diff --git a/emulator/B5500CentralControl.js b/emulator/B5500CentralControl.js
index dfe6fc0..1885255 100644
--- a/emulator/B5500CentralControl.js
+++ b/emulator/B5500CentralControl.js
@@ -64,10 +64,10 @@ function B5500CentralControl(global) {
 /**************************************/
     /* Global constants */
 
-B5500CentralControl.version = "0.15";
+B5500CentralControl.version = "0.16";
 
-B5500CentralControl.memReadCycles = 1.8;        // assume 2 µs memory read cycle time (the other option was 3 µs)
-B5500CentralControl.memWriteCycles = 2.5;       // assume 4 µs memory write cycle time (the other option was 6 µs)
+B5500CentralControl.memReadCycles = 2;          // assume 2 µs memory read cycle time (the other option was 3 µs)
+B5500CentralControl.memWriteCycles = 3;         // assume 4 µs memory write cycle time (the other option was 6 µs)
 B5500CentralControl.rtcTick = 1000/60;          // Real-time clock period, milliseconds
 
 B5500CentralControl.pow2 = [ // powers of 2 from 0 to 52
diff --git a/emulator/B5500IOUnit.js b/emulator/B5500IOUnit.js
index 961d5d5..260f1aa 100644
--- a/emulator/B5500IOUnit.js
+++ b/emulator/B5500IOUnit.js
@@ -780,14 +780,13 @@ B5500IOUnit.prototype.finishDatacomRead = function finishDatacomRead(errorMask,
     var bufExhausted = (errorMask & 0x080) >>> 7;
     var tuBuf = (errorMask%0x10000000000 - errorMask%0x40000000)/0x40000000;    // get TU/buf #
 
-    if (length > 0) {
-        if (bufExhausted || (tuBuf & 0x10)) {
-            this.storeBuffer(length, 0, 1, 56);
-        } else {
-            this.storeBufferWithGM(length, 0, 1, 56);
-        }
-        this.Daddress += (length+7) >>> 3;
+    if (bufExhausted || (tuBuf & 0x10)) {
+        this.storeBuffer(length, 0, 1, 56);
+    } else {
+        this.storeBufferWithGM(length, 0, 1, 56);
     }
+    this.Daddress += (length+7) >>> 3;
+
     // Decode the additional datacom status/error bits
     this.D25F = bufExhausted;
     this.D24F = (errorMask & 0x100) >>> 8;
@@ -802,9 +801,10 @@ B5500IOUnit.prototype.finishDatacomWrite = function finishDatacomWrite(errorMask
     var bufExhausted = (errorMask & 0x080) >>> 7;
     var tuBuf = (errorMask%0x10000000000 - errorMask%0x40000000)/0x40000000;    // get TU/buf #
 
-    if (length > 0) {
-        this.Daddress += (length+7) >>> 3;
+    if (!(bufExhausted || (this.DwordCount & 0x10))) {
+        length++;                       // account for the terminating Group Mark
     }
+    this.Daddress += (length+7) >>> 3;
 
     // Decode the additional datacom status/error bits
     this.D25F = bufExhausted;
diff --git a/webUI/B5500CardReader.js b/webUI/B5500CardReader.js
index b9bdb4f..38375d5 100644
--- a/webUI/B5500CardReader.js
+++ b/webUI/B5500CardReader.js
@@ -184,6 +184,7 @@ B5500CardReader.prototype.CRProgressBar_onclick = function CRProgressBar_onclick
             this.bufLength = 0;
             this.bufIndex = 0;
             this.progressBar.value = 0;
+            this.$$("CRFileSelector").value = null;     // reset the control
             while (this.outHopper.childNodes.length > 0) {
                 this.outHopper.removeChild(this.outHopper.firstChild);
             }
diff --git a/webUI/B5500DatacomUnit.css b/webUI/B5500DatacomUnit.css
index 592c385..f663e13 100644
--- a/webUI/B5500DatacomUnit.css
+++ b/webUI/B5500DatacomUnit.css
@@ -44,6 +44,7 @@ BUTTON.greenButton {
     border-radius:      4px}
 
