diff --git a/commandedit.cpp b/commandedit.cpp
new file mode 100644
--- /dev/null
+++ b/commandedit.cpp
@@ -0,0 +1,102 @@
+/*
+  Copyright © 2015 Hasan Yavuz Özderya
+
+  This file is part of serialplot.
+
+  serialplot is free software: you can redistribute it and/or modify
+  it under the terms of the GNU General Public License as published by
+  the Free Software Foundation, either version 3 of the License, or
+  (at your option) any later version.
+
+  serialplot is distributed in the hope that it will be useful,
+  but WITHOUT ANY WARRANTY; without even the implied warranty of
+  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+  GNU General Public License for more details.
+
+  You should have received a copy of the GNU General Public License
+  along with serialplot.  If not, see <http://www.gnu.org/licenses/>.
+*/
+
+#include <QKeyEvent>
+
+#include "commandedit.h"
+
+class HexCommandValidator : public QRegExpValidator
+{
+public:
+    explicit HexCommandValidator(QObject* parent = 0);
+    QValidator::State validate(QString & input, int & pos) const;
+};
+
+HexCommandValidator::HexCommandValidator(QObject* parent) :
+    QRegExpValidator(parent)
+{
+    QRegExp regExp("^(?:(?:[0-9A-F]{2}[ ])+(?:[0-9A-F]{2}))|(?:[0-9A-F]{2})$");
+    setRegExp(regExp);
+}
+
+QValidator::State HexCommandValidator::validate(QString & input, int & pos) const
+{
+    input = input.toUpper();
+
+    // don't let pos to be altered at this stage
+    int orgPos = pos;
+    auto r = QRegExpValidator::validate(input, pos);
+    pos = orgPos;
+
+    // try fixing up spaces
+    if (r != QValidator::Acceptable)
+    {
+        input = input.replace(" ", "");
+        input.replace(QRegExp("([0-9A-F]{2}(?!$))"), "\\1 ");
+        if (pos == input.size()-1) pos = input.size();
+        r = QRegExpValidator::validate(input, pos);
+    }
+
+    return r;
+}
+
+CommandEdit::CommandEdit(QWidget *parent) :
+    QLineEdit(parent)
+{
+    hexValidator = new HexCommandValidator(this);
+    ascii_mode = true;
+}
+
+CommandEdit::~CommandEdit()
+{
+    delete hexValidator;
+}
+
+void CommandEdit::setMode(bool ascii)
+{
+    ascii_mode = ascii;
+    if (ascii)
+    {
+        setValidator(0);
+    }
+    else
+    {
+        setValidator(hexValidator);
+    }
+}
+
+void CommandEdit::keyPressEvent(QKeyEvent * event)
+{
+    if (ascii_mode)
+    {
+        QLineEdit::keyPressEvent(event);
+        return;
+    }
+
+    if (event->key() == Qt::Key_Backspace && !hasSelectedText())
+    {
+        int cursor = cursorPosition();
+        if (cursor != 0 && text()[cursor-1] == ' ')
+        {
+            setCursorPosition(cursor-1);
+        }
+    }
+
+    QLineEdit::keyPressEvent(event);
+}