/*
 *  6502 assembler and emulator in Javascript
 *  (C)2006-2007 Stian Soreng - www.6502asm.com
 *
 *  Released under the GNU General Public License
 *  see http://gnu.org/licenses/gpl.html
 *
 */

var MAX_MEM = ((32*32)-1);
var codeCompiledOK = false;
var regA = 0;
var regX = 0;
var regY = 0;
var regP = 0;
var regPC = 0x600;
var regSP = 0x100;
var memory = new Array( 0x600 );
var runForever = false;
var labelIndex = new Array();
var labelPtr = 0;
var codeRunning = false;
var xmlhttp;
var myInterval;
var display = new Array( 0x400 );
var defaultCodePC = 0x600;
var palette = new Array(
  "#000000", "#ffffff", "#880000", "#aaffee",
  "#cc44cc", "#00cc55", "#0000aa", "#eeee77",
  "#dd8855", "#664400", "#ff7777", "#333333",
  "#777777", "#aaff66", "#0088ff", "#bbbbbb" );

var Opcodes = new Array(

    /* Name, Imm,  ZP,   ZPX,  ZPY,  ABS,  ABSX, ABSY, INDX, INDY, SNGL, BRA */

Array("ADC", 0x69, 0x65, 0x75, 0x00, 0x6d, 0x7d, 0x79, 0x61, 0x71, 0x00, 0x00),
Array("AND", 0x29, 0x25, 0x35, 0x31, 0x2d, 0x3d, 0x39, 0x21, 0x00, 0x00, 0x00),
Array("ASL", 0x00, 0x06, 0x16, 0x00, 0x0e, 0x1e, 0x00, 0x00, 0x00, 0x0a, 0x00),
Array("BIT", 0x00, 0x24, 0x00, 0x00, 0x2c, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00),
Array("BPL", 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x10),
Array("BMI", 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x30),
Array("BVC", 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x50),
Array("BVS", 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x70),
Array("BCC", 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x90),
Array("BCS", 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0xb0),
Array("BNE", 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0xd0),
Array("BEQ", 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0xf0),
Array("CMP", 0xc9, 0xc5, 0xd5, 0x00, 0xcd, 0xdd, 0xd9, 0xc1, 0xd1, 0x00, 0x00),
Array("CPX", 0xe0, 0xe4, 0x00, 0x00, 0xec, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00),
Array("CPY", 0xc0, 0xc4, 0x00, 0x00, 0xcc, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00),
Array("DEC", 0x00, 0xc6, 0xd6, 0x00, 0xce, 0xde, 0x00, 0x00, 0x00, 0x00, 0x00),
Array("EOR", 0x49, 0x45, 0x55, 0x00, 0x4d, 0x5d, 0x59, 0x41, 0x51, 0x00, 0x00),
Array("CLC", 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x18, 0x00),
Array("SEC", 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x38, 0x00),
Array("CLI", 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x58, 0x00),
Array("SEI", 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x78, 0x00),
Array("CLV", 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0xb8, 0x00),
Array("CLD", 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0xd8, 0x00),
Array("SED", 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0xf8, 0x00),
Array("INC", 0x00, 0xe6, 0xf6, 0x00, 0xee, 0xfe, 0x00, 0x00, 0x00, 0x00, 0x00),
Array("JMP", 0x00, 0x00, 0x00, 0x00, 0x4c, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00),
Array("JSR", 0x00, 0x00, 0x00, 0x00, 0x20, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00),
Array("LDA", 0xa9, 0xa5, 0xb5, 0x00, 0xad, 0xbd, 0xb9, 0xa1, 0xb1, 0x00, 0x00),
Array("LDX", 0xa2, 0xa6, 0x00, 0xb6, 0xae, 0x00, 0xbe, 0x00, 0x00, 0x00, 0x00),
Array("LDY", 0xa0, 0xa4, 0xb4, 0x00, 0xac, 0xbc, 0x00, 0x00, 0x00, 0x00, 0x00),
Array("LSR", 0x00, 0x46, 0x56, 0x00, 0x4e, 0x5e, 0x00, 0x00, 0x00, 0x4a, 0x00),
Array("NOP", 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0xea, 0x00),
Array("ORA", 0x09, 0x05, 0x15, 0x00, 0x0d, 0x1d, 0x19, 0x01, 0x11, 0x00, 0x00),
Array("TAX", 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0xaa, 0x00),
Array("TXA", 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x8a, 0x00),
Array("DEX", 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0xca, 0x00),
Array("INX", 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0xe8, 0x00),
Array("TAY", 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0xa8, 0x00),
Array("TYA", 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x98, 0x00),
Array("DEY", 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x88, 0x00),
Array("INY", 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0xc8, 0x00),
Array("ROR", 0x00, 0x66, 0x76, 0x00, 0x6e, 0x7e, 0x00, 0x00, 0x00, 0x6a, 0x00),
Array("ROL", 0x00, 0x26, 0x36, 0x00, 0x2e, 0x3e, 0x00, 0x00, 0x00, 0x2a, 0x00),
Array("RTI", 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x40, 0x00),
Array("RTS", 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x60, 0x00),
Array("SBC", 0xe9, 0xe5, 0xf5, 0x00, 0xed, 0xfd, 0xf9, 0xe1, 0xf1, 0x00, 0x00),
Array("STA", 0x00, 0x85, 0x95, 0x00, 0x8d, 0x9d, 0x99, 0x81, 0x91, 0x00, 0x00),
Array("TXS", 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x9a, 0x00),
Array("TSX", 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0xba, 0x00),
Array("PHA", 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x48, 0x00),
Array("PLA", 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x68, 0x00),
Array("PHP", 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x08, 0x00),
Array("PLP", 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x28, 0x00),
Array("STX", 0x00, 0x86, 0x00, 0x96, 0x8e, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00),
Array("STY", 0x00, 0x84, 0x94, 0x00, 0x8c, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00),
Array("---", 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00)
);

// Initialize everything.

document.getElementById( "compileButton" ).disabled = false;
document.getElementById( "runButton" ).disabled = true;
document.getElementById( "hexdumpButton" ).disabled = true;
document.getElementById( "fileSelect" ).disabled = false;

document.addEventListener( "keypress", keyPress, true );

// Paint the "display"

html = '<table class="screen">';
for( y=0; y<32; y++ ) {
  html += "<tr>";
  for( x=0; x<32; x++ ) {
    html += '<td class="screen" id="x' + x + 'y' + y + '"></td>';
  }
  html += "</tr>";
}
html += "</table>";
document.getElementById( "screen" ).innerHTML = html;

// Reset everything

reset();

/*
 *  keyPress() - Store keycode in ZP $ff
 *
 */

function keyPress( e ) {
  if( typeof window.event != "undefined" )
    e = window.event; // IE fix
  if( e.type == "keypress" ) {
    value = e.which;
    memStoreByte( 0xff, value );
  }
}


/*
 *  disableButtons() - Disables the Run and Debug buttons when text is
 *                     altered in the code editor
 *
 */

function disableButtons() {
  document.getElementById( "runButton" ).disabled = true;
  document.getElementById( "hexdumpButton" ).disabled = true;
  document.getElementById( "fileSelect" ).disabled = false;
  document.getElementById( "compileButton" ).disabled = false;
  document.getElementById( "runButton" ).value = "Run";
  codeCompiledOK = false;
  codeRunning = false;
  document.getElementById( "code" ).focus();
}

/*
 *  Load() - Loads a file from server
 *
 */

function Load( file ) {
  reset();
  disableButtons();
  document.getElementById( "code" ).value = "Loading, please wait..";
  document.getElementById( "compileButton" ).disabled = true;
  xmlhttp = new XMLHttpRequest();
  xmlhttp.onreadystatechange = FileLoaded;
  xmlhttp.open( "GET", "examples/" + file );
  xmlhttp.send( null );
}

function FileLoaded() {
  if( xmlhttp.readyState == 4 )
    if( xmlhttp.status == 200 ) {
      document.getElementById( "code" ).value = xmlhttp.responseText;
      document.getElementById( "compileButton" ).disabled = false;
    }
}

/*
 *  reset() - Reset CPU and memory.
 *
 */

function reset() {
  for( y=0; y<32; y++ )
    for( x=0; x<32; x++ ) {
      display[y*32+x] = document.getElementById( "x"+x+"y"+y ).style;
      display[y*32+x].background = "#000000";
    }
  for( x=0; x<0x600; x++ )  // clear ZP, stack and screen
    memory[x] = 0x00;
  regA = regX = regY = 0;
  defaultCodePC = regPC = 0x600;
  regSP = 0x100;
  regP = 0x20;
  runForever = false;
}


