diff --git a/emulator/B5500CentralControl.js b/emulator/B5500CentralControl.js
index 4616652..7c03932 100644
--- a/emulator/B5500CentralControl.js
+++ b/emulator/B5500CentralControl.js
@@ -544,7 +544,7 @@ B5500CentralControl.prototype.tock = function tock() {
         *************************************/
     }
     interval = (that.nextTimeStamp += B5500CentralControl.rtcTick) - thisTime;
-    that.timer = setTimeout(function() {that.tock()}, (interval < 0 ? 1 : interval));
+    that.timer = setTimeout(that.tock, (interval < 0 ? 1 : interval));
 };
 
 /**************************************/
diff --git a/emulator/B5500Processor.js b/emulator/B5500Processor.js
index b8fcca1..4d92e3a 100644
--- a/emulator/B5500Processor.js
+++ b/emulator/B5500Processor.js
@@ -2590,7 +2590,7 @@ B5500Processor.prototype.applyRCW = function(word, inline) {
     this.V = f = word % 8;              //   [7:3], V
     word = (word-f)/8;
     this.H = word % 8;                  //   [4:3], H
-    word = (word - word % 0x10)/0x10;
+    word = (word - word % 16)/16;
     return word % 2;                    //   [2:1], DESC bit
 };
 
@@ -2634,9 +2634,8 @@ B5500Processor.prototype.enterSubroutine = function(descriptorCall) {
     /* Enters a subroutine via the present Program Descriptor in A as part
     of an OPDC or DESC syllable. Also handles accidental entry */
     var aw = this.A;                    // local copy of word in A reg
-    var bw;                             // local copy of word in B reg
     var arg = this.cc.bit(aw, 5);       // descriptor argument bit
-    var mode = this.cc.bit(aw, 4);      // descriptor mode bit (1-char mode)
+    var mode = this.cc.bit(aw, 4);      // descriptor mode bit (1=char mode)
 
     if (arg && !this.MSFF) {
         ; // just leave the Program Descriptor on TOS
@@ -2650,6 +2649,7 @@ B5500Processor.prototype.enterSubroutine = function(descriptorCall) {
             this.B = this.buildMSCW();
             this.BROF = 1;
             this.adjustBEmpty();
+            this.F = this.S;
         }
 
         // Push a RCW
@@ -2705,7 +2705,7 @@ B5500Processor.prototype.exitSubroutine = function(inline) {
         }
     } else {                            // flag bit is set
         result = this.applyRCW(this.B, inline);
-        this.X = this.B % 0x8000000000; // save F setting from MSCW to restore S at end
+        this.X = this.B % 0x8000000000; // save F setting from RCW to restore S at end
 
         this.S = this.F;
         this.loadBviaS();               // B = [S], fetch the MSCW
@@ -4496,6 +4496,7 @@ B5500Processor.prototype.run = function() {
         /***************************************************************
         *   SECL: Syllable Execution Complete Level                    *
         ***************************************************************/
+
         if ((this === this.cc.P1 ? this.cc.IAR : this.I) && this.NCSF) {
             // there's an interrupt and we're in normal state
             this.T = 0x0609;            // inject 3011=SFI into T
diff --git a/webUI/tools/B5500SyllableDebugger.html b/webUI/tools/B5500SyllableDebugger.html
index 98ddb2c..3797603 100644
--- a/webUI/tools/B5500SyllableDebugger.html
+++ b/webUI/tools/B5500SyllableDebugger.html
@@ -19,9 +19,12 @@
 <script>
 "use strict";
 
+const timerCycles = 1000;               // Number of instructions per pseudo-timer interrupt
+
 var cc;
 var injected = false;                   // true if syllable manually injected into T
 var memAddr = 0x40;                     // @100
+var runSilently = false;                // true if system state is not to be refreshed after each step
 var stopAddress = 0;                    // run-until-address stop point
 
 var accessor = {                        // Memory access control block
@@ -465,7 +468,7 @@ function displayNumber(id, value) {
     if (e) {
         setText(id, (Math.pow(8, e)*(s ? -m : m)).toPrecision(12));
     } else {
-        setText(id, m.toString());
+        setText(id, (s ? -m : m).toString());
     }
 }
 
