//address pins (note - cartridge interface starts at A1 so A[0] == A1, A[1] == A2 etc)
int A[23] = {27,29,31,33,35,37,39,41,44,42,40,38,36,34,32,30,28,43,45,47,49,51,53};

//data pins
int D[16] = {23,22,2,16,17,14,24,25,26,21,3,15, 52,50,48,46};

void resetAddressBus(){
  for(byte i=0; i<23; i++){
    pinMode(A[i], OUTPUT);
    digitalWrite(A[i], LOW);
  }  
}

void writeAddress(long addr){
  long mask = 1;
  for(int i=0; i<23; i++){
    long test = (mask & addr) >> i;
    if(test == 1){
      digitalWrite(A[i], HIGH);
    }else{
      digitalWrite(A[i], LOW);
    }
    mask = mask << 1;
  }  
}

word readData(){
  word d = 0;
  word mask2 = 0b1;
  for(int i=0; i<16; i++){
    int b = digitalRead(D[i]);
    
    if(b == HIGH){
      d = d | mask2;
    } 
    mask2 = mask2 << 1;
  }
  return d;
}

void setup(){
  Serial.begin(9600);
  //Serial.println("setup()");
  resetAddressBus();
  for(int i=0; i<16; i++){
    pinMode(D[i], INPUT);
  }
  
  Serial1.begin(9600);
  Serial1.print(0xFE, BYTE);
  Serial1.print(0x01, BYTE);
  Serial1.print(0xFE, BYTE);
  Serial1.print(0x80, BYTE);
}

long a = 0x80; // 0x100 start of 'SEGA'

byte lcd[16] = { ' ',' ',' ',' ',' ',' ',' ',' ',' ',' ',' ',' ',' ',' ',' ',' ' };
byte lcdcur = 0;

void loop(){
  //write a to the address bus
  writeAddress(a);
  delay(250);
  
  //read the data bus
  word d = readData();
  //convert the 16 bit word to two bytes
  byte d2 = d & 0xFF;
  byte d1 = (d & 0xFF00) >> 8;
  
  if(d1 != 0){
    Serial.print(d1);
    lcd[16-2] = d1;
  }

  lcdcur++;
  
  if(d2 != 0){
    Serial.print(d2);

    lcd[16-1] = d2;
  }

  Serial1.print(0xFE, BYTE);
  Serial1.print(0x80, BYTE);
  
  
  //write to lcd
  for(byte i=0; i<16; i++){
    Serial1.print(lcd[i]);
  }
  
  //shuffle down two
  for(byte i=0; i<(16-2); i++){
    lcd[i] = lcd[i+2];
  }
  
  lcdcur++;
  if(lcdcur == 16){
    lcdcur = 0;
  }
  
  a++;
  //loop back to start when we hit a null
  if((d1 == 0) || (d2 == 0)){
    a = 0x80;
  }
}