diff --git a/src/main/java/de/neemann/digital/core/memory/DataField.java b/src/main/java/de/neemann/digital/core/memory/DataField.java
index aad49c1e0..ee94c24d4 100644
--- a/src/main/java/de/neemann/digital/core/memory/DataField.java
+++ b/src/main/java/de/neemann/digital/core/memory/DataField.java
@@ -3,6 +3,7 @@ package de.neemann.digital.core.memory;
 import de.neemann.digital.lang.Lang;
 
 import java.io.*;
+import java.util.ArrayList;
 import java.util.Arrays;
 
 /**
@@ -10,22 +11,26 @@ import java.util.Arrays;
  */
 public class DataField {
 
-    public static final DataField DEFAULT = new DataField(0);
+    public static final DataField DEFAULT = new DataField(0, 8);
 
     private final int size;
     private long[] data;
+    private final int bits;
 
-    public DataField(int size) {
-        this(new long[size], size);
+    private transient ArrayList<DataListener> listeners;
+
+    public DataField(int size, int bits) {
+        this(new long[size], size, bits);
     }
 
-    private DataField(long[] data, int size) {
+    private DataField(long[] data, int size, int bits) {
         this.size = size;
         this.data = data;
+        this.bits = bits;
     }
 
-    public DataField(DataField dataField, int newSize) {
-        this(Arrays.copyOf(dataField.data, newSize), newSize);
+    public DataField(DataField dataField, int newSize, int bits) {
+        this(Arrays.copyOf(dataField.data, newSize), newSize, bits);
     }
 
     public DataField(File file) throws IOException {
@@ -53,13 +58,18 @@ public class DataField {
             }
             size = pos;
         }
+        bits = 16;
     }
 
     public void setData(int addr, long value) {
         if (addr < size) {
             if (addr >= data.length)
                 data = Arrays.copyOf(data, size);
-            data[addr] = value;
+
+            if (data[addr] != value) {
+                data[addr] = value;
+                fireChanged(addr);
+            }
         }
     }
 
@@ -80,6 +90,38 @@ public class DataField {
         if (pos == data.length)
             return this;
         else
-            return new DataField(Arrays.copyOf(data, pos), size);
+            return new DataField(Arrays.copyOf(data, pos), size, bits);
+    }
+
+    public int getBits() {
+        return bits;
+    }
+
+    public void addListener(DataListener l) {
+        if (listeners == null)
+            listeners = new ArrayList<>();
+        listeners.add(l);
+    }
+
+    public void removeListener(DataListener l) {
+        if (listeners == null)
+            return;
+
+        listeners.remove(l);
+        if (listeners.isEmpty())
+            listeners = null;
+    }
+
+    public void fireChanged(int addr) {
+        if (listeners == null)
+            return;
+
+        for (DataListener l : listeners)
+            l.valueChanged(addr);
+    }
+
+
+    public interface DataListener {
+        void valueChanged(int addr);
     }
 }
diff --git a/src/main/java/de/neemann/digital/core/memory/RAMDualPort.java b/src/main/java/de/neemann/digital/core/memory/RAMDualPort.java
index 7707f6810..98fbf59ee 100644
--- a/src/main/java/de/neemann/digital/core/memory/RAMDualPort.java
+++ b/src/main/java/de/neemann/digital/core/memory/RAMDualPort.java
@@ -11,12 +11,13 @@ import de.neemann.digital.core.element.ElementTypeDescription;
 /**
  * @author hneemann
  */
-public class RAMDualPort extends Node implements Element {
+public class RAMDualPort extends Node implements Element, RAMInterface {
 
 
     public static final ElementTypeDescription DESCRIPTION = new ElementTypeDescription(RAMDualPort.class, "A", "D", "str", "c", "ld")
             .addAttribute(AttributeKey.Bits)
             .addAttribute(AttributeKey.AddrBits)
+            .addAttribute(AttributeKey.Label)
             .setShortName("RAM");
 
     private final DataField memory;
@@ -36,7 +37,7 @@ public class RAMDualPort extends Node implements Element {
         bits = attr.get(AttributeKey.Bits);
         output = createOutput();
         addrBits = attr.get(AttributeKey.AddrBits);
-        memory = new DataField(1 << addrBits);
+        memory = new DataField(1 << addrBits, bits);
     }
 
     protected ObservableValue createOutput() {
@@ -87,4 +88,8 @@ public class RAMDualPort extends Node implements Element {
         }
     }
 