/*
 *  message() - Prints text in the message window
 *
 */

function message( text ) {
  obj = document.getElementById( "messages" );
  obj.innerHTML += text + "<br />";
  obj.scrollTop = obj.scrollHeight;
}

/*
 *  compileCode()
 * 
 *  "Compiles" the code into a string (global var compiledCode)
 * 
 */

function compileCode() {
  reset();
  document.getElementById( "messages" ).innerHTML = "";

  var code = document.getElementById( "code" ).value;
  code += "\n\n";
  lines = code.split( "\n" );
  codeCompiledOK = true;
  labelIndex = new Array();
  labelPtr = 0;

  message( "Indexing labels.." );

  defaultCodePC = regPC = 0x600;

  for( xc=0; xc<lines.length; xc++ ) {
    if( ! indexLabels( lines[xc] ) ) {
      message( "<b>Label already defined at line "+(xc+1)+":</b> "+lines[xc] );
      return false;
    }
  }

  str = "Found " + labelIndex.length + " label";
  if( labelIndex.length != 1 ) str += "s";
  message( str + "." );

  defaultCodePC = regPC = 0x600;
  message( "Compiling code.." );

  for( x=0; x<lines.length; x++ ) {
    if( ! compileLine( lines[x], x ) ) {
      codeCompiledOK = false;
      break;
    }
  }

  if( codeLen == 0 ) {
    codeCompiledOK = false;
    message( "No code to run." );
  }

  if( codeCompiledOK ) {
    document.getElementById( "runButton" ).disabled = false;
    document.getElementById( "hexdumpButton" ).disabled = false;
    document.getElementById( "compileButton" ).disabled = true;
    document.getElementById( "fileSelect" ).disabled = false;
    memory[defaultCodePC] = 0x00;
  } else {
    str = lines[x].replace( "<", "&lt;" ).replace( ">", "&gt;" );
    message( "<b>Syntax error line " + (x+1) + ": " + str + "</b>");
    document.getElementById( "runButton" ).disabled = true;
    document.getElementById( "compileButton" ).disabled = false;
    document.getElementById( "fileSelect" ).disabled = false;
    return;
  }

  message( "Code compiled successfully, " + codeLen + " bytes." );
}

/*
 *  indexLabels() - Pushes all labels to array.
 *
 */

function indexLabels( input ) {

  // remove comments

  input = input.replace( new RegExp( /^(.*?);.*/ ), "$1" );

  // trim line

  input = input.replace( new RegExp( /^\s+/ ), "" );
  input = input.replace( new RegExp( /\s+$/ ), "" );

  // Figure out how many bytes this instuction takes

  thisPC = defaultCodePC;

  codeLen = 0;
//  defaultCodePC = 0x600;
  compileLine( input );
  regPC += codeLen;

  // Find command or label

  if( input.match( new RegExp( /^\w+:/ ) ) ) {
    label = input.replace( new RegExp( /(^\w+):.*$/ ), "$1" );
    return pushLabel( label + "|" + thisPC );
  }
  return true;
}

/*
 *  pushLabel() - Push label to array. Return false if label already exists.
 * 
 */

function pushLabel( name ) {
  if( findLabel( name ) ) return false;
  labelIndex[labelPtr++] = name + "|";
  return true;
}

/*
 *  findLabel() - Returns true if label exists.
 *
 */

function findLabel( name ) {
  for( m=0; m<labelIndex.length; m++ ) {
    nameAndAddr = labelIndex[m].split( "|" );
    if( name == nameAndAddr[0] ) {
      return true;
    }
  }
  return false;
}

/*
 *  setLabelPC() - Associates label with address
 *
 */

function setLabelPC( name, addr ) {
  for( i=0; i<labelIndex.length; i++ ) {
    nameAndAddr = labelIndex[i].split( "|" );
    if( name == nameAndAddr[0] ) {
      labelIndex[i] = name + "|" + addr;
      return true;
    }
  }
  return false;
}

/*
 *  getLabelPC() - Get address associated with label
 *
 */

function getLabelPC( name ) {
  for( i=0; i<labelIndex.length; i++ ) {
    nameAndAddr = labelIndex[i].split( "|" );
    if( name == nameAndAddr[0] ) {
      return (nameAndAddr[1]);
    }
  }
  return -1;
}

/*
 *  compileLine()
 *
 *  Compiles one line of code.  Returns true if it compiled successfully,
 *  false otherwise.
 */

function compileLine( input, lineno ) {

  // remove comments

  input = input.replace( new RegExp( /^(.*?);.*/ ), "$1" );

  // trim line

  input = input.replace( new RegExp( /^\s+/ ), "" );
  input = input.replace( new RegExp( /\s+$/ ), "" );

  // Find command or label

  if( input.match( new RegExp( /^\w+:/ ) ) ) {
    label = input.replace( new RegExp( /(^\w+):.*$/ ), "$1" );
    if( input.match( new RegExp( /^\w+:[\s]*\w+.*$/ ) ) ) {
      input = input.replace( new RegExp( /^\w+:[\s]*(.*)$/ ), "$1" );
      command = input.replace( new RegExp( /^(\w+).*$/ ), "$1" );
    } else {
      command = "";
    }
  } else {
    command = input.replace( new RegExp( /^(\w+).*$/ ), "$1" );
  }

  // Blank line?  Return.

  if( command == "" )
    return true;

  command = command.toUpperCase();

  if( input.match( /^\*[\s]*=[\s]*[\$]?[0-9a-f]*$/ ) ) {
    // equ spotted
    param = input.replace( new RegExp( /^[\s]*\*[\s]*=[\s]*/ ), "" );
    if( param[0] == "$" ) {
      param = param.replace( new RegExp( /^\$/ ), "" );
      addr = parseInt( param, 16 );
    } else {
      addr = parseInt( param, 10 );
    }
    if( (addr < 0) || (addr > 0xffff) ) {
      message( "Unable to relocate code outside 64k memory" );
      return false;
    }
    defaultCodePC = addr;
    return true;
  }

  if( input.match( /^\w+\s+.*?$/ ) ) {
    param = input.replace( new RegExp( /^\w+\s+(.*?)/ ), "$1" );
  } else {
    if( input.match( /^\w+$/ ) ) {
      param = "";
    } else {
      return false;
    }
  }

  param = param.replace( /[ ]/g, "" );

  if( command == "DCB" )
    return DCB( param );

  for( o=0; o<Opcodes.length; o++ ) {
    if( Opcodes[o][0] == command ) {
      if( checkSingle( param, Opcodes[o][10] ) ) return true;
      if( checkImmediate( param, Opcodes[o][1] ) ) return true;
      if( checkZeroPage( param, Opcodes[o][2] ) ) return true;
      if( checkZeroPageX( param, Opcodes[o][3] ) ) return true;
      if( checkZeroPageY( param, Opcodes[o][4] ) ) return true;
      if( checkAbsoluteX( param, Opcodes[o][6] ) ) return true;
      if( checkAbsoluteY( param, Opcodes[o][7] ) ) return true;
      if( checkIndirectX( param, Opcodes[o][8] ) ) return true;
      if( checkIndirectY( param, Opcodes[o][9] ) ) return true;
      if( checkAbsolute( param, Opcodes[o][5] ) ) return true;
      if( checkBranch( param, Opcodes[o][11] ) ) return true;
    }
  }
  return false; // Unknown opcode
}

/*****************************************************************************
 ****************************************************************************/

function DCB( param ) {
  values = param.split( "," );
  if( values.length == 0 ) return false;
  for( v=0; v<values.length; v++ ) {
    str = values[v];
    if( str != undefined && str != null && str.length > 0 ) {
      ch = str.substring( 0, 1 );
      if( ch == "$" ) {
        number = parseInt( str.replace( /^\$/, "" ), 16 );
        pushByte( number );
      } else if( ch >= "0" && ch <= "9" ) {
        number = parseInt( str, 10 );
        pushByte( number );
      } else {
        return false;
      }
    }
  }
  return true;
}

