 & 0x00F;
		var x   = (this.m[this.pc  ]     ) & 0x00F;
		var y   = (this.m[this.pc+1] >> 4) & 0x00F;
		var n   = (this.m[this.pc+1]     ) & 0x00F;
		var nn  = (this.m[this.pc+1]     ) & 0x0FF;
		var nnn = op & 0xFFF;
		this.pc += 2;

		// execute a simple opcode
		if (op == 0x00E0) {
			// clear
			for(var layer = 0; layer < 2; layer++) {
				if ((this.plane & (layer+1)) == 0) { continue; }
				for(var z = 0; z < this.p[layer].length; z++) {
					this.p[layer][z] = 0;
				}
			}
			return;
		}
		if (op == 