 BUTTON.greenLit {
+    color:              black;
     background-color:   #0F0}
 
 BUTTON.blackBorder {
diff --git a/webUI/B5500DatacomUnit.js b/webUI/B5500DatacomUnit.js
index 6f2b633..eafc428 100644
--- a/webUI/B5500DatacomUnit.js
+++ b/webUI/B5500DatacomUnit.js
@@ -29,7 +29,7 @@ function B5500DatacomUnit(mnemonic, unitIndex, designate, statusChange, signal)
 
     this.maxScrollLines = 1500;         // Maximum amount of printer scrollback
     this.charPeriod = 100;              // Printer speed, milliseconds per character
-    this.bufferSize = 112;              // 4 B487 buffer segments
+    this.bufferSize = 112;              // 4 28-character B487 buffer segments
 
     this.mnemonic = mnemonic;           // Unit mnemonic
     this.unitIndex = unitIndex;         // Ready-mask bit number
@@ -247,14 +247,13 @@ B5500DatacomUnit.prototype.appendEmptyLine = function appendEmptyLine() {
     /* Removes excess lines already printed, then appends a new <pre> element
     to the <iframe>, creating an empty text node inside the new element */
     var count = this.paper.childNodes.length;
-    var line = this.doc.createTextNode("");
 
     while (count-- > this.maxScrollLines) {
         this.paper.removeChild(this.paper.firstChild);
     }
     this.paper.lastChild.nodeValue += String.fromCharCode(0x0A);        // newline
     this.endOfPaper.scrollIntoView();
-    this.paper.appendChild(line);
+    this.paper.appendChild(this.doc.createTextNode(""));
 };
 
 /**************************************/
@@ -350,7 +349,7 @@ B5500DatacomUnit.prototype.terminateInput = function terminateInput() {
 