+    @Override
+    public DataField getMemory() {
+        return memory;
+    }
 }
diff --git a/src/main/java/de/neemann/digital/core/memory/RAMInterface.java b/src/main/java/de/neemann/digital/core/memory/RAMInterface.java
new file mode 100644
index 000000000..a70193be4
--- /dev/null
+++ b/src/main/java/de/neemann/digital/core/memory/RAMInterface.java
@@ -0,0 +1,8 @@
+package de.neemann.digital.core.memory;
+
+/**
+ * @author hneemann
+ */
+public interface RAMInterface {
+    DataField getMemory();
+}
diff --git a/src/main/java/de/neemann/digital/core/memory/RAMSinglePort.java b/src/main/java/de/neemann/digital/core/memory/RAMSinglePort.java
index c03b155e2..c4650d51f 100644
--- a/src/main/java/de/neemann/digital/core/memory/RAMSinglePort.java
+++ b/src/main/java/de/neemann/digital/core/memory/RAMSinglePort.java
@@ -11,16 +11,22 @@ import de.neemann.digital.core.element.ElementTypeDescription;
  */
 public class RAMSinglePort extends RAMDualPort {
 
-
     public static final ElementTypeDescription DESCRIPTION = new ElementTypeDescription(RAMSinglePort.class, "A", "str", "c", "ld")
             .addAttribute(AttributeKey.Bits)
             .addAttribute(AttributeKey.AddrBits)
+            .addAttribute(AttributeKey.Label)
             .setShortName("RAM");
 
     public RAMSinglePort(ElementAttributes attr) {
         super(attr);
     }
 
+    /**
+     * If a port is bidirectional an additional input comes with <code>setInputs</code>.
+     * Using this input you can read back the output port.
+     *
+     * @return outputs
+     */
     @Override
     protected ObservableValue createOutput() {
         return super.createOutput().setBidirectional(true);
@@ -32,7 +38,7 @@ public class RAMSinglePort extends RAMDualPort {
         strIn = inputs[1].checkBits(1, this).addObserver(this);
         clkIn = inputs[2].checkBits(1, this).addObserver(this);
         ldIn = inputs[3].checkBits(1, this).addObserver(this);
-        dataIn = inputs[4].checkBits(bits, this).addObserver(this);
+        dataIn = inputs[4].checkBits(bits, this).addObserver(this); // additional input to read the port
     }
 
 }
diff --git a/src/main/java/de/neemann/digital/core/memory/ROM.java b/src/main/java/de/neemann/digital/core/memory/ROM.java
index 55885aa99..cd35dbb91 100644
--- a/src/main/java/de/neemann/digital/core/memory/ROM.java
+++ b/src/main/java/de/neemann/digital/core/memory/ROM.java
@@ -17,6 +17,7 @@ public class ROM extends Node implements Element {
     public static final ElementTypeDescription DESCRIPTION = new ElementTypeDescription(ROM.class, "A", "sel")
             .addAttribute(AttributeKey.Bits)
             .addAttribute(AttributeKey.AddrBits)
+            .addAttribute(AttributeKey.Label)
             .addAttribute(AttributeKey.Data);
 
     private final DataField data;
diff --git a/src/main/java/de/neemann/digital/draw/elements/VisualElement.java b/src/main/java/de/neemann/digital/draw/elements/VisualElement.java
index 69d2d7564..1ccf526f8 100644
--- a/src/main/java/de/neemann/digital/draw/elements/VisualElement.java
+++ b/src/main/java/de/neemann/digital/draw/elements/VisualElement.java
@@ -3,6 +3,7 @@ package de.neemann.digital.draw.elements;
 import de.neemann.digital.core.Observer;
 import de.neemann.digital.core.element.AttributeKey;
 import de.neemann.digital.core.element.AttributeListener;
+import de.neemann.digital.core.element.Element;
 import de.neemann.digital.core.element.ElementAttributes;
 import de.neemann.digital.draw.graphics.*;
 import de.neemann.digital.draw.shapes.Drawable;
@@ -27,6 +28,7 @@ public class VisualElement implements Drawable, Moveable, AttributeListener {
     private transient IOState ioState;
     private transient Interactor interactor;
     private transient boolean highLight = false;
+    private transient Element element;
     private Vector pos;
     private int rotate;
 
