {
    resetState(i);
    if (sixButtonMode[i])
    {
      read6buttons(i);
    }
    else
    {
      read3buttons(i);
    }
  }
}

void resetState(int player)
{
  currentState[player] = 0;
}

void read3buttons(int player)
{
  // Set SELECT LOW and read lowFlag
  digitalWrite(SELECT[player], LOW);

  delayMicroseconds(20);

  for (int i = 0; i < sizeof(inputMap) / sizeof(input); i++)
  {
    if (inputMap[i].player == player && digitalRead(inputMap[i].pin) == LOW)
    {
      currentState[player] |= inputMap[i].lowFlag;
    }
  }

  // Set SELECT HIGH and read highFlag
  digitalWrite(SELECT[player], HIGH);

  delayMicroseconds(20);

  for (int i = 0; i < sizeof(inputMap) / sizeof(input); i++)
  {
    if (inputMap[i].player == player && digitalRead(inputMap[i].pin) == LOW)
    {
      currentState[player] |= inputMap[i].highFlag;
    }
  }

  // When a six-button first connects, it'll spam UP and DOWN,
  // which signals the game to switch to 6-button polling
  if (currentState[player] == (ON | UP | DOWN))
  {
    sixButtonMode[player] = true;
  }
  // When a controller disconnects, revert to three-button polling
  else if ((currentState[player] & ON) == 0)
  {
    sixButtonMode[player] = false;
  }

  delayMicroseconds(20);
}

void read6buttons(int player)
{
  // Poll for three-button states twice
  read3buttons(player);
  read3buttons(player);

  // After two three-button polls, pulse the SELECT line
  // so the six-button reports the higher button states
  digitalWrite(SELECT[player], LOW);
  delayMicroseconds(20);
  digitalWrite(SELECT[player], HIGH);

  for(int i = 0; i < sizeof(inputMap) / sizeof(input); i++)
  {
    if (inputMap[i].player == player && digitalRead(inputMap[i].pin) == LOW)
    {
      currentState[player] |= inputMap[i].pulse3Flag;
    }
  }

  delayMicroseconds(1000);
}

void sendStates()
{
  // Only report controller states if at least one has changed
  boolean hasChanged = false;

  for (int i = 0; i < PLAYERS; i++)
  {
    if (currentState[i] != lastState[i])
    {
      hasChanged = true;
    }
  }

  if (hasChanged)
  {
    for (int i = 0; i < PLAYERS; i++)
    {
      Serial.print((currentState[i] & ON) == ON ? "+" : "-");
      Serial.print((currentState[i] & UP) == UP ? "U" : "0");
      Serial.print((currentState[i] & DOWN) == DOWN ? "D" : "0");
      Serial.print((currentState[i] & LEFT) == LEFT ? "L" : "0");
      Serial.print((currentState[i] & RIGHT) == RIGHT ? "R" : "0");
      Serial.print((currentState[i] & START) == START ? "S" : "0");
      Serial.print((currentState[i] & A) == A ? "A" : "0");
      Serial.print((currentState[i] & B) == B ? "B" : "0");
      Serial.print((currentState[i] & C) == C ? "C" : "0");
      Serial.print((currentState[i] & X) == X ? "X" : "0");
      Serial.print((currentState[i] & Y) == Y ? "Y" : "0");
      Serial.print((currentState[i] & Z) == Z ? "Z" : "0");
      Serial.print((currentState[i] & MODE) == MODE ? "M" : "0");

      Serial.print((i == 0) ? "," : "\n");
      lastState[i] = currentState[i];
    }
  }
}

As with the previous version, all you have to do is upload the sketch and connect the controller’s DB9 pins to the Arduino following the mapping in inputMap in the code.

Now, if you have an Arduino Leonardo (or compatible board), and want the controller button presses to map to keyboard keys instead, you can upload the following sketch:

/*
 * Sega Controller Reader (Keyboard)
 * Author: Jon Thysell <thysell@gmail.com>
 * Version: 1.1
 * Date: 9/29/2014
 *
 * Reads buttons presses from Sega Genesis 3/6 button controllers
 * and reports their state via keyboard button presses. Handles hot
 * swapping of controllers and auto-switches between 3 and 6 button
 * polling patterns.
 *
 */

const int PLAYERS = 2;

// Controller Button Flags
const int ON = 1;
const int UP = 2;
const int DOWN = 4;
const int LEFT = 8;
const int RIGHT = 16;
const int START = 32;
const int A = 64;
const int B = 128;
const int C = 256;
const int X = 512;
const int Y = 1024;
const int Z = 2048;
const int MODE = 4096;

// Controller DB9 Pin 7 Mappings
const int SELECT[] = { 8, 9 };

typedef struct
{
  int player;
  int pin;
  int lowFlag;
  int highFlag;
  int pulse3Flag;
} input;

// Controller DB9 Pin to Button Flag Mappings
// First column is the controller index, second column
// is the Arduino pin that the controller's DB9 pin is
// attached to
input inputMap[] = {
  { 0,  2,  UP,    UP,     Z    }, // P0 DB9 Pin 1
  { 0,  3,  DOWN,  DOWN,   Y    }, // P0 DB9 Pin 2
  { 0,  4,  ON,    LEFT,   X    }, // P0 DB9 Pin 3
  { 0,  5,  ON,    RIGHT,  MODE }, // P0 DB9 Pin 4
  { 0,  6,  A,     B,      0    }, // P0 DB9 Pin 6
  { 0,  7,  START, C,      0    }, // P0 DB9 Pin 9
  { 1,  A0, UP,    UP,     Z    }, // P1 DB9 Pin 1
  { 1,  A1, DOWN,  DOWN,   Y    }, // P1 DB9 Pin 2
  { 1,  A2, ON,    LEFT,   X    }, // P1 DB9 Pin 3
  { 1,  A3, ON,    RIGHT,  MODE }, // P1 DB9 Pin 4
  { 1,  A4, A,     B,      0    }, // P1 DB9 Pin 6
  { 1,  A5, START, C,      0    }  // P1 DB9 Pin 9
};

typedef struct
{
  int player;
  int flag;
  char key;
} output;

// Controller Button Flag to Keyboard Mappings
// First column is the controller index, second column
// is the button flag, third is keyboard key
output outputMap[] = {
  { 0, UP,    KEY_UP_ARROW },
  { 0, DOWN,  KEY_DOWN_ARROW },
  { 0, LEFT,  KEY_LEFT_ARROW },
  { 0, RIGHT, KEY_RIGHT_ARROW },
  { 0, START, KEY_RETURN },
  { 0, A,     'z' },
  { 0, B,     'x' },
  { 0, C,     'c' },
  { 0, X,     'a' },
  { 0, Y,     's' },
  { 0, Z,     'd' },
  { 0, MODE,  'q' },
  { 1, UP,    'i' },
  { 1, DOWN,  'k' },
  { 1, LEFT,  'j' },
  { 1, RIGHT, 'l' },
  { 1, START, 't' },
  { 1, A,     'v' },
  { 1, B,     'b' },
  { 1, C,     'n' },
  { 1, X,     'f' },
  { 1, Y,     'g' },
  { 1, Z,     'h' },
  { 1, MODE,  'r' }
};

// Controller State
int currentState[] = { 0, 0 };
int lastState[] = { -1, -1 };

// Default to three-button mode until six-button connects
boolean sixButtonMode[] = { false, false };

void setup()
{
  // Setup input pins
  for (int i = 0; i < sizeof(inputMap) / sizeof(input); i++)
  {
    pinMode(inputMap[i].pin, INPUT);
    digitalWrite(inputMap[i].pin, HIGH);
  }

  // Setup select pins
  for (int i = 0; i < PLAYERS; i++)
  {
    pinMode(SELECT[i], OUTPUT);
    digitalWrite(SELECT[i], HIGH);
  }

  Keyboard.begin();
}

void loop()
{
  readButtons();
  sendStates();
}

void readButtons()
{
  for (int i = 0; i < PLAYERS; i++)
  {
    resetState(i);
    if (sixButtonMode[i])
    {
      read6buttons(i);
    }
    else
    {
      read3buttons(i);
    }
  }
}

void resetState(int player)
{
  currentState[player] = 0;
}

void read3buttons(int player)
{
  // Set SELECT LOW and read lowFlag
  digitalWrite(SELECT[player], LOW);

  delayMicroseconds(20);

  for (int i = 0; i < sizeof(inputMap) / sizeof(input); i++)
  {
    if (inputMap[i].player == player && digitalRead(inputMap[i].pin) == LOW)
    {
      currentState[player] |= inputMap[i].lowFlag;
    }
  }

  // Set SELECT HIGH and read highFlag
  digitalWrite(SELECT[player], HIGH);

  delayMicroseconds(20);

  for (int i = 0; i < sizeof(inputMap) / sizeof(input); i++)
  {
    if (inputMap[i].player == player && digitalRead(inputMap[i].pin) == LOW)
    {
      currentState[player] |= inputMap[i].highFlag;
    }
  }

  // When a six-button first connects, it'll spam UP and DOWN,
  // which signals the game to switch to 6-button polling
  if (currentState[player] == (ON | UP | DOWN))
  {
    sixButtonMode[player] = true;
  }
  // When a controller disconnects, revert to three-button polling
  else if ((currentState[player] & ON) == 0)
  {
    sixButtonMode[player] = false;
  }

  delayMicroseconds(20);
}

void read6buttons(int player)
{
  // Poll for three-button states twice
  read3buttons(player);
  read3buttons(player);

  // After two three-button polls, pulse the SELECT line
  // so the six-button reports the higher button states
  digitalWrite(SELECT[player], LOW);
  delayMicroseconds(20);
  digitalWrite(SELECT[player], HIGH);

  for(int i = 0; i < sizeof(inputMap) / sizeof(input); i++)
  {
    if (inputMap[i].player == player && digitalRead(inputMap[i].pin) == LOW)
    {
      currentState[player] |= inputMap[i].pulse3Flag;
    }
  }

  delayMicroseconds(1000);
}

void sendStates()
{
  for (int i = 0; i < sizeof(outputMap) / sizeof(output); i++)
  {
    int last = (lastState[outputMap[i].player] & outputMap[i].flag);
    int current = (currentState[outputMap[i].player] & outputMap[i].flag);

    if (last != current)
    {
      if (current == outputMap[i].flag)
      {
        Keyboard.press(outputMap[i].key);
      }
      else
      {
        Keyboard.release(outputMap[i].key);
      }
    }
  }

  for (int i = 0; i < PLAYERS; i++)
  {
    lastState[i] = currentState[i];
  }
}

If you want to change the button to key mapping, simply update outputMap in the code. You can use any key on the keyboard, including special keys and modifiers.

I hope this is a worthy updated to the sketch – it was a great delight to test it by playing emulated games on my laptop with real Genesis controllers. It worked wonderfully, and I can’t wait to get this integrated into a bigger project.

So happy hacking and stay tuned for more!

/jon

Update 26-JUN-2017: The source is now available on GitHub here.

Update 28-JUN-2017: I’ve announced a newer, stable, reusable version at Introducing the SegaController Arduino library.