code: function() {
  		this.prgBanks = this.header[4];
  		this.chrBanks = this.header[5];
  		this.ramBanks = this.header[8] || 1;
  
  		this.prgSize = this.prgBanks * 16 * 1024;
  		this.chrSize = this.chrBanks * 8 * 1024;
  		this.ramSize = this.ramBanks * 8 * 1024;
  
  		this.prgData = this.data.subarray( 0, this.prgSize );
  
  		if ( this.chrBanks ) {
  			this.chrData = this.data.subarray( this.prgSize, this.prgSize + this.chrSize );
  		} else {
  			// no CHR banks, but probably still CHR RAM
  			this.chrData = new Uint8Array( 0x2000 );
  		}
  
  		this.ramData = new Uint8Array( this.ramSize );
  
  		this.initMapper();
  	}
docs: Init prg/chr/ram data.