 /**************************************/
 B5500DatacomUnit.prototype.keyPress = function keyPress(ev) {
-    /* Handles keyboard character events. Depending on the state of the unit,
+    /* Handles keyboard character events. Depending on the state of the buffer,
     either buffers the character for transmission to the I/O Unit, echos
     it to the printer, or ignores it altogether */
     var c = ev.charCode;
@@ -407,14 +406,17 @@ B5500DatacomUnit.prototype.keyPress = function keyPress(ev) {
         if (this.bufState == this.bufReadReady && this.fullBuffer) {
             this.interrupt = true;
             this.setState(this.bufInputBusy);
-            this.signal();              // buffer overflow
+            setCallback(this.signal, this, delay);      // buffer overflow
+            ev.stopPropagation();
+            ev.preventDefault();
         } else if (this.bufState == this.bufInputBusy || this.bufState == this.bufIdle) {
             switch (c) {
             case 0x7E:                  // ~ left-arrow (Group Mark), end of message
                 this.inTimer = setCallback(this.printChar, this, delay, c);
-                this.nextCharTime = nextTime;
-                this.terminateInput();
+                this.nextCharTime = this.charPeriod + nextTime;
+                setCallback(this.terminateInput, this, this.charPeriod+delay);
                 ev.stopPropagation();
+                ev.preventDefault();
                 break;
             case 0x3C:                  // <, backspace
                 if (this.bufIndex > 0) {
@@ -423,40 +425,41 @@ B5500DatacomUnit.prototype.keyPress = function keyPress(ev) {
                 this.inTimer = setCallback(this.printChar, this, delay, c);
                 this.nextCharTime = nextTime;
                 ev.stopPropagation();
+                ev.preventDefault();
                 break;
             case 0x21:                  // ! EOT, disconnect
-                //this.buffer[this.bufIndex++] = 0x7D;    // } greater-or-equal code
+                this.buffer[this.bufIndex++] = 0x7D;    // } greater-or-equal code
                 this.interrupt = true;
                 this.abnomal = true;
                 this.setState(this.bufReadReady);
-                this.signal();
+                setCallback(this.signal, this, delay);
                 this.inTimer = setCallback(this.printChar, this, delay, c);
                 this.nextCharTime = nextTime;
                 ev.stopPropagation();
+                ev.preventDefault();
                 break;
-            case 0x02:                  // Ctrl-B, STX, break on output
-                if (this.bufState == this.bufOutputBusy) {
-                    this.interrupt = true;
-                    this.abnormal = true;
-                    this.setState(this.bufReadReady);
-                    this.signal();
-                } else if (this.bufState == this.bufInputBusy) {
-                    this.bufIndex = this.bufLength = 0;
-                    this.setState(this.bufIdle);
-                }
+            case 0x02:                  // Ctrl-B, STX, break on input
+                this.bufIndex = this.bufLength = 0;
+                this.setState(this.bufIdle);
+                ev.stopPropagation();
+                ev.preventDefault();
                 break;
             case 0x05:                  // Ctrl-E, ENQ, who-are-you (WRU)
                 if (this.bufState == this.bufIdle || this.bufState == this.bufInputBusy) {
                     this.interrupt = true;
                     this.abnormal = true;
                     this.setState(this.bufWriteReady);
-                    this.signal();
+                    setCallback(this.signal, this, delay);
                 }
+                ev.stopPropagation();
+                ev.preventDefault();
                 break;
             case 0x0C:                  // Ctrl-L, FF, clear input buffer
                 if (this.bufState == this.bufInputBusy) {
                     this.bufIndex = this.bufLength = 0;
                 }
+                ev.stopPropagation();
+                ev.preventDefault();
                 break;
             case 0x3F:                  // ? question-mark, set abnormal for control message
                 this.abnormal = true;
@@ -468,96 +471,28 @@ B5500DatacomUnit.prototype.keyPress = function keyPress(ev) {
                     this.buffer[this.bufIndex++] = c;
                     this.inTimer = setCallback(this.printChar, this, delay, c);
                     this.nextCharTime = nextTime;
-                    ev.stopPropagation();
                     if (this.bufIndex < this.bufferSize) {
                         this.setState(this.bufInputBusy);
                     } else {
                         this.interrupt = true;
                         this.fullBuffer = true;
                         this.setState(this.bufReadReady);
-                        this.signal();  // full buffer, no GM detected
+                        setCallback(this.signal, this, this.charPeriod+delay);  // full buffer, no GM detected
                     }
+                    ev.stopPropagation();
+                    ev.preventDefault();
                 }
                 break;
-            }
-        }
-
-        ev.preventDefault();
-    }
-};
-
-/**************************************/
-B5500DatacomUnit.prototype.keyDown = function keyDown(ev) {
-    /* Handles key-down events to capture Ctrl-E (ENQ), Ctrl-L (FF), Ctrl-Q (DC1),
-    and Enter keystrokes */
-    var c = ev.keyCode;
-    var delay;
-    var nextTime;
-    var result = true;
-    var stamp;
-
-    //this.$$("KeyCode").innerHTML = "KC " + c.toString() + ":0x" + c.toString(16) +
-    //    (ev.shiftKey ? "S" : " ") + (ev.ctrlKey ? "C" : " ") + (ev.altKey ? "A" : " ");
-
-    if (this.connected) {
-        stamp = new Date().getTime();
-        nextTime = (this.nextCharTime < stamp ? stamp : this.nextCharTime) + this.charPeriod;
-        delay = nextTime - stamp;
-
-        switch (c) {
-        case 0x08:                      // Backspace
-            if (this.bufState == this.bufInputBusy) {
-                if (this.bufIndex > 0) {
-                    this.bufIndex--;
-                }
-                this.inTimer = setCallback(this.printChar, this, delay, 0x3C);
-                this.nextCharTime = nextTime;
-            }
-            break;
-        case 0x0D:                      // Enter
-        //case 0x11:                      // Ctrl-Q, DC1 (X-ON)
-            if (this.bufState == this.bufInputBusy || this.bufState == this.bufIdle) {
-                this.inTimer = setCallback(this.printChar, this, delay, 0x7E);
-                this.nextCharTime = nextTime;
-                this.terminateInput();
-                ev.preventDefault();
-                ev.stopPropagation();
-                break;
-            }
-            break;
-        case 0x02:                      // Ctrl-B, STX, break on output
-            if (this.bufState == this.bufOutputBusy) {
+            } // switch c
+        } else if (this.bufState == this.bufOutputBusy) {
+            if (c == 0x02) {            // Ctrl-B, STX, break on output
                 this.interrupt = true;
                 this.abnormal = true;
                 this.setState(this.bufReadReady);
-                this.signal();
-            } else if (this.bufState == this.bufInputBusy) {
-                this.bufIndex = this.bufLength = 0;
-                this.setState(this.bufIdle);
+                setCallback(this.signal, this, delay);
+                ev.stopPropagation();
+                ev.preventDefault();
             }
-            break;
-        case 0x05:                      // Ctrl-E, ENQ, who-are-you (WRU)
-            if (this.bufState == this.bufIdle || this.bufState == this.bufInputBusy) {
-                this.interrupt = true;
-                this.abnormal = true;
-                this.setState(this.bufWriteReady);
-                this.signal();
-            }
-            break;
-        case 0x0C:                      // Ctrl-L, FF, clear input buffer
-            if (this.bufState == this.bufInputBusy) {
-                this.bufIndex = this.bufLength = 0;
-            }
-            break;
-        default:
-            result = false;
-            break;
-        }
-
-        this.showBufferIndex();
-        if (result) {
-            ev.preventDefault();
-            ev.stopPropagation();
         }
     }
 };
@@ -590,7 +525,7 @@ B5500DatacomUnit.prototype.datacomOnload = function datacomOnload() {
     var x;
 
