การนำค่าที่ส่งกลับจาก ajax มาสร้างตัวแปรใน php เพื่อนำไปใช้งานครับ

<select name="menu1"  id="menu1" onChange="startCalc();JavaScript:doCallAjax();" onBlur="stopCalc();" >
<option value=""></option>
<?
for($i=0;$i<count($result_of_intersect);$i++)
{
?>
<option value="<?=$result_of_intersect3["$i"];?><? echo "|";?><?=$result_of_intersect2["$i"];?>"><?=$result_of_intersect["$i"];?></option>	   
<?
}
?>
</select>  

<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 = "tUsercalnet=" + encodeURI( document.getElementById("usercalnet").value) +
						"&tMenu1=" + encodeURI( document.getElementById("menu1").value ) +
						"&tMenu2=" + encodeURI( document.getElementById("menu2").value ) +
						"&tMenu3=" + encodeURI( document.getElementById("menu3").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;
						document.frmMain.txtName.value=HttPRequest.responseText; //แสดงที่ textbox  txtName ดังรูป
						var value = HttPRequest.responseText;
						eval(value);
						//alert (value); 
					}
				}
			}
	   }
	</script>

<?php
	$strUsercalnet = trim($_POST["tUsercalnet"]);
	$strMenu1  = trim($_POST["tMenu1"]);   $mmenu1   = explode ("|", $strMenu1);
	$strMenu2  = trim($_POST["tMenu2"]);   $mmenu2   = explode ("|", $strMenu2);
	$strMenu3  = trim($_POST["tMenu3"]);   $mmenu3   = explode ("|", $strMenu3);

	$value = $strUsercalnet - ($mmenu1[0] + $mmenu2[0] + $mmenu3[0] );
	echo "$value";
?>

document.frmMain.txtName.value=HttPRequest.responseText;