สอบถามการรับค่าคืนจาก AJAX เพื่อนำตัวแปรดังกล่าวมาใช้งานใน PHP ครับ

<script language="JavaScript">
	   var HttPRequest = false;

	   function doCallAjax() {
		  HttPRequest = false;
		  if (window.XMLHttpRequest) { // Mozilla, Safari,...
			 HttPRequest = new XMLHttpRequest();
			 if (HttPRequest.overrideMimeType) {
				HttPRequest.overrideMimeType('text/html');
			 }
		  } else if (window.ActiveXObject) { // IE
			 try {
				HttPRequest = new ActiveXObject("Msxml2.XMLHTTP");
			 } catch (e) {
				try {
				   HttPRequest = new ActiveXObject("Microsoft.XMLHTTP");
				} catch (e) {}
			 }
		  } 
		  
		  if (!HttPRequest) {
			 alert('Cannot create XMLHTTP instance');
			 return false;
		  }
	
		  var url = '../food/modules/mealtable/chkcalorie.php';
		  
		  var pmeters = "tUserperweek=" + encodeURI( document.getElementById("userperweek").value) +
						"&tMenu1=" + encodeURI( document.getElementById("menu1").value );
		  

			HttPRequest.open('POST',url,true);

			HttPRequest.setRequestHeader("Content-type", "application/x-www-form-urlencoded");
			HttPRequest.setRequestHeader("Content-length", pmeters.length);
			HttPRequest.setRequestHeader("Connection", "close");
			HttPRequest.send(pmeters);
			
			
			HttPRequest.onreadystatechange = function()
			{

				if(HttPRequest.readyState == 3)  // Loading Request
				{
					document.getElementById("mySpan").innerHTML = "..";
				}

				if(HttPRequest.readyState == 4) // Return Request
				{
					if(HttPRequest.responseText == 'Y')
					{
						window.location = 'AjaxPHPRegister3.php';
					}
					else
					{
						document.getElementById("mySpan").innerHTML = HttPRequest.responseText;
						var js = HttPRequest.responseText;
						//alert (js);
					}
				}
				
			}

	   }
	</script>

<?php
	
	$strUserperweek = trim($_POST["tUserperweek"]);
	$strMenu1  = trim($_POST["tMenu1"]);   $mmenu1   = explode ("|", $strMenu1);

	$ABC = $strUserperweek - ($mmenu1[0]);
	echo "$ABC";
?>