     this.doc = this.window.document;
-    this.doc.title = "retro-B5500 " + this.mnemonic + " TU1/BUF0";
+    this.doc.title = "retro-B5500 " + this.mnemonic + ": TU/BUF=01/00";
     this.paper = this.doc.createElement("pre");
     this.paper.appendChild(this.doc.createTextNode(""));
     this.$$("TermOut").contentDocument.body.appendChild(this.paper);
@@ -641,13 +576,13 @@ B5500DatacomUnit.prototype.read = function read(finish, buffer, length, mode, co
         this.errorMask |= 0x34;         // not connected -- set buffer not ready
         break;
     case this.bufState == this.bufReadReady:
-        // Copy the adaptor buffer to the IOUnit buffer
+        // Copy the adapter buffer to the IOUnit buffer
         actualLength = (transparent ? this.bufferSize : this.bufIndex);
         for (x=0; x<actualLength; x++) {
             buffer[x] = this.buffer[x];
         }
 
-        // Set the state bits in the result and reset the adaptor to idle
+        // Set the state bits in the result and reset the adapter to idle
         if (this.abnormal) {
             this.errorMask |= 0x200;    // set abnormal bit
         }
@@ -803,9 +738,14 @@ B5500DatacomUnit.prototype.writeInterrogate = function writeInterrogate(finish,
         this.errorMask |= 0x34;         // not a valid TU/BUF -- report not ready
     } else if (tuNr == 1 && bufNr > 0) {
         this.errorMask |= 0x34          // not a valid BUF for TU#1 -- report not ready
-    } else if (this.interrupt) {
-        tuNr = 1;                       // it must be for TU=1, BUF=0
-        bufNr = 0;
+    } else if (tuNr == 0) {
+        if (this.interrupt) {
+            tuNr = 1;
+            bufNr = 0;
+        }
+    }
+
+    if (tuNr == 1 && bufNr == 0) {
         switch (this.bufState) {
         case this.bufReadReady:
             this.errorMask |= 0x100;
diff --git a/webUI/B5500MagTapeDrive.js b/webUI/B5500MagTapeDrive.js
index ea6d8e3..f09c12c 100644
--- a/webUI/B5500MagTapeDrive.js
+++ b/webUI/B5500MagTapeDrive.js
@@ -218,7 +218,7 @@ B5500MagTapeDrive.prototype.setAtEOT = function setAtEOT(atEOT) {
 B5500MagTapeDrive.prototype.setTapeUnloaded = function setTapeUnloaded() {
     /* Controls the loaded/unloaded-state of the tape drive */
 