@@ -182,7 +184,7 @@ public class VisualElement implements Drawable, Moveable, AttributeListener {
 
     public void clicked(CircuitComponent cc, Point pos) {
         if (interactor != null)
-            interactor.clicked(cc, pos, ioState);
+            interactor.clicked(cc, pos, ioState, element);
     }
 
     @Override
@@ -203,4 +205,12 @@ public class VisualElement implements Drawable, Moveable, AttributeListener {
         else
             return elementName;
     }
+
+    public void setElement(Element element) {
+        this.element = element;
+    }
+
+    public Element getElement() {
+        return element;
+    }
 }
\ No newline at end of file
diff --git a/src/main/java/de/neemann/digital/draw/model/ModelBuilder.java b/src/main/java/de/neemann/digital/draw/model/ModelBuilder.java
index e38876139..66453251a 100644
--- a/src/main/java/de/neemann/digital/draw/model/ModelBuilder.java
+++ b/src/main/java/de/neemann/digital/draw/model/ModelBuilder.java
@@ -16,7 +16,6 @@ import java.util.ArrayList;
 public class ModelBuilder {
 
     private final Circuit circuit;
-    private boolean bindWiresToGui = true;
     private boolean disableClock = false;
     private boolean enableTrace = false;
     private ModelDescription modelDescription;
@@ -25,11 +24,6 @@ public class ModelBuilder {
         this.circuit = circuit;
     }
 
-    public ModelBuilder setBindWiresToGui(boolean bindWiresToGui) {
-        this.bindWiresToGui = bindWiresToGui;
-        return this;
-    }
-
     public ModelBuilder setDisableClock(boolean disableClock) {
         this.disableClock = disableClock;
         return this;
@@ -42,7 +36,7 @@ public class ModelBuilder {
 
     public Model build(ElementLibrary library) throws PinException, NodeException {
         modelDescription = new ModelDescription(circuit, library);
-        Model model = modelDescription.createModel(bindWiresToGui);
+        Model model = modelDescription.createModel();
 
         if (enableTrace) {
 
diff --git a/src/main/java/de/neemann/digital/draw/model/ModelDescription.java b/src/main/java/de/neemann/digital/draw/model/ModelDescription.java
index f05a3c324..b1d9db71f 100644
--- a/src/main/java/de/neemann/digital/draw/model/ModelDescription.java
+++ b/src/main/java/de/neemann/digital/draw/model/ModelDescription.java
@@ -49,10 +49,11 @@ public class ModelDescription implements Iterable<ModelEntry> {
         else
             ioMap = null;
 
-        for (VisualElement vp : circuit.getElements()) {
-            Pins pins = vp.getPins();
-            ElementTypeDescription elementType = library.getElementType(vp.getElementName());
-            Element element = elementType.createElement(vp.getElementAttributes());
+        for (VisualElement ve : circuit.getElements()) {
+            Pins pins = ve.getPins();
+            ElementTypeDescription elementType = library.getElementType(ve.getElementName());
+            Element element = elementType.createElement(ve.getElementAttributes());
+            ve.setElement(element);
             pins.bindOutputsToOutputPins(element.getOutputs());
 
 
@@ -60,7 +61,7 @@ public class ModelDescription implements Iterable<ModelEntry> {
             boolean isNotAIO = true;
             if (readAsCustom) {
                 if (elementType == In.DESCRIPTION || elementType == Out.DESCRIPTION) {
-                    String label = vp.getElementAttributes().get(AttributeKey.Label);
+                    String label = ve.getElementAttributes().get(AttributeKey.Label);
                     if (label == null || label.length() == 0)
                         throw new PinException(Lang.get("err_pinWithoutName"));
                     if (pins.size() != 1)
@@ -72,7 +73,7 @@ public class ModelDescription implements Iterable<ModelEntry> {
             }
 
             if (isNotAIO)
-                entries.add(new ModelEntry(element, pins, vp, elementType.getInputNames(vp.getElementAttributes())));
+                entries.add(new ModelEntry(element, pins, ve, elementType.getInputNames(ve.getElementAttributes())));
 
             for (Pin p : pins)
                 netList.add(p);
@@ -129,14 +130,13 @@ public class ModelDescription implements Iterable<ModelEntry> {
     /**
      * Creates the model
      *
-     * @param bindWiresToValues
      * @return the model
      * @throws PinException
      * @throws NodeException
      */
-    public Model createModel(boolean bindWiresToValues) throws PinException, NodeException {
+    public Model createModel() throws PinException, NodeException {
         for (Net n : netList)
-            n.interconnect(bindWiresToValues);
+            n.interconnect();
 