/*
 *  checkBranch() - Commom branch function for all branches (BCC, BCS, BEQ, BNE..)
 *
 */

function checkBranch( param, opcode ) {
  if( opcode == 0x00 ) return false;

  addr = -1;
  if( param.match( /\w+/ ) )
    addr = getLabelPC( param );
  if( addr == -1 ) { pushWord( 0x00 ); return false; }
  pushByte( opcode );
  if( addr < (defaultCodePC-0x600) ) {  // Backwards?
    pushByte( (0xff - ((defaultCodePC-0x600)-addr)) & 0xff );
    return true;
  }
  pushByte( (addr-(defaultCodePC-0x600)-1) & 0xff );
  return true;
}

/*
 * checkImmediate() - Check if param is immediate and push value
 * 
 */

function checkImmediate( param, opcode ) {
  if( opcode == 0x00 ) return false;
  if( param.match( new RegExp( /^#\$[0-9a-f]{1,2}$/i ) ) ) {
    pushByte( opcode );
    value = parseInt( param.replace( /^#\$/, "" ), 16 );
    if( value < 0 || value > 255 ) return false;
    pushByte( value );
    return true;
  }
  if( param.match( new RegExp( /^#[0-9]{1,3}$/i ) ) ) {
    pushByte( opcode );
    value = parseInt( param.replace( /^#/, "" ), 10 );
    if( value < 0 || value > 255 ) return false;
    pushByte( value );
    return true;
  }
  // Label lo/hi
  if( param.match( new RegExp( /^#[<>]\w+$/ ) ) ) {
    label = param.replace( new RegExp( /^#[<>](\w+)$/ ), "$1" );
    hilo = param.replace( new RegExp( /^#([<>]).*$/ ), "$1" );
    pushByte( opcode );
    if( findLabel( label ) ) {
      addr = getLabelPC( label );
      switch( hilo ) {
        case ">":
          pushByte( (addr >> 8) & 0xff );
          return true;
          break;
        case "<":
          pushByte( addr & 0xff );
          return true;
          break;
        default:
          return false;
          break;
      }
    } else {
      pushByte( 0x00 );
      return true;
    }
  }
  return false;
}

/*
 * checkIndirectX() - Check if param is indirect X and push value
 * 
 */

function checkIndirectX( param, opcode ) {
  if( opcode == 0x00 ) return false;
  if( param.match( /^\(\$[0-9a-f]{1,2},X\)$/i ) ) {
    pushByte( opcode );
    value = param.replace( new RegExp( /^\(\$([0-9a-f]{1,2}).*$/i ), "$1" );
    if( value < 0 || value > 255 ) return false;
    pushByte( parseInt( value, 16 ) );
    return true;
  }
  return false;
}

/*
 * checkIndirectY() - Check if param is indirect Y and push value
 * 
 */

function checkIndirectY( param, opcode ) {
  if( opcode == 0x00 ) return false;
  if( param.match( /^\(\$[0-9a-f]{1,2}\),Y$/i ) ) {
    pushByte( opcode );
    value = param.replace( new RegExp( /^\([\$]([0-9a-f]{1,2}).*$/i ), "$1" );
    if( value < 0 || value > 255 ) return false;
    pushByte( parseInt( value, 16 ) );
    return true;
  }
  return false;
}

/*
 *  checkSingle() - Single-byte opcodes
 *
 */

function checkSingle( param, opcode ) {
  if( opcode == 0x00 ) return false;
  if( param != "" ) return false;
  pushByte( opcode );
  return true;
}

/*
 *  checkZeroaPage() - Check if param is ZP and push value
 *
 */

function checkZeroPage( param, opcode ) {
  if( opcode == 0x00 ) return false;
  if( param.match( /^\$[0-9a-f]{1,2}$/i ) ) {
    pushByte( opcode );
    value = parseInt( param.replace( /^\$/, "" ), 16 );
    if( value < 0 || value > 255 ) return false;
    pushByte( value );
    return true;
  }
  if( param.match( /^[0-9]{1,3}$/i ) ) {
    pushByte( opcode );
    value = parseInt( param, 10 );
    if( value < 0 || value > 255 ) return false;
    pushByte( value );
    return true;
  }
  return false;
}

/*
 *  checkAbsoluteX() - Check if param is ABSX and push value
 *
 */

function checkAbsoluteX( param, opcode ) {
  if( opcode == 0x00 ) return false;
  if( param.match( /^\$[0-9a-f]{3,4},X$/i ) ) {
    pushByte( opcode );
    number = param.replace( new RegExp( /^\$([0-9a-f]*),X/i ), "$1" );
    value = parseInt( number, 16 );
    if( value < 0 || value > 0xffff ) return false;
    pushWord( value );
    return true;
  }

  if( param.match( /^\w+,X$/i ) ) {
    param = param.replace( new RegExp( /,X$/i ), "" );
    pushByte( opcode );
    if( findLabel( param ) ) {
      addr = getLabelPC( param );
      if( addr < 0 || addr > 0xffff ) return false;
      pushWord( addr );
      return true;
    } else {
      pushWord( 0x1234 );
      return true;
    }
  }

  return false;
}

/*
 *  checkAbsoluteY() - Check if param is ABSY and push value
 *
 */

function checkAbsoluteY( param, opcode ) {
  if( opcode == 0x00 ) return false;
  if( param.match( /^\$[0-9a-f]{3,4},Y$/i ) ) {
    pushByte( opcode );
    number = param.replace( new RegExp( /^\$([0-9a-f]*),Y/i ), "$1" );
    value = parseInt( number, 16 );
    if( value < 0 || value > 0xffff ) return false;
    pushWord( value );
    return true;
  }

  // it could be a label too..

  if( param.match( /^\w+,Y$/i ) ) {
    param = param.replace( new RegExp( /,Y$/i ), "" );
    pushByte( opcode );
    if( findLabel( param ) ) {
      addr = getLabelPC( param );
      if( addr < 0 || addr > 0xffff ) return false;
      pushWord( addr );
      return true;
    } else {
      pushWord( 0x1234 );
      return true;
    }
  }
  return false;
}

/*
 *  checkZeroPageX() - Check if param is ZPX and push value
 *
 */

function checkZeroPageX( param, opcode ) {
  if( opcode == 0x00 ) return false;
  if( param.match( /^\$[0-9a-f]{1,2},X/i ) ) {
    pushByte( opcode );
    number = param.replace( new RegExp( /^\$([0-9a-f]{1,2}),X/i ), "$1" );
    value = parseInt( number, 16 );
    if( value < 0 || value > 255 ) return false;
    pushByte( value );
    return true;
  }
  if( param.match( /^[0-9]{1,3},X/i ) ) {
    pushByte( opcode );
    number = param.replace( new RegExp( /^([0-9]{1,3}),X/i ), "$1" );
    value = parseInt( number, 10 );
    if( value < 0 || value > 255 ) return false;
    pushByte( value );
    return true;
  }
  return false;
}

function checkZeroPageY( param, opcode ) {
  if( opcode == 0x00 ) return false;
  if( param.match( /^\$[0-9a-f]{1,2},Y/i ) ) {
    pushByte( opcode );
    number = param.replace( new RegExp( /^\$([0-9a-f]{1,2}),Y/i ), "$1" );
    value = parseInt( number, 16 );
    if( value < 0 || value > 255 ) return false;
    pushByte( value );
    return true;
  }
  if( param.match( /^[0-9]{1,3},Y/i ) ) {
    pushByte( opcode );
    number = param.replace( new RegExp( /^([0-9]{1,3}),Y/i ), "$1" );
    value = parseInt( number, 10 );
    if( value < 0 || value > 255 ) return false;
    pushByte( value );
    return true;
  }
  return false;
}

/*
 *  checkAbsolute() - Check if param is ABS and push value
 *
 */

function checkAbsolute( param, opcode ) {
  if( opcode == 0x00 ) return false;
  pushByte( opcode );
  if( param.match( /^\$[0-9a-f]{3,4}$/i ) ) {
    value = parseInt( param.replace( /^\$/, "" ), 16 );
    if( value < 0 || value > 0xffff ) return false;
    pushWord( value );
    return true;
  }
  // it could be a label too..
  if( param.match( /^\w+$/ ) ) {
    if( findLabel( param ) ) {
      addr = (getLabelPC( param ));
      if( addr < 0 || addr > 0xffff ) return false;
      pushWord( addr );
      return true;
    } else {
      pushWord( 0x1234 );
      return true;
    }
  }
  return false;
}

/*****************************************************************************
 ****************************************************************************/

/*
 *  stackPush() - Push byte to stack
 *
 */

function stackPush( value ) {
  if( regSP >= 0 ) {
    regSP--;
    memory[(regSP&0xff)+0x100] = value & 0xff;
  } else {
    message( "Stack full: " + regSP );
    codeRunning = false;
  }
}