-    if (this.tapeState != this.tapeRemote) {
+    if (this.tapeState == this.tapeLocal && this.atBOT) {
         this.tapeState = this.tapeUnloaded;
         this.image = null;                  // release the tape image to GC
         this.imgIndex = this.imgLength = 0;
@@ -298,7 +298,8 @@ B5500MagTapeDrive.prototype.setWriteRing = function setWriteRing(writeRing) {
 B5500MagTapeDrive.prototype.tapeRewind = function tapeRewind(makeReady) {
     /* Rewinds the tape. Makes the drive not-ready and delays for an appropriate amount
     of time depending on how far up-tape we are. If makeReady is true, then readies
-    the unit again when the rewind is complete (valid only from this.rewind()) */
+    the unit again when the rewind is complete [valid only when called from
+    this.rewind()] */
     var inches;
     var inchFactor = this.imgIndex/this.tapeInches;
     var lastStamp = new Date().getTime();
@@ -307,8 +308,11 @@ B5500MagTapeDrive.prototype.tapeRewind = function tapeRewind(makeReady) {
         var stamp = new Date().getTime();
         var interval = stamp - lastStamp;
 
+        if (interval <= 0) {
+            interval = 1;
+        }
         if (this.tapeInches > 0) {
-            inches = interval/1000*this.rewindSpeed + 1;
+            inches = interval/1000*this.rewindSpeed;
             this.tapeInches -= inches;
             this.spinReel(-inches);
             this.progressBar.value = this.imgLength - this.tapeInches*inchFactor;
@@ -333,7 +337,7 @@ B5500MagTapeDrive.prototype.tapeRewind = function tapeRewind(makeReady) {
         this.setAtEOT(false);
         this.addClass(this.$$("MTRewindingLight"), "whiteLit");
         this.timer = setCallback(rewindDelay, this,
-                this.startStopTime*1000 + this.initiateStamp - new Date().getTime());
+                this.startStopTime*1000 + this.initiateStamp - lastStamp);
     }
 };
 
@@ -772,16 +776,12 @@ B5500MagTapeDrive.prototype.read = function read(finish, buffer, length, mode, c
             count = this.bcdReadBackward(mode);
             residue = 7 - count % 8;
             imgCount -= this.imgIndex;
-            if (imgCount > 0) {
-                inches = -imgCount/this.density - this.gapLength;
-            }
+            inches = -imgCount/this.density - this.gapLength;
         } else {
             count = this.bcdReadForward(mode);
             residue = count % 8;
             imgCount = this.imgIndex - imgCount;
-            if (imgCount > 0) {
-                inches = imgCount/this.density + this.gapLength;
-            }
+            inches = imgCount/this.density + this.gapLength;
         }
 
         this.tapeInches += inches;
@@ -800,7 +800,7 @@ B5500MagTapeDrive.prototype.read = function read(finish, buffer, length, mode, c
         }
         this.buffer = null;
     }
-    //console.log(this.mnemonic + " read: c=" + control + ", length=" + length + ", mode=" + mode +
+    //console.log(this.mnemonic + " read:             c=" + control + ", length=" + length + ", mode=" + mode +
     //    ", count=" + count + ", inches=" + this.tapeInches +
     //    ", index=" + this.imgIndex + ", mask=" + this.errorMask.toString(8));
     //console.log(String.fromCharCode.apply(null, buffer.subarray(0, 80)).substring(0, count));
@@ -827,15 +827,11 @@ B5500MagTapeDrive.prototype.space = function space(finish, length, control) {
         if (control) {
             this.bcdSpaceBackward(true);
             imgCount -= this.imgIndex;
-            if (imgCount > 0) {
-                inches = -imgCount/this.density - this.gapLength;
-            }
+            inches = -imgCount/this.density - this.gapLength;
         } else {
             this.bcdSpaceForward(true);
             imgCount = this.imgIndex - imgCount;
-            if (imgCount > 0) {
-                inches = imgCount/this.density + this.gapLength;
-            }
+            inches = imgCount/this.density + this.gapLength;
         }
 