         Model m = new Model();
 
diff --git a/src/main/java/de/neemann/digital/draw/model/Net.java b/src/main/java/de/neemann/digital/draw/model/Net.java
index f23f73f47..c6d11ec2c 100644
--- a/src/main/java/de/neemann/digital/draw/model/Net.java
+++ b/src/main/java/de/neemann/digital/draw/model/Net.java
@@ -71,7 +71,7 @@ public class Net {
         pins.addAll(p);
     }
 
-    public void interconnect(boolean bindWiresToValues) throws PinException {
+    public void interconnect() throws PinException {
         ArrayList<Pin> inputs = new ArrayList<>();
         ArrayList<Pin> outputs = new ArrayList<>();
         for (Pin p : pins) {
@@ -100,7 +100,7 @@ public class Net {
         for (Pin o : outputs)  // set also the reader for bidirectional pins
             o.setReaderValue(value);
 
-        if (bindWiresToValues && wires != null)
+        if (wires != null)
             for (Wire w : wires)
                 w.setValue(value);
     }
diff --git a/src/main/java/de/neemann/digital/draw/shapes/ClockShape.java b/src/main/java/de/neemann/digital/draw/shapes/ClockShape.java
index 85bedf379..3ac323710 100644
--- a/src/main/java/de/neemann/digital/draw/shapes/ClockShape.java
+++ b/src/main/java/de/neemann/digital/draw/shapes/ClockShape.java
@@ -2,6 +2,7 @@ package de.neemann.digital.draw.shapes;
 
 import de.neemann.digital.core.ObservableValue;
 import de.neemann.digital.core.Observer;
+import de.neemann.digital.core.element.Element;
 import de.neemann.digital.draw.elements.IOState;
 import de.neemann.digital.draw.elements.Pin;
 import de.neemann.digital.draw.elements.Pins;
@@ -34,7 +35,7 @@ public class ClockShape implements Shape {
         ioState.getOutput(0).addObserver(guiObserver); // necessary to replot wires also if component itself does not depend on state
         return new Interactor() {
             @Override
-            public void clicked(CircuitComponent cc, Point pos, IOState ioState) {
+            public void clicked(CircuitComponent cc, Point pos, IOState ioState, Element element) {
                 ObservableValue value = ioState.getOutput(0);
                 if (value.getBits() == 1) {
                     value.setValue(1 - value.getValue());
diff --git a/src/main/java/de/neemann/digital/draw/shapes/InputShape.java b/src/main/java/de/neemann/digital/draw/shapes/InputShape.java
index ee3bfe154..d67dd2201 100644
--- a/src/main/java/de/neemann/digital/draw/shapes/InputShape.java
+++ b/src/main/java/de/neemann/digital/draw/shapes/InputShape.java
@@ -2,6 +2,7 @@ package de.neemann.digital.draw.shapes;
 
 import de.neemann.digital.core.ObservableValue;
 import de.neemann.digital.core.Observer;
+import de.neemann.digital.core.element.Element;
 import de.neemann.digital.draw.elements.IOState;
 import de.neemann.digital.draw.elements.Pin;
 import de.neemann.digital.draw.elements.Pins;
@@ -38,7 +39,7 @@ public class InputShape implements Shape {
         ioState.getOutput(0).addObserver(guiObserver);
         return new Interactor() {
             @Override
-            public void clicked(CircuitComponent cc, Point pos, IOState ioState) {
+            public void clicked(CircuitComponent cc, Point pos, IOState ioState, Element element) {
                 ObservableValue value = ioState.getOutput(0);
                 if (value.getBits() == 1) {
                     value.setValue(1 - value.getValue());
diff --git a/src/main/java/de/neemann/digital/draw/shapes/Interactor.java b/src/main/java/de/neemann/digital/draw/shapes/Interactor.java
index 671526fb4..f3894fa53 100644
--- a/src/main/java/de/neemann/digital/draw/shapes/Interactor.java
+++ b/src/main/java/de/neemann/digital/draw/shapes/Interactor.java
@@ -1,5 +1,6 @@
 package de.neemann.digital.draw.shapes;
 