/*****************************************************************************
 ****************************************************************************/

/*
 *  stackPop() - Pop byte from stack
 *
 */

function stackPop() {
  if( regSP < 0x100 ) {
    value = memory[regSP+0x100];
    regSP++;
    return value;
  } else {
    message( "Stack empty" );
    codeRunning = false;
    return 0;
  }
}

/*
 * pushByte() - Push byte to compiledCode variable
 *
 */

function pushByte( value ) {
  memory[defaultCodePC] = value & 0xff;
  defaultCodePC++;
  codeLen++;
}

/*
 * pushWord() - Push a word using pushByte twice
 *
 */

function pushWord( value ) {
  pushByte( value & 0xff );
  pushByte( (value>>8) & 0xff );
}

/*
 * popByte() - Pops a byte
 *
 */

function popByte() {
  return( memory[regPC++] & 0xff );
}

/*
 * popWord() - Pops a word using popByte() twice
 *
 */

function popWord() {
  return popByte() + (popByte() << 8);
}

/*
 * memStoreByte() - Poke a byte, don't touch any registers
 *
 */

function memStoreByte( addr, value ) {
  memory[ addr ] = (value & 0xff);
  if( (addr >= 0x200) && (addr<=0x5ff) ) 
    display[addr-0x200].background = palette[memory[addr] & 0x0f];
}

/*
 * memStoreByte() - Peek a byte, don't touch any registers
 *
 */

function memReadByte( addr ) {
  if( addr == 0xfe ) return Math.floor( Math.random()*256 );
  return memory[addr];
}

/*
 *  hexDump() - Dump binary as hex to new window
 *
 */

function addr2hex( addr ) {
  return num2hex((addr>>8)&0xff)+num2hex(addr&0xff);
}

function num2hex( nr ) {
  str = "0123456789abcdef";
  hi = ((nr&0xf0)>>4);
  lo = (nr&15);
  return str.substring( hi, hi+1  ) + str.substring( lo, lo+1 );
}

function hexDump() {
  w = window.open('', 'hexdump', 'width=500,height=300,resizable=yes,scrollbars=yes,toolbar=no,location=no,menubar=no,status=no' );

  html = "<html><head>";
  html += "<link href='style.css' rel='stylesheet' type='text/css' />";
  html += "<title>hexdump</title></head><body>";
  html += "<code>";
  for( x=0; x<codeLen; x++ ) {
    if( (x&15) == 0 ) {
      html += "<br/> ";
      n = (0x600+x);
      html += num2hex( ((n>>8)&0xff) );
      html += num2hex( (n&0xff) );
      html += ": ";
    }
    html += num2hex( memory[0x600+x] );
    if( x&1 ) html += " ";
  }
  if( (x&1) ) html += "-- [END]";
  html += "</code></body></html>";
  w.document.write( html );
  w.document.close();
}

/*
 *  runBinary() - Executes the compiled code
 *
 */

function runBinary() {
  if( codeRunning ) {
    codeRunning = false;
    document.getElementById( "runButton" ).value = "Run";
    document.getElementById( "hexdumpButton" ).disabled = false;
    document.getElementById( "fileSelect" ).disabled = false;
    clearInterval( myInterval );
  } else {
    reset();
    document.getElementById( "runButton" ).value = "Stop";
    document.getElementById( "fileSelect" ).disabled = true;
    document.getElementById( "hexdumpButton" ).disabled = true;
    codeRunning = true;
    myInterval = setInterval( "multiexecute()", 1 );
    //execute();
  }
}

/*
 *  readZeroPage() - Get value from ZP
 *
 */

function jumpBranch( offset ) {
  if( offset > 0x7f )
    regPC = (regPC - (0x100 - offset));
  else
    regPC = (regPC + offset );
}

function doCompare( reg, val ) {
  if( (reg+val) > 0xff ) regP |= 1; else regP &= 0xfe;
  val = (reg-val);
//  if( reg+0x100-val > 0xff ) regP |= 1; else regP &= 0xfe;
//  val = reg+0x100-val;
  if( val ) regP &= 0xfd; else regP |= 0x02;
  if( val & 0x80 ) regP |= 0x80; else regP &= 0x7f;
}

function testSBC( value ) {
  if( (regA ^ value ) & 0x80 )
    vflag = 1;
  else
    vflag = 0;

  if( regP & 8 ) {
    tmp = 0xf + (regA & 0xf) - (value & 0xf) + (regP&1);
    if( tmp < 0x10 ) {
      w = 0;
      tmp -= 6;
    } else {
      w = 0x10;
      tmp -= 0x10;
    }
    w += 0xf0 + (regA & 0xf0) - (value & 0xf0);
    if( w < 0x100 ) {
      regP &= 0xfe;
      if( (regP&0xbf) && w<0x80) regP&=0xbf;
      w -= 0x60;
    } else {
      regP |= 1;
      if( (regP&0xbf) && w>=0x180) regP&=0xbf;
    }
    w += tmp;
  } else {
    w = 0xff + regA - value + (regP&1);
    if( w<0x100 ) {
      regP &= 0xfe;
      if( (regP&0xbf) && w<0x80 ) regP&=0xbf;
    } else {
      regP |= 1;
      if( (regP&0xbf) && w>= 0x180) regP&=0xbf;
    }
  }
  regA = w & 0xff;
  if( regA ) regP &= 0xfd; else regP |= 0x02;
  if( regA & 0x80 ) regP |= 0x80; else regP &= 0x7f;
}

function testADC( value ) {
  if( (regA ^ value) & 0x80 ) {
    regP &= 0xbf;
  } else {
    regP |= 0x40;
  }

  if( regP & 8 ) {
    tmp = (regA & 0xf) + (value & 0xf) + (regP&1);
    if( tmp >= 10 ) {
      tmp = 0x10 | ((tmp+6)&0xf);
    }
    tmp += (regA & 0xf0) + (value & 0xf0);
    if( tmp >= 160) {
      regP |= 1;
      if( (regP&0xbf) && tmp >= 0x180 ) regP &= 0xbf;
      tmp += 0x60;
    } else {
      regP &= 0xfe;
      if( (regP&0xbf) && tmp<0x80 ) regP &= 0xbf;
    }
  } else {
    tmp = regA + value + (regP&1);
    if( tmp >= 0x100 ) {
      regP |= 1;
      if( (regP&0xbf) && tmp>=0x180) regP &= 0xbf;
    } else {
      regP &= 0xfe;
      if( (regP&0xbf) && tmp<0x80) regP &= 0xbf;
    }
  }
  regA = tmp & 0xff;
  if( regA ) regP &= 0xfd; else regP |= 0x02;
  if( regA & 0x80 ) regP |= 0x80; else regP &= 0x7f;
}

function multiexecute() {
  for( w=0; w<128; w++ ) execute();
}

/*
 *  execute() - Executes one instruction.
 *              This is the main part of the CPU emulator.
 *
 */

function execute() {
  if( ! codeRunning ) return;

  opcode = popByte();
//  message( "PC=" + addr2hex(regPC-1) + " opcode=" + opcode + " X="+regX + " Y=" + regY + " A=" + regA );
  switch( opcode ) {
    case 0x00:                            // BRK implied
      codeRunning = false;
      break;
    case 0x01:                            // ORA INDX
      addr = popByte() + regX;
      value = memReadByte( addr ) + (memReadByte( addr+1) << 8);
      regA |= value;
      if( regA ) regP &= 0xfd; else regP |= 0x02;
      if( regA & 0x80 ) regP |= 0x80; else regP &= 0x7f;
      break;
    case 0x05:                            // ORA ZP
      zp = popByte();
      regA |= memReadByte( zp );
      if( regA ) regP &= 0xfd; else regP |= 0x02;
      if( regA & 0x80 ) regP |= 0x80; else regP &= 0x7f;
      break;
    case 0x06:                            // ASL ZP
      zp = popByte();
      value = memReadByte( zp );
      regP = (regP & 0xfe) | ((value>>7)&1);
      value = value << 1;
      memStoreByte( zp, value );
      if( value ) regP &= 0xfd; else regP |= 0x02;
      if( value & 0x80 ) regP |= 0x80; else regP &= 0x7f;
      break;
    case 0x08:                            // PHP
      stackPush( regP );
      break;
    case 0x09:                            // ORA IMM
      regA |= popByte();
      if( regA ) regP &= 0xfd; else regP |= 0x02;
      if( regA & 0x80 ) regP |= 0x80; else regP &= 0x7f;
      break;
    case 0x0a:                            // ASL IMPL
      regP = (regP & 0xfe) | ((regA>>7)&1);
      regA = regA<<1;
      if( regA ) regP &= 0xfd; else regP |= 0x02;
      if( regA & 0x80 ) regP |= 0x80; else regP &= 0x7f;
      break;
    case 0x0d:                            // ORA ABS
      regA |= memReadByte( popWord() );
      break;
    case 0x0e:                            // ASL ABS
      addr = popWord();
      value = memReadByte( addr );
      regP = (regP & 0xfe) | ((value>>7)&1);
      value = value << 1;
      memStoreByte( addr, value );
      break;
    case 0x10:                            // BPL
      offset = popByte();
      if( (regP & 0x80) == 0 ) jumpBranch( offset );
      break;
    case 0x11:                            // ORA INDY
      zp = popByte();
      value = memReadByte(zp) + (memReadByte(zp+1)<<8) + regY;
      regA |= memReadByte(value);
      if( regA ) regP &= 0xfd; else regP |= 0x02;
      if( regA & 0x80 ) regP |= 0x80; else regP &= 0x7f;
      break;
    case 0x15:                            // ORA ZPX
      addr = (popByte() + regX) & 0xff;
      regA |= memReadByte(addr);
      if( regA ) regP &= 0xfd; else regP |= 0x02;
      if( regA & 0x80 ) regP |= 0x80; else regP &= 0x7f;
      break;
    case 0x16:                            // ASL ZPX
      addr = (popByte() + regX) & 0xff;
      value = memReadByte(addr);
      regP = (regP & 0xfe) | ((value>>7)&1);
      value = value << 1;
      memStoreByte( addr, value );
      if( value ) regP &= 0xfd; else regP |= 0x02;
      if( value & 0x80 ) regP |= 0x80; else regP &= 0x7f;
      break;
    case 0x18:                            // CLC
      regP &= 0xfe;
      break;
    case 0x19:                            // ORA ABSY
      addr = popWord() + regY;
      regA |= memReadByte( addr );
      if( regA ) regP &= 0xfd; else regP |= 0x02;
      if( regA & 0x80 ) regP |= 0x80; else regP &= 0x7f;
      break;
    case 0x1d:                            // ORA ABSX
      addr = popWord() + regX;
      regA |= memReadByte( addr );
      if( regA ) regP &= 0xfd; else regP |= 0x02;
      if( regA & 0x80 ) regP |= 0x80; else regP &= 0x7f;
      break;
    case 0x1e:                            // ASL ABSX
      addr = popWord() + regX;
      value = memReadByte( addr );
      regP = (regP & 0xfe) | ((value>>7)&1);
      value = value << 1;
      memStoreByte( addr, value );
      if( value ) regP &= 0xfd; else regP |= 0x02;
      if( value & 0x80 ) regP |= 0x80; else regP &= 0x7f;
      break;
    case 0x20:                            // JSR ABS
      addr = popWord();
      currAddr = regPC-1;
      stackPush( ((currAddr >> 8) & 0xff) );
      stackPush( (currAddr & 0xff) );
      regPC = addr;
      break;
    case 0x21:                            // AND INDX
      addr = (popByte() + regX)&0xff;
      value = memReadByte( addr ) + (memReadByte( addr+1) << 8);
      regA &= value;
      if( regA ) regP &= 0xfd; else regP |= 0x02;
      if( regA & 0x80 ) regP |= 0x80; else regP &= 0x7f;
      break;
    case 0x24:                            // BIT ZP
      zp = popByte();
      value = memReadByte( zp );
      if( value & regA ) regP &= 0xfd; else regP |= 0x02;
      regP = (regP & 0x3f) | (value & 0xc0);
      break;
    case 0x25:                            // AND ZP
      zp = popByte();
      value = memReadByte( zp ) & regA;
      memStoreByte( zp, value );
      break;
    case 0x26:                            // ROL ZP
      sf = (regP & 1);
      addr = popByte();
      value = memReadByte( addr ) & regA;
      regP = (regP & 0xfe) | ((value>>7)&1);
      value = value << 1;
      value |= sf;
      memStoreByte( addr, value );
      if( value ) regP &= 0xfd; else regP |= 0x02;
      if( value & 0x80 ) regP |= 0x80; else regP &= 0x7f;
      break;
    case 0x28:                            // PLP
      regP = stackPop() | 0x20;
      break;
    case 0x29:                            // AND IMM
      regA &= popByte();
      if( regA ) regP &= 0xfd; else regP |= 0x02;
      if( regA & 0x80 ) regP |= 0x80; else regP &= 0x7f;
      break;
    case 0x2a:                            // ROL A
      sf = (regP&1);
      regP = (regP&0xfe) | ((regA>>7)&1);
      regA = regA << 1;
      regA |= sf;
      if( regA ) regP &= 0xfd; else regP |= 0x02;
      if( regA & 0x80 ) regP |= 0x80; else regP &= 0x7f;
      break;
    case 0x2c:                            // BIT ABS
      value = memReadByte( popWord() );
      if( value & regA ) regP &= 0xfd; else regP |= 0x02;
      regP = (regP & 0x3f) | (value & 0xc0);
      break;
    case 0x2d:                            // AND ABS
      value = memReadByte( popWord() );
      regA &= value;
      if( regA ) regP &= 0xfd; else regP |= 0x02;
      if( regA & 0x80 ) regP |= 0x80; else regP &= 0x7f;
      break;
    case 0x2e:                            // ROL ABS
      sf = regP & 1;
      addr = popWord();
      value = memReadByte( addr );
      regP = (regP & 0xfe) | ((value>>7)&1);
      value = value << 1;
      value |= sf;
      memStoreByte( addr, value );
      if( value ) regP &= 0xfd; else regP |= 0x02;
      if( value & 0x80 ) regP |= 0x80; else regP &= 0x7f;
      break;
    case 0x30:                            // BMI
      offset = popByte();
      if( regP & 0x80 ) jumpBranch( offset );
      break;
    case 0x31:                            // AND INDY
      zp = popByte();
      value = memReadByte(zp) + (memReadByte(zp+1)<<8) + regY;
      regA &= memReadByte(value);
      if( regA ) regP &= 0xfd; else regP |= 0x02;
      if( regA & 0x80 ) regP |= 0x80; else regP &= 0x7f;
      break;
    case 0x35:                            // AND INDX
      zp = popByte();
      value = memReadByte(zp) + (memReadByte(zp+1)<<8) + regX;
      regA &= memReadByte(value);
      if( regA ) regP &= 0xfd; else regP |= 0x02;
      if( regA & 0x80 ) regP |= 0x80; else regP &= 0x7f;
      break;
    case 0x36:                            // ROL ZPX
      sf = regP & 1;
      addr = (popByte() + regX) & 0xff;
      value = memReadByte( addr );
      regP = (regP & 0xfe) | ((value>>7)&1);
      value = value << 1;
      value |= sf;
      memStoreByte( addr, value );
      if( value ) regP &= 0xfd; else regP |= 0x02;
      if( value & 0x80 ) regP |= 0x80; else regP &= 0x7f;
      break;
    case 0x38:                            // SEC
      regP |= 1;
      break;
    case 0x39:                            // AND ABSY
      addr = popWord() + regY;
      value = memReadByte( addr );
      regA &= value;
      if( regA ) regP &= 0xfd; else regP |= 0x02;
      if( regA & 0x80 ) regP |= 0x80; else regP &= 0x7f;
      break;
    case 0x3d:                            // AND ABSX
      addr = popWord() + regX;
      value = memReadByte( addr );
      regA &= value;
      if( regA ) regP &= 0xfd; else regP |= 0x02;
      if( regA & 0x80 ) regP |= 0x80; else regP &= 0x7f;
      break;
    case 0x3e:                            // ROL ABSX
      sf = regP&1;
      addr = popWord() + regX;
      value = memReadByte( addr );
      regP = (regP & 0xfe) | ((value>>7)&1);
      value = value << 1;
      value |= sf;
      memStoreByte( addr, value );
      if( value ) regP &= 0xfd; else regP |= 0x02;
      if( value & 0x80 ) regP |= 0x80; else regP &= 0x7f;
      break;
    case 0x40:                            // RTI (unsupported, =NOP)
      break;
    case 0x41:                            // EOR INDX
      zp = (popByte() + regX)&0xff;
      value = memReadByte(zp) + (memReadByte(zp+1)<<8);
      regA ^= memReadByte(value);
      if( regA ) regP &= 0xfd; else regP |= 0x02;
      if( regA & 0x80 ) regP |= 0x80; else regP &= 0x7f;
      break;
    case 0x45:                            // EOR ZPX
      addr = (popByte() + regX) & 0xff;
      value = memReadByte( addr );
      regA ^= value;
      if( regA ) regP &= 0xfd; else regP |= 0x02;
      if( regA & 0x80 ) regP |= 0x80; else regP &= 0x7f;
      break;
    case 0x46:                            // LSR ZP
      addr = popByte() & 0xff;
      value = memReadByte( addr );
      regP = (regP & 0xfe) | (value&1);
      value = value >> 1;
      memStoreByte( addr, value );
      if( value != 0 ) regP &= 0xfd; else regP |= 2;
      if( (value&0x80) == 0x80 ) regP |= 0x80; else regP &= 0x7f;
      break;
    case 0x48:                            // PHA
      stackPush( regA );
      break;
    case 0x49:                            // EOR IMM
      regA ^= popByte();
      if( regA ) regP &= 0xfd; else regP |= 0x02;
      if( regA & 0x80 ) regP |= 0x80; else regP &= 0x7f;
      break;
    case 0x4a:                            // LSR
      regP = (regP&0xfe) | (regA&1);
      regA = regA >> 1;
      if( regA ) regP &= 0xfd; else regP |= 0x02;
      if( regA & 0x80 ) regP |= 0x80; else regP &= 0x7f;
      break;
    case 0x4c:                            // JMP abs
      regPC = popWord();
      break;
    case 0x4d:                            // EOR abs
      addr = popWord();
      value = memReadByte( addr );
      regA ^= value;
      if( regA ) regP &= 0xfd; else regP |= 0x02;
      if( regA & 0x80 ) regP |= 0x80; else regP &= 0x7f;
      break;
    case 0x4e:                           // LSR abs
      addr = popWord();
      value = memReadByte( addr );
      regP = (regP&0xfe)|(value&1);
      value = value >> 1;
      memStoreByte( addr, value );
      if( value ) regP &= 0xfd; else regP |= 0x02;
      if( value & 0x80 ) regP |= 0x80; else regP &= 0x7f;
      break;
    case 0x50:                           // BVC (on overflow clear)
      offset = popByte();
      if( (regP & 0x40) == 0 ) jumpBranch( offset );
      break;
    case 0x51:                           // EOR INDY
      zp = popByte();
      value = memReadByte(zp) + (memReadByte(zp+1)<<8) + regY;
      regA ^= memReadByte(value);
      if( regA ) regP &= 0xfd; else regP |= 0x02;
      if( regA & 0x80 ) regP |= 0x80; else regP &= 0x7f;
      break;
    case 0x55:                           // EOR ZPX
      addr = (popByte() + regX) & 0xff;
      regA ^= memReadByte( addr );
      if( regA ) regP &= 0xfd; else regP |= 0x02;
      if( regA & 0x80 ) regP |= 0x80; else regP &= 0x7f;
      break;
    case 0x56:                           // LSR ZPX
      addr = (popByte() + regX) & 0xff;
      value = memReadByte( addr );
      regP = (regP&0xfe) | (value&1);
      value = value >> 1;
      memStoreByte( addr, value );
      if( value ) regP &= 0xfd; else regP |= 0x02;
      if( value & 0x80 ) regP |= 0x80; else regP &= 0x7f;
      break;
    case 0x58:                           // CLI (does nothing)
      break;
    case 0x59:                           // EOR ABSY
      addr = popWord() + regY;
      value = memReadByte( addr );
      regA ^= value;
      if( regA ) regP &= 0xfd; else regP |= 0x02;
      if( regA & 0x80 ) regP |= 0x80; else regP &= 0x7f;
      break;
    case 0x5d:                           // EOR ABSX
      addr = popWord() + regX;
      value = memReadByte( addr );
      regA ^= value;
      if( regA ) regP &= 0xfd; else regP |= 0x02;
      if( regA & 0x80 ) regP |= 0x80; else regP &= 0x7f;
      break;
    case 0x5e:                           // LSR ABSX
      addr = popWord() + regX;
      value = memReadByte( addr );
      regP = (regP&0xfe) | (value&1);
      value = value >> 1;
      memStoreByte( addr, value );
      if( value ) regP &= 0xfd; else regP |= 0x02;
      if( value & 0x80 ) regP |= 0x80; else regP &= 0x7f;
      break;
    case 0x60:                           // RTS
      regPC = (stackPop()+1) | (stackPop()<<8);
      break;
    case 0x61:                           // ADC INDX
      zp = (popByte() + regX)&0xff;
      addr = memReadByte(zp) + (memReadByte(zp+1)<<8);
      value = memReadByte( addr );
      testADC( value );
      break;
    case 0x65:                           // ADC ZP
      addr = popByte();
      value = memReadByte( addr );
      testADC( value );
      break;
    case 0x66:                           // ROR ZP
      sf = regP&1;
      addr = popByte();
      value = memReadByte( addr );
      regP = (regP&0xfe)|(value&1);
      value = value >> 1;
      if( sf ) value |= 0x80;
      memStoreByte( addr, value );
      if( value ) regP &= 0xfd; else regP |= 0x02;
      if( value & 0x80 ) regP |= 0x80; else regP &= 0x7f;
      break;
    case 0x68:                           // PLA
      regA = stackPop();
      if( regA ) regP &= 0xfd; else regP |= 0x02;
      if( regA & 0x80 ) regP |= 0x80; else regP &= 0x7f;
      break;
    case 0x69:                           // ADC IMM
      value = popByte();
      testADC( value );
      break;
    case 0x6a:                           // ROR A
      sf = regP&1;
      regP = (regP&0xfe) | (regA&1);
      regA = regA >> 1;
      if( sf ) regA |= 0x80;
      if( regA ) regP &= 0xfd; else regP |= 0x02;
      if( regA & 0x80 ) regP |= 0x80; else regP &= 0x7f;
      break;
    case 0x6c: // JMP INDIR
//      regPC = memReadByte(popByte()) + (memReadByte(popByte())<<8);
      break;
    case 0x6d:                           // ADC ABS
      addr = popWord();
      value = memReadByte( addr );
      testADC( value );
      break;
    case 0x6e:                           // ROR ABS
      sf = regP&1;
      addr = popWord();
      value = memReadByte( addr );
      regP = (regP&0xfe)|(value&1);
      value = value >> 1;
      if( sf ) value |= 0x80;
      memStoreByte( addr, value );
      if( value ) regP &= 0xfd; else regP |= 0x02;
      if( value & 0x80 ) regP |= 0x80; else regP &= 0x7f;
      break;
    case 0x70:                           // BVS (branch on overflow set)
      offset = popByte();
      if( regP & 0x40 ) jumpBranch( offset );
      break;
    case 0x71:                           // ADC INY
      zp = popByte();
      addr = memReadByte(zp) + (memReadByte(zp+1)<<8);
      value = memReadByte( addr + regY );
      testADC( value );
      break;
    case 0x75:                           // ADC ZPX
      addr = (popByte() + regX) & 0xff;
      value = memReadByte( addr );
      regP = (regP&0xfe) | (value&1);
      testADC( value );
      break;
    case 0x76:                           // ROR ZPX
      sf = (regP&1);
      addr = (popByte() + regX) & 0xff;
      value = memReadByte( addr );
      regP = (regP&0xfe) | (value&1);
      value = value >> 1;
      if( sf ) value |= 0x80;
      memStoreByte( addr, value );
      if( value ) regP &= 0xfd; else regP |= 0x02;
      if( value & 0x80 ) regP |= 0x80; else regP &= 0x7f;
      break;
    case 0x78:                           // SEI (does nothing)
      break;
    case 0x79:                           // ADC ABSY
      addr = popWord();
      value = memReadByte( addr + regY );
      testADC( value );
      break;
    case 0x7d:                           // ADC ABSX
      addr = popWord();
      value = memReadByte( addr + regX );
      testADC( value );
      break;
    case 0x7e:                           // ROR ABSX
      sf = regP&1;
      addr = popWord() + regX;
      value = memReadByte( addr );
      regP = (regP&0xfe) | (value&1);
      value = value >> 1;
      if( value ) value |= 0x80;
      memStoreByte( addr, value );
      if( value ) regP &= 0xfd; else regP |= 0x02;
      if( value & 0x80 ) regP |= 0x80; else regP &= 0x7f;
      break;
    case 0x81:                           // STA INDX
      zp = (popByte()+regX)&0xff;
      addr = memReadByte(zp) + (memReadByte(zp+1)<<8);
      memStoreByte( addr, regA );
      break;
    case 0x84:                           // STY ZP
      memStoreByte( popByte(), regY );
      break;
    case 0x85:                           // STA ZP
      memStoreByte( popByte(), regA );
      break;
    case 0x86:                           // STX ZP
      memStoreByte( popByte(), regX );
      break;
    case 0x88:                           // DEY (1 byte)
      regY = (regY-1) & 0xff;
      if( regY ) regP &= 0xfd; else regP |= 0x02;
      if( regY & 0x80 ) regP |= 0x80; else regP &= 0x7f;
      break;
    case 0x8a:                           // TXA (1 byte);
      regA = regX & 0xff;
      if( regA ) regP &= 0xfd; else regP |= 0x02;
      if( regA & 0x80 ) regP |= 0x80; else regP &= 0x7f;
      break;
    case 0x8c:                           // STY abs
      memStoreByte( popWord(), regY );
      break;
    case 0x8d:                           // STA ABS (3 bytes)
      memStoreByte( popWord(), regA );
      break;
    case 0x8e:                           // STX abs
      memStoreByte( popWord(), regX );
      break;
    case 0x90:                           // BCC (branch on carry clear)
      offset = popByte();
      if( ( regP & 1 ) == 0 ) jumpBranch( offset );
      break;
    case 0x91:                           // STA INDY
      zp = popByte();
      addr = memReadByte(zp) + (memReadByte(zp+1)<<8) + regY;
      memStoreByte( addr, regA );
      break;
    case 0x94:                           // STY ZPX
      memStoreByte( popByte() + regX, regY );
      break;
    case 0x95:                           // STA ZPX
      memStoreByte( popByte() + regX, regA );
      break;
    case 0x96:                           // STX ZPY
      memStoreByte( popByte() + regY, regX );
      break;
    case 0x98:                           // TYA
      regA = regY & 0xff;
      if( regA ) regP &= 0xfd; else regP |= 0x02;
      if( regA & 0x80 ) regP |= 0x80; else regP &= 0x7f;
      break;
    case 0x99:                           // STA ABSY
      memStoreByte( popWord() + regY, regA );
      break;
    case 0x9a:                           // TXS
      regSP = regX & 0xff;
      break;
    case 0x9d:                           // STA ABSX
      addr = popWord();
      memStoreByte( addr + regX, regA );
      break;
    case 0xa0:                           // LDY IMM
      regY = popByte();
      if( regY ) regP &= 0xfd; else regP |= 0x02;
      if( regY & 0x80 ) regP |= 0x80; else regP &= 0x7f;
      break;
    case 0xa1:                           // LDA INDX
      zp = (popByte()+regX)&0xff;
      addr = memReadByte(zp) + (memReadByte(zp+1)<<8);
      regA = memReadByte( addr );
      if( regA ) regP &= 0xfd; else regP |= 0x02;
      if( regA & 0x80 ) regP |= 0x80; else regP &= 0x7f;
      break;
    case 0xa2:                           // LDX IMM
      regX = popByte();
      if( regX ) regP &= 0xfd; else regP |= 0x02;
      if( regX & 0x80 ) regP |= 0x80; else regP &= 0x7f;
      break;
    case 0xa4:                           // LDY ZP
      regY = memReadByte( popByte() );
      if( regY ) regP &= 0xfd; else regP |= 0x02;
      if( regY & 0x80 ) regP |= 0x80; else regP &= 0x7f;
      break;
    case 0xa5:                           // LDA ZP
      regA = memReadByte( popByte() );
      if( regA ) regP &= 0xfd; else regP |= 0x02;
      if( regA & 0x80 ) regP |= 0x80; else regP &= 0x7f;
      break;
    case 0xa6:                          // LDX ZP
      regX = memReadByte( popByte() );
      if( regX ) regP &= 0xfd; else regP |= 0x02;
      if( regX & 0x80 ) regP |= 0x80; else regP &= 0x7f;
      break;
    case 0xa8:                          // TAY
      regY = regA & 0xff;
      if( regY ) regP &= 0xfd; else regP |= 0x02;
      if( regY & 0x80 ) regP |= 0x80; else regP &= 0x7f;
      break;
    case 0xa9:                          // LDA IMM
      regA = popByte();
      if( regA ) regP &= 0xfd; else regP |= 0x02;
      if( regA & 0x80 ) regP |= 0x80; else regP &= 0x7f;
      break;
    case 0xaa:                          // TAX
      regX = regA & 0xff;
      if( regX ) regP &= 0xfd; else regP |= 0x02;
      if( regX & 0x80 ) regP |= 0x80; else regP &= 0x7f;
      break;
    case 0xac:                          // LDY ABS
      regY = memReadByte( popWord() );
      if( regY ) regP &= 0xfd; else regP |= 0x02;
      if( regY & 0x80 ) regP |= 0x80; else regP &= 0x7f;
      break;
    case 0xad:                          // LDA ABS
      regA = memReadByte( popWord() );
      if( regA ) regP &= 0xfd; else regP |= 0x02;
      if( regA & 0x80 ) regP |= 0x80; else regP &= 0x7f;
      break;
    case 0xae:                          // LDX ABS
      regX = memReadByte( popWord() );
      if( regX ) regP &= 0xfd; else regP |= 0x02;
      if( regX & 0x80 ) regP |= 0x80; else regP &= 0x7f;
      break;
    case 0xb0:                          // BCS
      offset = popByte();
      if( regP & 1 ) jumpBranch( offset );
      break;
    case 0xb1:                          // LDA INDY
      zp = popByte();
      addr = memReadByte(zp) + (memReadByte(zp+1)<<8) + regY;
      regA = memReadByte( addr );
      if( regA ) regP &= 0xfd; else regP |= 0x02;
      if( regA & 0x80 ) regP |= 0x80; else regP &= 0x7f;
      break; 
    case 0xb4:                          // LDY ZPX
      regY = memReadByte( popByte() + regX );
      if( regY ) regP &= 0xfd; else regP |= 0x02;
      if( regY & 0x80 ) regP |= 0x80; else regP &= 0x7f;
      break;
    case 0xb5:                          // LDA ZPX
      regA = memReadByte( (popByte() + regX) & 0xff );
      if( regA ) regP &= 0xfd; else regP |= 0x02;
      if( regA & 0x80 ) regP |= 0x80; else regP &= 0x7f;
      break;
    case 0xb6:                          // LDX ZPY
      regX = memReadByte( popByte() + regY );
      if( regX ) regP &= 0xfd; else regP |= 0x02;
      if( regX & 0x80 ) regP |= 0x80; else regP &= 0x7f;
      break;
    case 0xb8:                          // CLV
      regP &= 0xbf;
      break;
    case 0xb9:                          // LDA ABSY
      addr = popWord() + regY;
      regA = memReadByte( addr );
      if( regA ) regP &= 0xfd; else regP |= 0x02;
      if( regA & 0x80 ) regP |= 0x80; else regP &= 0x7f;
      break;
    case 0xba:                          // TSX
      regX = regSP & 0xff;
      break;
    case 0xbc:                          // LDY ABSX
      addr = popWord() + regX;
      regY = memReadByte( addr );
      if( regY ) regP &= 0xfd; else regP |= 0x02;
      if( regY & 0x80 ) regP |= 0x80; else regP &= 0x7f;
      break;
    case 0xbd:                          // LDA ABSX
      addr = popWord() + regX;
      regA = memReadByte( addr );
      if( regA ) regP &= 0xfd; else regP |= 0x02;
      if( regA & 0x80 ) regP |= 0x80; else regP &= 0x7f;
      break;
    case 0xbe:                          // LDX ABSY
      addr = popWord() + regY;
      regX = memReadByte( addr );
      if( regX ) regP &= 0xfd; else regP |= 0x02;
      if( regX & 0x80 ) regP |= 0x80; else regP &= 0x7f;
      break;
    case 0xc0:                          // CPY IMM
      value = popByte();
      if( (regY+value) > 0xff ) regP |= 1; else regP &= 0xfe;
      ov = value;
      value = (regY-value);
      if( value ) regP &= 0xfd; else regP |= 0x02;
