diff --git a/macros.js b/macros.js
index cda8ba2..d50a916 100644
--- a/macros.js
+++ b/macros.js
@@ -29,20 +29,31 @@ var trace = Array();
 var logstream = Array();
 var running = false;
 
-function go(n){
+function loadProgram(){
+	if(userCode.length!=0)
+		code=userCode;
+	// default reset vector will be 0x0000 because undefined memory reads as zero
+	if(userResetLow!=undefined)
+		mWrite(0xfffc, userResetLow);
+	if(userResetHigh!=undefined)
+		mWrite(0xfffd, userResetHigh);
 	for(var i=0;i<code.length;i++){
 		mWrite(i, code[i]);
-		setCellValue(i, code[i]);
+		if(i<0x200)
+			setCellValue(i, code[i]);
 	}
-	mWrite(0xfffc, 0x00);
-	mWrite(0xfffd, 0x00);
-	steps();
 }
 
-function steps(){
+function go(){
+	if(userSteps!=undefined){
+		if(--userSteps==0){
+			running=false;
+			userSteps=undefined;
+		}
+	}
 	if(running) {
            step();
-	   setTimeout(steps, 0); // schedule the next poll
+	   setTimeout(go, 0); // schedule the next poll
         }
 }
 
@@ -99,7 +110,7 @@ function initChip(){
 	recalcNodeList(allNodes()); 
 	for(var i=0;i<8;i++){setHigh('clk0'), setLow('clk0');}
 	setHigh('res');
-	for(var i=0;i<18;i++){halfStep();}
+	for(var i=0;i<18;i++){halfStep();} // avoid updating graphics and trace buffer before user code
 	refresh();
 	cycle = 0;
 	trace = Array();
@@ -284,7 +295,7 @@ function runChip(){
 	start.style.visibility = 'hidden';
 	stop.style.visibility = 'visible';
 	running = true;
-        steps();
+        go();
 }
 
 function stopChip(){
diff --git a/memtable.js b/memtable.js
index 7f0c41c..bdeab3d 100644
--- a/memtable.js
+++ b/memtable.js
@@ -59,7 +59,9 @@ function cellKeydown(e){
 }
 
 function setCellValue(n, val){
-	val%=256; 
+	if(val==undefined)
+		val=0x00;
+	val%=256;
 	cellEl(n).val=val;
 	cellEl(n).innerHTML=hexByte(val);
 }
diff --git a/wires.js b/wires.js
index 6e23972..5c27a83 100644
--- a/wires.js
+++ b/wires.js
@@ -44,6 +44,10 @@ var moveHereFirst;
 var expertMode=false
 var animateChipLayout = true;
 var chipLayoutIsVisible = true;
+var userCode=[];
+var userResetLow;
+var userResetHigh;
+var userSteps;
 
 /////////////////////////
 //
@@ -78,6 +82,7 @@ function setup_part2(){
 function setup_part3(){
 	setupTable();
 	setupNodeNameList();
+	loadProgram();
 	initChip();
 	document.getElementById('stop').style.visibility = 'hidden';
 	go();
@@ -90,6 +95,7 @@ function setupParams(){
 	var panx;
 	var pany;
 	var zoom;
+	var userAddress;
 	for(var i=0;i<queryParts.length;i++){
 		var params=queryParts[i].split("=");
 		if(params.length!=2){
@@ -112,6 +118,17 @@ function setupParams(){
 			pany=parseInt(value);
 		} else if(name=="zoom" && parseInt(value)!=NaN){
 			zoom=parseInt(value);
+		} else if(name=="steps" && parseInt(value)!=NaN){
+			userSteps=parseInt(value);
+			running=true;
+		} else if(name=="a" && parseInt(value,16)!=NaN){
+			userAddress=parseInt(value,16);
+		} else if(name=="d" && value.match(/[0-9a-fA-F]*/)[0].length==value.length){
+			for(var j=0;j<value.length;j+=2)
+				userCode[userAddress++]=parseInt(value.slice(j,j+2),16);
+		} else if(name=="r" && parseInt(value,16)!=NaN){
+			userResetLow=parseInt(value,16)%256;
+			userResetHigh=(parseInt(value,16)>>8)%256;
 		} else {
 			if(loglevel>0)
 				console.log('unrecognised parameters:',params);