+import de.neemann.digital.core.element.Element;
 import de.neemann.digital.draw.elements.IOState;
 import de.neemann.digital.gui.components.CircuitComponent;
 
@@ -22,5 +23,5 @@ public interface Interactor {
      * @param pos     the popuplocation on screen
      * @param ioState the state of the element
      */
-    void clicked(CircuitComponent cc, Point pos, IOState ioState);
+    void clicked(CircuitComponent cc, Point pos, IOState ioState, Element element);
 }
diff --git a/src/main/java/de/neemann/digital/draw/shapes/RAMShape.java b/src/main/java/de/neemann/digital/draw/shapes/RAMShape.java
new file mode 100644
index 000000000..fd034ac2a
--- /dev/null
+++ b/src/main/java/de/neemann/digital/draw/shapes/RAMShape.java
@@ -0,0 +1,33 @@
+package de.neemann.digital.draw.shapes;
+
+import de.neemann.digital.core.Observer;
+import de.neemann.digital.core.element.Element;
+import de.neemann.digital.core.memory.DataField;
+import de.neemann.digital.core.memory.RAMInterface;
+import de.neemann.digital.draw.elements.IOState;
+import de.neemann.digital.gui.components.CircuitComponent;
+import de.neemann.digital.gui.components.DataEditor;
+
+import java.awt.*;
+
+/**
+ * @author hneemann
+ */
+public class RAMShape extends GenericShape {
+    public RAMShape(String name, String[] inputs, OutputPinInfo[] outputs, String label) {
+        super(name, inputs, outputs, label, true);
+    }
+
+    @Override
+    public Interactor applyStateMonitor(IOState ioState, Observer guiObserver) {
+        return new Interactor() {
+            @Override
+            public void clicked(CircuitComponent cc, Point pos, IOState ioState, Element element) {
+                if (element instanceof RAMInterface) {
+                    DataField dataField = ((RAMInterface) element).getMemory();
+                    new DataEditor(cc, dataField).showDialog();
+                }
+            }
+        };
+    }
+}
diff --git a/src/main/java/de/neemann/digital/draw/shapes/ShapeFactory.java b/src/main/java/de/neemann/digital/draw/shapes/ShapeFactory.java
index 4288a796c..576d48374 100644
--- a/src/main/java/de/neemann/digital/draw/shapes/ShapeFactory.java
+++ b/src/main/java/de/neemann/digital/draw/shapes/ShapeFactory.java
@@ -12,6 +12,8 @@ import de.neemann.digital.core.element.ElementTypeDescription;
 import de.neemann.digital.core.io.Const;
 import de.neemann.digital.core.io.In;
 import de.neemann.digital.core.io.Out;
+import de.neemann.digital.core.memory.RAMDualPort;
+import de.neemann.digital.core.memory.RAMSinglePort;
 import de.neemann.digital.core.wiring.*;
 import de.neemann.digital.draw.library.ElementLibrary;
 import de.neemann.digital.lang.Lang;
@@ -49,6 +51,8 @@ public final class ShapeFactory {
         map.put(Sub.DESCRIPTION.getName(), attr -> new GenericShape("-", Sub.DESCRIPTION.getInputNames(attr), outputInfos(Sub.DESCRIPTION, attr), null, true));
         map.put(Mul.DESCRIPTION.getName(), attr -> new GenericShape("*", Mul.DESCRIPTION.getInputNames(attr), outputInfos(Mul.DESCRIPTION, attr), null, true));
 
+        map.put(RAMDualPort.DESCRIPTION.getName(), attr -> new RAMShape("RAM", RAMDualPort.DESCRIPTION.getInputNames(attr), outputInfos(RAMDualPort.DESCRIPTION, attr), attr.get(AttributeKey.Label)));
+        map.put(RAMSinglePort.DESCRIPTION.getName(), attr -> new RAMShape("RAM", RAMSinglePort.DESCRIPTION.getInputNames(attr), outputInfos(RAMSinglePort.DESCRIPTION, attr), attr.get(AttributeKey.Label)));
 
         map.put(In.DESCRIPTION.getName(), attr -> new InputShape(attr.get(AttributeKey.Label)));
         map.put(Const.DESCRIPTION.getName(), attr -> new ConstShape(attr.get(AttributeKey.Value)));
diff --git a/src/main/java/de/neemann/digital/gui/Main.java b/src/main/java/de/neemann/digital/gui/Main.java
index c2c7a6be5..25e7e5c61 100644
--- a/src/main/java/de/neemann/digital/gui/Main.java
+++ b/src/main/java/de/neemann/digital/gui/Main.java
@@ -56,7 +56,6 @@ public class Main extends JFrame implements ClosingWindowListener.ConfirmSave {
         super(Lang.get("digital"));
         setDefaultCloseOperation(DO_NOTHING_ON_CLOSE);
 
-
         Circuit cr = new Circuit();
         circuitComponent = new CircuitComponent(cr, library);
         String name = prefs.get("name", null);
@@ -195,7 +194,6 @@ public class Main extends JFrame implements ClosingWindowListener.ConfirmSave {
             public void actionPerformed(ActionEvent e) {
                 try {
                     Model model = new ModelBuilder(circuitComponent.getCircuit())
-                            .setBindWiresToGui(false)
                             .build(library);
 
                     SpeedTest speedTest = new SpeedTest(model);
@@ -255,7 +253,6 @@ public class Main extends JFrame implements ClosingWindowListener.ConfirmSave {
             circuitComponent.setModeAndReset(CircuitComponent.Mode.running);
 
             mb = new ModelBuilder(circuitComponent.getCircuit())
-                    .setBindWiresToGui(true)
                     .setDisableClock(!runClock)
                     .setEnableTrace(traceEnable.isSelected(), Main.this);
 
diff --git a/src/main/java/de/neemann/digital/gui/components/DataEditor.java b/src/main/java/de/neemann/digital/gui/components/DataEditor.java
index 61f99955f..310f643e6 100644
--- a/src/main/java/de/neemann/digital/gui/components/DataEditor.java
+++ b/src/main/java/de/neemann/digital/gui/components/DataEditor.java
@@ -6,11 +6,14 @@ import de.neemann.digital.core.memory.DataField;
 import de.neemann.digital.lang.Lang;
 
 import javax.swing.*;
+import javax.swing.event.TableModelEvent;
 import javax.swing.event.TableModelListener;
 import javax.swing.table.DefaultTableCellRenderer;
 import javax.swing.table.TableModel;
 import java.awt.*;
 import java.awt.event.ActionEvent;
+import java.awt.event.WindowAdapter;
+import java.awt.event.WindowEvent;
 import java.util.ArrayList;
 
 /**
@@ -20,26 +23,54 @@ public class DataEditor extends JDialog {
     private final DataField dataField;
     private boolean ok = false;
 
+    public DataEditor(JComponent parent, DataField dataField) {
+        this(parent, dataField, null);
+    }
+
     public DataEditor(JComponent parent, DataField dataField, ElementAttributes attr) {
-        super(SwingUtilities.windowForComponent(parent), Lang.get("key_data"), ModalityType.APPLICATION_MODAL);
+        super(SwingUtilities.windowForComponent(parent), Lang.get("key_data"), attr == null ? ModalityType.MODELESS : ModalityType.APPLICATION_MODAL);
+        setDefaultCloseOperation(DISPOSE_ON_CLOSE);
 
-        int bits = attr.getBits();
         int size;
-        if (attr.contains(AttributeKey.AddrBits))
-            size = 1 << attr.get(AttributeKey.AddrBits);
-        else
-            size = 1 << attr.get(AttributeKey.InputCount);
+        int bits;
+        boolean register;
+        if (attr != null) {
+            bits = attr.getBits();
+            if (attr.contains(AttributeKey.AddrBits))
+                size = 1 << attr.get(AttributeKey.AddrBits);
+            else
+                size = 1 << attr.get(AttributeKey.InputCount);
 
-        this.dataField = new DataField(dataField, size);
+            this.dataField = new DataField(dataField, size, bits);
+            register = false;
+        } else {
+            this.dataField = dataField;
+            size = this.dataField.size();
+            bits = this.dataField.getBits();
+            register = true;
+        }
 
         int cols = 16;
         if (size <= 16) cols = 1;
         else if (size <= 128) cols = 8;
 
-        JTable table = new JTable(new MyTableModel(this.dataField, cols));
+        MyTableModel dm = new MyTableModel(this.dataField, cols);
+        JTable table = new JTable(dm);
         table.setDefaultRenderer(MyLong.class, new MyLongRenderer(bits));
         getContentPane().add(new JScrollPane(table));
 