@@ -686,26 +689,49 @@ function runIt(ev) {
     /* Steps through instructions continuously until the C register matches the
     StopAddr address. StopAddr can be changed while running. Setting it to zero
     (or blank) will halt the continuous stepping */
+    var count = timerCycles;
     var runBtn = $$("RunBtn");
     var saveStopAddress = stopAddress;
     var stopAddr = $$("StopAddr");
 
     function syllabicate() {
-        if (stopAddress && cc.P1.C != stopAddress) {
+        do {
             cc.P1.step();
-            displaySystemState();
-            if (isNaN(stopAddress)) {
-                stopAddress = 0;            // bad address
-                stopAddr.style.backgroundColor = "red";
-                runBtn.value = "Run";
-            } else {
-                setTimeout(syllabicate, 0);
+            if (cc.P1.S > 0x7FFF) {
+                alert("P1.S out of range");
+                stopAddress = 0;
             }
+            /***************************
+            if (cc.P1.R != 0) {
+                alert("P1.R not zero");
+                stopAddress = 0;
+            }
+            ***************************/
+            if (--count <= 0) {
+                count = timerCycles;
+                cc.CCI03F = 1;          // set timer interrupt
+                cc.signalInterrupt();
+                break;                  // exit loop to pick up events
+            }
+        } while (runSilently && stopAddress && cc.P1.C != stopAddress);
+
+        if (stopAddress && cc.P1.C != stopAddress) {
+            setTimeout(syllabicate, 0);
+            if (!runSilently) {
+                displaySystemState();
+            }
+        } else if (isNaN(stopAddress)) {
+            stopAddress = 0;            // bad address
+            stopAddr.style.backgroundColor = "red";
+            runBtn.value = "Run";
         } else {
             stopAddress = saveStopAddress;
             stopAddr.style.backgroundColor = "";
             stopAddr.value = padOctal(stopAddress, stopAddr.maxLength);
             runBtn.value = "Run";
+            if (runSilently) {
+                displaySystemState();
+            }
         }
     }
 
@@ -788,6 +814,12 @@ function tos_onChange(ev, bicID, valueID, origID) {
     return value;
 }
 
+function runSilently_onClick(ev) {
+    /* Handle the onchange event for the RunSilently checkbox */
+
+    runSilently = ev.target.checked;
+}
+
 function fileLoader_onLoad(ev) {
     /* Handle the onload event for an ArrayBuffer FileReader */
     var addr = 0;                   // starting B5500 memory address
@@ -996,6 +1028,7 @@ function initialize() {
     $$("GoBtn").addEventListener("click", goIt, false);
     $$("StepBtn").addEventListener("click", stepIt, false);
     $$("RunBtn").addEventListener("click", runIt, false);
+    $$("RunSilently").addEventListener("click", runSilently_onClick, false);
 
     cc = new B5500CentralControl();
     cc.powerOn();
@@ -1014,6 +1047,7 @@ function initialize() {
 
     displaySystemState();
     displayOctal("StopAddr", stopAddress, 5);
+    $$("RunSilently").checked = runSilently;
 }
 
 window.onload = function() {
@@ -1040,6 +1074,11 @@ window.onload = function() {
 </p>
 
 <table id=RegisterBank1 class="normal border">
+<colgroup>
+    <col span=4>
+    <col style="width:12em">
+    <col>
+</colgroup>
 <thead>
 <tr>
     <th>Reg
@@ -1232,6 +1271,14 @@ window.onload = function() {
 </table>
 
 <table id=RegisterBank2 class="normal border">
+<colgroup>
+    <col style="width:2em">
+    <col style="width:10em">
+    <col style="width:2em">
+    <col style="width:7em">
+    <col style="width:2em">
+    <col style="width:7em">
+</colgroup>
 <tbody>
 <tr>
     <td class=center>X
@@ -1327,6 +1374,10 @@ window.onload = function() {
         <input id=StopAddr name=StopAddr type=text class=number size=5 maxlength=5>
         &nbsp;
         <input id=RunBtn name=RunBtn type=button value="Run" accesskey=R>
+<tr>
+    <td colspan=6 class=rj>
+        <label for=RunSilently>Run Silently</label>
+        <input id=RunSilently name=RunSilently type=checkbox value=1>
 </table>
 
 <table id=CentralControl>