      if( value & 0x80 ) regP |= 0x80; else regP &= 0x7f;
      break;
    case 0xc1:                          // CMP INDY
      zp = popByte();
      addr = memReadByte(zp) + (memReadByte(zp+1)<<8) + regY;
      value = memReadByte( addr );
      doCompare( regA, value );
      break;
    case 0xc4:                          // CPY ZP
      value = memReadByte( popByte() );
      doCompare( regY, value );
      break;
    case 0xc5:                          // CMP ZP
      value = memReadByte( popByte() );
      doCompare( regA, value );
      break;
    case 0xc6:                          // DEC ZP
      zp = popByte();
      value = memReadByte( zp );
      --value;
      memStoreByte( zp, value&0xff );
      if( value ) regP &= 0xfd; else regP |= 0x02;
      if( value & 0x80 ) regP |= 0x80; else regP &= 0x7f;
      break;
    case 0xc8:                          // INY
      regY = (regY + 1) & 0xff;
      if( regY ) regP &= 0xfd; else regP |= 0x02;
      if( regY & 0x80 ) regP |= 0x80; else regP &= 0x7f;
      break;
    case 0xc9:                          // CMP IMM
      value = popByte();
      doCompare( regA, value );
      break;
    case 0xca:                          // DEX
      regX = (regX-1) & 0xff;
      if( regX ) regP &= 0xfd; else regP |= 0x02;
      if( regX & 0x80 ) regP |= 0x80; else regP &= 0x7f;
      break;
    case 0xcc:                          // CPY ABS
      value = memReadByte( popWord() );
      doCompare( regY, value );
      break;
    case 0xcd:                          // CMP ABS
      value = memReadByte( popWord() );
      doCompare( regA, value );
      break;
    case 0xce:                          // DEC ABS
      addr = popWord();
      value = memReadByte( addr );
      --value;
      value = value&0xff;
      memStoreByte( addr, value );
      if( value ) regP &= 0xfd; else regP |= 0x02;
      if( value & 0x80 ) regP |= 0x80; else regP &= 0x7f;
      break;
    case 0xd0:                          // BNE
      offset = popByte();
//      if( (regP&2)==0 ) { oldPC = regPC; jumpBranch( offset ); message( "Jumping from " + addr2hex(oldPC) + " to " + addr2hex(regPC) ); } else { message( "NOT jumping!" ); }
      if( (regP&2)==0 ) jumpBranch( offset );
      break;
    case 0xd1:                          // CMP INDY
      zp = popByte();
      addr = memReadByte(zp) + (memReadByte(zp+1)<<8) + regY;
      value = memReadByte( addr );
      doCompare( regA, value );
      break;
    case 0xd5:                          // CMP ZPX
      value = memReadByte( popByte() + regX );
      doCompare( regA, value );
      break;
    case 0xd6:                          // DEC ZPX
      addr = popByte() + regX;
      value = memReadByte( addr );
      --value;
      value = value&0xff;
      memStoreByte( addr, value );
      if( value ) regP &= 0xfd; else regP |= 0x02;
      if( value & 0x80 ) regP |= 0x80; else regP &= 0x7f;
      break;
    case 0xd8:                          // CLD (CLear Decimal)
      regP &= 0xf7;
      break;
    case 0xd9:                          // CMP ABSY
      addr = popWord() + regY;
      value = memReadByte( addr );
      doCompare( regA, value );
      break;
    case 0xdd:                          // CMP ABSX
      addr = popWord() + regX;
      value = memReadByte( addr );
      doCompare( regA, value );
      break;
    case 0xde:                          // DEC ABSX
      addr = popWord() + regX;
      value = memReadByte( addr );
      --value;
      value = value&0xff;
      memStoreByte( addr, value );
      if( value ) regP &= 0xfd; else regP |= 0x02;
      if( value & 0x80 ) regP |= 0x80; else regP &= 0x7f;
      break;
    case 0xe0:                          // CPX IMM
      value = popByte();
      doCompare( regX, value );
      break;
    case 0xe1:                          // SBC INDX
      zp = (popByte()+regX)&0xff;
      addr = memReadByte(zp) + (memReadByte(zp+1)<<8);
      value = memReadByte( addr );
      testSBC( value );
      break;
    case 0xe4:                          // CPX ZP
      value = memReadByte( popByte() );
      doCompare( regX, value );
      break;
    case 0xe5:                          // SBC ZP
      addr = popByte();
      value = memReadByte( addr );
      testSBC( value );
      break;
    case 0xe6:                          // INC ZP
      zp = popByte();
      value = memReadByte( zp );
      ++value;
      value = (value)&0xff;
      memStoreByte( zp, value );
      if( value ) regP &= 0xfd; else regP |= 0x02;
      if( value & 0x80 ) regP |= 0x80; else regP &= 0x7f;
      break;
    case 0xe8:                          // INX
      regX = (regX + 1) & 0xff;
      if( regX ) regP &= 0xfd; else regP |= 0x02;
      if( regX & 0x80 ) regP |= 0x80; else regP &= 0x7f;
      break;
    case 0xe9:                         // SBC IMM
      value = popByte();
      testSBC( value );
      break;
    case 0xea:                         // NOP
      break;
    case 0xec:                         // CPX ABS
      value = memReadByte( popWord() );
      doCompare( regX, value );
      break;
    case 0xed:                         // SBC ABS
      addr = popWord();
      value = memReadByte( addr );
      testSBC( value );
      break;
    case 0xee:                         // INC ABS
      addr = popWord();
      value = memReadByte( addr );
      ++value;
      value = (value)&0xff;
      memStoreByte( addr, value );
      if( value ) regP &= 0xfd; else regP |= 0x02;
      if( value & 0x80 ) regP |= 0x80; else regP &= 0x7f;
      break;
    case 0xf0:                         // BEQ
      offset = popByte();
      if( regP&2 ) jumpBranch( offset );
      break;
    case 0xf1:                         // SBC INDY
      zp = popByte();
      addr = memReadByte(zp) + (memReadByte(zp+1)<<8);
      value = memReadByte( addr + regY );
      testSBC( value );
      break;
    case 0xf5:                         // SBC ZPX
      addr = (popByte() + regX)&0xff;
      value = memReadByte( addr );
      regP = (regP&0xfe)|(value&1);
      testSBC( value );
      break;
    case 0xf6:                         // INC ZPX
      addr = popByte() + regX;
      value = memReadByte( addr );
      ++value;
      value=value&0xff;
      memStoreByte( addr, value );
      if( value ) regP &= 0xfd; else regP |= 0x02;
      if( value & 0x80 ) regP |= 0x80; else regP &= 0x7f;
      break;
    case 0xf8:                         // SED
      regP |= 8;
      break;
   case 0xf9:                          // SBC ABSY
      addr = popWord();
      value = memReadByte( addr + regY );
      testSBC( value );
      break;
    case 0xfd:                         // SBC ABSX
      addr = popWord();
      value = memReadByte( addr + regX );
      testSBC( value );
      break;
    case 0xfe: // INC ABSX
      addr = popWord() + regX;
      value = memReadByte( addr );
      ++value;
      value=value&0xff;
      memStoreByte( addr, value );
      if( value ) regP &= 0xfd; else regP |= 0x02;
      if( value & 0x80 ) regP |= 0x80; else regP &= 0x7f;
      break;
    default:
      message( "Address $" + addr2hex(regPC) + " - unknown opcode " + opcode );
      codeRunning = false;
      break;
  }

  if( (regPC == 0) || (!codeRunning) ) {
    clearInterval( myInterval );
    message( "Program end at PC=$" + addr2hex( regPC-1 ) );
    codeRunning = false;
    document.getElementById( "runButton" ).value = "Run";
    document.getElementById( "fileSelect" ).disabled = false;
    document.getElementById( "hexdumpButton" ).disabled = false;
//    updateDisplayFull();
  }
}

/*
 *  updatePixelDisplay() - Updates the display at one pixel position
 *
 */

function updateDisplayPixel( addr ) {
  display[addr-0x200].background = palette[memory[addr] & 0x0f];
}


/*
 *  updateDisplayFull() - Simply redraws the entire display according to memory
 *  The colors are supposed to be identical with the C64's palette.
 *
 */

function updateDisplayFull() {
  for( y=0; y<32; y++ ) {
    for( x=0; x<32; x++ ) {
      updateDisplayPixel( ((y<<5)+x) + 0x200 );
    }
  }
}