diff --git a/doc/revpicheckclient.html b/doc/revpicheckclient.html
index 7b5ca6f..2069514 100644
--- a/doc/revpicheckclient.html
+++ b/doc/revpicheckclient.html
@@ -82,6 +82,9 @@ Methods</h3>
 <td><a style="color:#0000FF" href="#RevPiCheckClient.hideallwindows">hideallwindows</a></td>
 <td>Versteckt alle Fenster.</td>
 </tr><tr>
+<td><a style="color:#0000FF" href="#RevPiCheckClient.maxint">maxint</a></td>
+<td>Errechnet maximalen int() Wert f&#252;r Bytes max 22.</td>
+</tr><tr>
 <td><a style="color:#0000FF" href="#RevPiCheckClient.readvalues">readvalues</a></td>
 <td>Ruft nur Input Werte von RevPi ab und aktualisiert Fenster.</td>
 </tr><tr>
@@ -236,7 +239,23 @@ RevPiCheckClient.hideallwindows</h3>
 <b>hideallwindows</b>(<i></i>)
 <p>
 Versteckt alle Fenster.
-</p><a NAME="RevPiCheckClient.readvalues" ID="RevPiCheckClient.readvalues"></a>
+</p><a NAME="RevPiCheckClient.maxint" ID="RevPiCheckClient.maxint"></a>
+<h3 style="background-color:#FFFFFF;color:#FF0000">
+RevPiCheckClient.maxint</h3>
+<b>maxint</b>(<i>bytelen</i>)
+<p>
+Errechnet maximalen int() Wert f&#252;r Bytes max 22.
+</p><dl>
+<dt><i>bytelen</i></dt>
+<dd>
+Anzahl Bytes
+</dd>
+</dl><dl>
+<dt>Returns:</dt>
+<dd>
+int() max oder 0 bei &#220;berschreitung
+</dd>
+</dl><a NAME="RevPiCheckClient.readvalues" ID="RevPiCheckClient.readvalues"></a>
 <h3 style="background-color:#FFFFFF;color:#FF0000">
 RevPiCheckClient.readvalues</h3>
 <b>readvalues</b>(<i></i>)
diff --git a/revpipycontrol.api b/revpipycontrol.api
index 0fcb54c..4c807c3 100644
--- a/revpipycontrol.api
+++ b/revpipycontrol.api
@@ -11,6 +11,7 @@ revpicheckclient.RevPiCheckClient._onfrmconf?5(canvas)
 revpicheckclient.RevPiCheckClient._warnwrite?5()
 revpicheckclient.RevPiCheckClient._workvalues?5(io_dicts=None, writeout=False)
 revpicheckclient.RevPiCheckClient.hideallwindows?4()
+revpicheckclient.RevPiCheckClient.maxint?4(bytelen)
 revpicheckclient.RevPiCheckClient.readvalues?4()
 revpicheckclient.RevPiCheckClient.refreshvalues?4()
 revpicheckclient.RevPiCheckClient.tmr_workvalues?4()
diff --git a/revpipycontrol/revpicheckclient.py b/revpipycontrol/revpicheckclient.py
index 9226f2e..1b25490 100644
--- a/revpipycontrol/revpicheckclient.py
+++ b/revpipycontrol/revpicheckclient.py
@@ -96,7 +96,7 @@ class RevPiCheckClient(tkinter.Frame):
         try:
             newvalue = io[5].get()
             # Wertebereich prüfen
-            if newvalue < 0 or newvalue > 256 ** io[1] - 1:
+            if newvalue < 0 or newvalue > self.maxint(io[1]):
                 raise ValueError("too big")
 
             self.__chval(device, io)
@@ -177,7 +177,7 @@ class RevPiCheckClient(tkinter.Frame):
                 check.grid(column=1, row=rowcount)
             else:
                 var = tkinter.IntVar()
-                txt = tkinter.Spinbox(s_frame, to=256 ** io[1] - 1)
+                txt = tkinter.Spinbox(s_frame, to=self.maxint(io[1]))
                 txt.bind(
                     "<Key>",
                     lambda event, tkvar=var: self.__saveoldvalue(event, tkvar)
@@ -189,7 +189,8 @@ class RevPiCheckClient(tkinter.Frame):
                 )
                 txt["command"] = \
                     lambda device=device, io=io: self.__chval(device, io)
-                txt["state"] = "disabled" if iotype == "inp" else "normal"
+                txt["state"] = "disabled" if iotype == "inp" or \
+                    self.maxint(io[1]) == 0 else "normal"
                 txt["width"] = 5
                 txt["textvariable"] = var
                 txt.grid(column=1, row=rowcount)
@@ -363,6 +364,12 @@ class RevPiCheckClient(tkinter.Frame):
         for win in self.dict_wins:
             self.dict_wins[win].withdraw()
 
+    def maxint(self, bytelen):
+        u"""Errechnet maximalen int() Wert für Bytes max 22.
+        @param bytelen Anzahl Bytes
+        @return int() max oder 0 bei Überschreitung"""
+        return 0 if bytelen > 22 else 256 ** bytelen - 1
+
     def readvalues(self):
         u"""Ruft nur Input Werte von RevPi ab und aktualisiert Fenster."""
         if not self.autorw.get():