         this.tapeInches += inches;
@@ -853,7 +849,7 @@ B5500MagTapeDrive.prototype.space = function space(finish, length, control) {
             this.progressBar.value = 0;
         }
     }
-    //console.log(this.mnemonic + " space: c=" + control + ", length=" + length +
+    //console.log(this.mnemonic + " space:           c=" + control + ", length=" + length +
     //    ", count=" + imgCount + ", inches=" + this.tapeInches +
     //    ", index=" + this.imgIndex + ", mask=" + this.errorMask.toString(8));
 };
@@ -889,7 +885,7 @@ B5500MagTapeDrive.prototype.rewind = function rewind(finish) {
         this.buildErrorMask(0);
         finish(this.errorMask, 0);
     }
-    //console.log(this.mnemonic + " rewind: mask=" + this.errorMask.toString(8));
+    //console.log(this.mnemonic + " rewind:           mask=" + this.errorMask.toString(8));
 };
 
 /**************************************/
diff --git a/webUI/B5500SPOUnit.css b/webUI/B5500SPOUnit.css
index adf3a63..6d63099 100644
--- a/webUI/B5500SPOUnit.css
+++ b/webUI/B5500SPOUnit.css
@@ -60,7 +60,7 @@ BUTTON.greenButton {
     color:              black;
     font-family:        Arial Rounded, Arial, Helvetica, sans-serif;
     font-size:          8pt;
-    font-weight:        bold;
+    font-weight:        normal;
     width:              60px;
     height:             40px;
     border:             1px solid black;
@@ -72,7 +72,7 @@ BUTTON.yellowButton {
     color:              black;
     font-family:        Arial Rounded, Arial, Helvetica, sans-serif;
     font-size:          8pt;
-    font-weight:        bold;
+    font-weight:        normal;
     width:              60px;
     height:             40px;
     border:             1px solid black;
diff --git a/webUI/B5500SPOUnit.js b/webUI/B5500SPOUnit.js
index 08f485b..639954b 100644
--- a/webUI/B5500SPOUnit.js
+++ b/webUI/B5500SPOUnit.js
@@ -153,17 +153,16 @@ B5500SPOUnit.prototype.setRemote = function setRemote() {
 
 /**************************************/
 B5500SPOUnit.prototype.appendEmptyLine = function appendEmptyLine() {
-    /* Removes excess lines already printed, then appends a new <pre> element
-    to the <iframe>, creating an empty text node inside the new element */
+    /* Removes excess lines already printed, then appends a new text node
+    to the <pre> element within the <iframe> */
     var count = this.paper.childNodes.length;
-    var line = this.doc.createTextNode("");
 
     this.printChar(0x0A);               // newline
     while (count-- > this.maxScrollLines) {
         this.paper.removeChild(this.paper.firstChild);
     }
     this.endOfPaper.scrollIntoView();
-    this.paper.appendChild(line);
+    this.paper.appendChild(this.doc.createTextNode(""));
     this.printCol = 0;
 };
 
@@ -459,7 +458,7 @@ B5500SPOUnit.prototype.read = function read(finish, buffer, length, mode, contro
         this.bufIndex = 0;
         this.nextCharTime = new Date().getTime();
         this.finish = finish;
-        //this.window.focus();          // interferes with datacom terminal window
+        this.window.focus();
         break;
     case this.spoOutput:
     case this.spoInput: