Sunday, December 14, 2014

Arduino: ColecoVision Cartridge Reader

With the numerous emulators and documentation on classic gaming consoles available today, it is easier than ever to create a “homebrew” video game for one of these classic game consoles (see http://en.wikipedia.org/wiki/Homebrew_(video_games) for more information about homebrew video games). Even though it is easier than it used to be, it can still be quite a challenge. It often helps to see how existing games work before creating a new one from scratch.

This article explains how to create a ColecoVision cartridge reader using an Arduino UNO (or similar product) and a PC.

What You Need

Note: If using an Arduino board with 29 or more digital I/O pins (e.g. the Arduino Due, Arduino MEGA ADK, Arduino Mega 2560, etc.), this can be built without using the two 8-bit shift registers (i.e. the 74HC595 or STP16C596).

ColecoVision Cartridge Overview

Fortune Builder Cartridge

ColecoVision cartridges typically come in sizes of 8K, 16K, 24K, or 32K. I have also encountered a few 12K cartridges. They generally have one to four 8K rom chips, although I have seen a few exceptions. For example, the Pitfall cartridge I own has a single 16K rom chip.

 

 

 

 

 

Inside Cartridge With Case

Image of the inside of the 24k Donkey Kong cartridge.

 

 

 

 

 

 

 

ColecoVision Cartridge Pin Outs

ColecoVision cartridges have 15 address pins, 8 data pins, 4 low-enabled chip select pins, 2 ground pins, and a Vcc pin. The layout of the 30 ColecoVision pins is shown below:

Cartridge Slot With Labels

Not Enough Pins

Arduino UNO R2 FrontThe Arduino UNO only has 20 pins that can be used for digital I/O. Two of these are used for the serial communication to the host PC, and I avoid using pin 13, since it is wired to the LED on the Arduino board. That leaves only 17 pins on the Arduino to connect to the 27 pins (15 address, 8 data, and 4 chip select) on the ColecoVision cartridge.

 

 

Shift Register Circuit

Shift Register Circuit DiagramIn order to reduce the number of Arduino pins required, a shift register circuit can be used that allows the Arduino to set the cartridge’s 15 address pins using only three Arduino pins. This circuit is described in detail on the Arduino website at http://arduino.cc/en/tutorial/ShiftOut. The LEDs and resistors shown in the example are not required for the cartridge reader, but I included them so I could see what the cartridge reader was doing.

 

 

 

Connections Table

From Pin To Pin
Cartridge Connector (A01) 9 74HC595 #1 1
Cartridge Connector (A02) 11 74HC595 #1 2
Cartridge Connector (A03) 15 74HC595 #1 3
Cartridge Connector (A04) 17 74HC595 #1 4
Cartridge Connector (A05) 21 74HC595 #1 5
Cartridge Connector (A06) 23 74HC595 #1 6
Cartridge Connector (A07) 25 74HC595 #1 7
Arduino GND 74HC595 #1 8
Arduino Vcc 74HC595 #1 10
Arduino 11 74HC595 #1 11
Arduino 12 74HC595 #1 12
Arduino GND 74HC595 #1 13
Arduino 10 74HC595 #1 14
Cartridge Connector (A00) 7 74HC595 #1 15
Arduino Vcc 74HC595 #1 16
Cartridge Connector (A09) 26 74HC595 #2 1
Cartridge Connector (A10) 16 74HC595 #2 2
Cartridge Connector (A11) 14 74HC595 #2 3
Cartridge Connector (A12) 24 74HC595 #2 4
Cartridge Connector (A13) 19 74HC595 #2 5
Cartridge Connector (A14) 20 74HC595 #2 6
Arduino GND 74HC595 #2 8
Arduino Vcc 74HC595 #2 10
Arduino 11 74HC595 #2 11
Arduino 12 74HC595 #2 12
Arduino GND 74HC595 #2 13
74HC595 #1 9 74HC595 #2 14
Cartridge Connector (A08) 28 74HC595 #2 15
Arduino Vcc 74HC595 #2 16

Chip Select Pins

The four chip select pins on the cartridge correspond to the four ROM chips that may be present in the cartridge. The first chip select pin (Chip Select 0x8000) should be toggled (high to low) when reading any addresses between 0x8000 and 0x9FFF. Likewise, Chip Select 0xA000 should be toggled for addresses between 0xA000 and 0xBFFF, Chip Select 0xC000 for 0xC000 through 0xDFFF, and Chip Select 0xE000 for 0xE000 through 0xFFFF.

From Pin To Pin
Arduino A0 Cartridge Connector (Chip Select 0x8000) 18
Arduino A1 Cartridge Connector (Chip Select 0xA000) 22
Arduino A2 Cartridge Connector (Chip Select 0xC000) 2
Arduino A3 Cartridge Connector (Chip Select 0xE000) 27

Data, Vcc, and Ground Pins

Once the address pins and chip select pins have been wired up, the data, Vcc, and ground pins of the cartridge can be connected to the Arduino.

From Pin To Pin
Arduino Vcc Cartridge Connector (Vcc) 30
Arduino GND Cartridge Connector (GND) 13, 29
Arduino 2 Cartridge Connector (Data 0) 5
Arduino 3 Cartridge Connector (Data 1) 3
Arduino 4 Cartridge Connector (Data 2) 1
Arduino 5 Cartridge Connector (Data 3) 4
Arduino 6 Cartridge Connector (Data 4) 6
Arduino 7 Cartridge Connector (Data 5) 8
Arduino 8 Cartridge Connector (Data 6) 10
Arduino 9 Cartridge Connector (Data 7) 12

Arduino Sketch File

The following Arduino Sketch file causes the Arduino to wait for a line from the host computer. If the line read in is “READ ALL”, the Arduino will do the following:

  • Send a “START:” line to the host computer.
  • Read all of the data from the cartridge and send it to the host computer in HEX, one byte per line.
  • Send a “:END” line to the host computer.

One the cartridge data has been sent to the host computer, the Arduino is ready for its next command from the host computer.

// ColecoVision / ADAM Cartridge Reader
// for the Arduino UNO
// 2014-11-25
//----------------------------------------------------------------------------------

// Arduino Pins
const int gcChipSelectLine[4] = { A0, A1, A2, A3 };
const int gcShiftRegisterClock = 11;
const int gcStorageRegisterClock = 12;
const int gcSerialAddress = 10;
const int gcDataBit[8] = { 2, 3, 4, 5, 6, 7, 8, 9 };

// Shifts a 16-bit value out to a shift register.
// Parameters:
// dataPin - Arduino Pin connected to the data pin of the shift register.
// clockPin - Arduino Pin connected to the data clock pin of the shift register.
//----------------------------------------------------------------------------------
void shiftOut16(int dataPin, int clockPin, int bitOrder, int value)
{
// Shift out highbyte for MSBFIRST
shiftOut(dataPin, clockPin, bitOrder, (bitOrder == MSBFIRST ? (value >> 8) : value));
// shift out lowbyte for MSBFIRST
shiftOut(dataPin, clockPin, bitOrder, (bitOrder == MSBFIRST ? value : (value >> 8)));
}

// Select which chip on the cartridge to read (LOW = Active).
// Use -1 to set all chip select lines HIGH.
//----------------------------------------------------------------------------------
void SelectChip(byte chipToSelect)
{
for(int currentChipLine = 0; currentChipLine < 4; currentChipLine++)
{
digitalWrite(gcChipSelectLine[currentChipLine], (chipToSelect != currentChipLine));
}
}

// Set Address Lines
//----------------------------------------------------------------------------------
void SetAddress(unsigned int address)
{
SelectChip(-1);

// Disable shift register output while loading address
digitalWrite(gcStorageRegisterClock, LOW);

// Write Out Address
shiftOut16(gcSerialAddress, gcShiftRegisterClock, MSBFIRST, address);

// Enable shift register output
digitalWrite(gcStorageRegisterClock, HIGH);

int chipToSelect;

if (address < 0xA000) {
chipToSelect = 0;
} else if (address < 0xC000) {
chipToSelect = 1;
} else if (address < 0xE000) {
chipToSelect = 2;
} else {
chipToSelect = 3;
}
SelectChip(chipToSelect);
}

// Read data lines
//----------------------------------------------------------------------------------
void ReadDataLines()
{
const char cHexLookup[16] = {
'0', '1', '2', '3', '4', '5', '6', '7',
'8', '9', 'A', 'B', 'C', 'D', 'E', 'F'};

int highNibble = 0;
int lowNibble = 0;
boolean dataBits[8];
char byteReadHex[4];

for(int currentBit = 0; currentBit < 8; currentBit++)
{
dataBits[currentBit] = digitalRead(gcDataBit[currentBit]);
}

highNibble = (dataBits[7] << 3) + (dataBits[6] << 2) + (dataBits[5] << 1) + dataBits[4];
lowNibble = (dataBits[3] << 3) + (dataBits[2] << 2) + (dataBits[1] << 1) + dataBits[0];

Serial.write(cHexLookup[highNibble]);
Serial.write(cHexLookup[lowNibble]);
Serial.println();
}

// Read all of the data from the cartridge.
//----------------------------------------------------------------------------------
void ReadCartridge()
{
unsigned int baseAddress = 0x8000;

Serial.println("START:");

// Read Current Chip (cartridge is 32K, each chip is 8k)
for (unsigned int currentAddress = 0; currentAddress < 0x8000; currentAddress++)
{
SetAddress(baseAddress + currentAddress);
ReadDataLines();
}

Serial.println(":END");
}

// Returns the next line from the serial port as a String.
//----------------------------------------------------------------------------------
String SerialReadLine()
{
const int BUFFER_SIZE = 81;
char lineBuffer[BUFFER_SIZE];
int currentPosition = 0;
int currentValue;

do
{
// Read until we get the next character
do
{
currentValue = Serial.read();
} while (currentValue == -1);

// ignore '\r' characters
if (currentValue != '\r')
{
lineBuffer[currentPosition] = currentValue;
currentPosition++;
}

} while ((currentValue != '\n') && (currentPosition < BUFFER_SIZE));
lineBuffer[currentPosition-1] = 0;

return String(lineBuffer);
}

// Indicate to remote computer Arduino is ready for next command.
//----------------------------------------------------------------------------------
void ReadyForCommand()
{
Serial.println("READY:");
}

void setup()
{
// Setup Serial Monitor
Serial.begin(57600);

// Setup Chip Select Pins
for(int chipLine = 0; chipLine < 4; chipLine++)
{
pinMode(gcChipSelectLine[chipLine], OUTPUT);
}

// Setup Serial Address Pins
pinMode(gcShiftRegisterClock, OUTPUT);
pinMode(gcStorageRegisterClock, OUTPUT);
pinMode(gcSerialAddress, OUTPUT);

// Setup Data Pins
for(int currentBit = 0; currentBit < 8; currentBit++)
{
pinMode(gcDataBit[currentBit], INPUT_PULLUP);
}

while (!Serial) {
; // wait for serial port to connect. Needed for Leonardo only.
}

// Reset Output Lines
SetAddress(0);

ReadyForCommand();
}

void loop()
{
if (Serial.available() > 0)
{
String lineRead = SerialReadLine();
lineRead.toUpperCase();

if (lineRead == "READ ALL")
{
ReadCartridge();
} // lineRead = "Read All"

ReadyForCommand();

} // Serial.available
}


If you are fortunate enough to be using an Arduino board with 29 or more digital I/O pins (e.g. the Arduino Due, Arduino MEGA ADK, Arduino Mega 2560, etc.) and you are not using the shift register circuit, the SetAddress function in the sketch file above will need to be re-written.

PC Software

Reading a CartridgeI wrote a little Windows application which can read the ColecoVision cartridge data sent by the Arduino, display it on the screen, and save it to a file.

The Windows executable and associated sketch file can be downloaded at ColecoVisionCartridgeReader.zip. The source code for the application and associated sketch file can be downloaded at ColecoVisionCartridgeReaderSource.zip.

After the program reads the contents of the cartridge from the Arduino, it truncates any 8K sections from the end of the cartridge that are blank (i.e. all bytes are set to FF).

Reading a Cartridge

Cartridge Reader with CartridgeOnce all of the circuits have been built and connected to the Arduino, the sketch file has been loaded onto the Arduino, and the ColecoVisionCartridgeReader.exe is installed on the host PC, a ColecoVision cartridge can be read.

 

 

 

 

Recommended steps to follow:

  1. Insert the cartridge into the connector.
  2. Plug the Arduino into the PC.
  3. Start the ColecoVisionCartridgeReader.exe application.
  4. Select File -> Read From Arduino from the main menu.
  5. Verify the settings are correct and click the Read button.

The progress dialog should appear and within 30 seconds the contents of the cartridge should appear on the screen.

Observations

The first two bytes of all ColecoVision cartridges are 55 and AA. If the AA comes first, the cartridge displays the standard ColecoVision title screen (e.g. standard ColecoVision cartridges like Donkey Kong, Mouse Trap, Zaxxon, etc.). If the 55 comes first, the cartridge skips the standard title screen (e.g. third-party cartridges like Q*Bert, Frogger, Pitfall, etc.).


Interesting Cartridges to Read


Cartridge Reader with Donkey Kong Loaded

Almost everyone who owns a ColecoVision has a Donkey Kong cartridge, since it came with the game console. There are at least two different versions of this cartridge in circulation. The first edition of this cartridge was 24K, but the second edition was only 16K. Using the Arduino ColecoVision Cartridge reader, you can determine which edition you have. Another way to tell is to look at Pauline’s umbrella on the second and third levels of the game. In the 24K version of the cartridge, the umbrella has a glitch shown in the following screenshot, but the updated 16K version of the cartridge does not.

24k Version => Donkey Kong Umbrella 24k   Donkey Kong Umbrella 16k <= 16k Version

Another interesting cartridge to look at is Fortune Builder. It is one of the few 32K cartridges. It also has a large number of text strings, which can be interesting to read through.

Cartridge Reader with Fortune Builder Loaded

Possible Future Enhancements

  • Detect 12K cartridges and truncate the duplicate 4K at the end of the cartridge image.
  • Have the Arduino check the first two bytes of the cartridge to verify they are correct before reading the entire cartridge.
  • Speed up the transfer of the cartridge data by sending multiple bytes on the same line.