+        if (register) {
+            this.dataField.addListener(dm);
+
+            addWindowListener(new WindowAdapter() {
+                @Override
+                public void windowClosed(WindowEvent e) {
+                    DataEditor.this.dataField.removeListener(dm);
+                }
+            });
+        }
+
+
         JPanel buttons = new JPanel(new FlowLayout(FlowLayout.RIGHT));
         buttons.add(new JButton(new AbstractAction(Lang.get("ok")) {
             @Override
@@ -50,7 +81,10 @@ public class DataEditor extends JDialog {
         }));
         getContentPane().add(buttons, BorderLayout.SOUTH);
 
+        setPreferredSize(new Dimension((cols + 1) * 50, getPreferredSize().height));
+
         pack();
+
         setLocationRelativeTo(parent);
     }
 
@@ -63,7 +97,7 @@ public class DataEditor extends JDialog {
         return ok;
     }
 
-    private class MyTableModel implements TableModel {
+    private class MyTableModel implements TableModel, DataField.DataListener {
         private final DataField dataField;
         private final int cols;
         private final int rows;
@@ -118,6 +152,11 @@ public class DataEditor extends JDialog {
             dataField.setData(rowIndex * cols + (columnIndex - 1), ((MyLong) aValue).getValue());
         }
 
+        public void fireEvent(TableModelEvent e) {
+            for (TableModelListener l : listener)
+                l.tableChanged(e);
+        }
+
         @Override
         public void addTableModelListener(TableModelListener l) {
             listener.add(l);
@@ -127,6 +166,11 @@ public class DataEditor extends JDialog {
         public void removeTableModelListener(TableModelListener l) {
             listener.remove(l);
         }
+
+        @Override
+        public void valueChanged(int addr) {
+            fireEvent(new TableModelEvent(this, addr / cols));
+        }
     }
 
 
diff --git a/src/test/java/de/neemann/digital/core/memory/DataFieldTest.java b/src/test/java/de/neemann/digital/core/memory/DataFieldTest.java
index 87c87ddb0..f5851abbe 100644
--- a/src/test/java/de/neemann/digital/core/memory/DataFieldTest.java
+++ b/src/test/java/de/neemann/digital/core/memory/DataFieldTest.java
@@ -10,7 +10,7 @@ import java.io.StringReader;
 public class DataFieldTest extends TestCase {
 
     public void testGetMinimized() throws Exception {
-        DataField data = new DataField(100);
+        DataField data = new DataField(100, 8);
         data.setData(9, 1);
         data = data.getMinimized();
         assertEquals(1, data.getData(9));
@@ -19,7 +19,7 @@ public class DataFieldTest extends TestCase {
     }
 
     public void testGrow() throws Exception {
-        DataField data = new DataField(100);
+        DataField data = new DataField(100, 8);
         data.setData(9, 1);
         data = data.getMinimized();
         assertEquals(1, data.getData(9));
diff --git a/src/test/java/de/neemann/digital/core/memory/LUTTest.java b/src/test/java/de/neemann/digital/core/memory/LUTTest.java
index c3aa10f9b..e41ba78b9 100644
--- a/src/test/java/de/neemann/digital/core/memory/LUTTest.java
+++ b/src/test/java/de/neemann/digital/core/memory/LUTTest.java
@@ -18,7 +18,7 @@ public class LUTTest extends TestCase {
         ObservableValue c = new ObservableValue("c", 1);
 
         Model model = new Model();
-        DataField data = new DataField(8);
+        DataField data = new DataField(8, 8);
         data.setData(3, 1);
         data.setData(7, 1);
         LookUpTable out = model.add(new LookUpTable(
diff --git a/src/test/java/de/neemann/digital/core/memory/ROMTest.java b/src/test/java/de/neemann/digital/core/memory/ROMTest.java
index 511dbcd51..51d3fdc91 100644
--- a/src/test/java/de/neemann/digital/core/memory/ROMTest.java
+++ b/src/test/java/de/neemann/digital/core/memory/ROMTest.java
@@ -18,7 +18,7 @@ public class ROMTest extends TestCase {
         ObservableValue sel = new ObservableValue("sel", 1);
 
         Model model = new Model();
-        DataField data = new DataField(8);
+        DataField data = new DataField(8, 8);
         data.setData(3, 17);
         data.setData(7, 200);
         ROM out = model.add(new ROM(