diff --git a/ModbusMaster/MasterForm.cs b/ModbusMaster/MasterForm.cs
index 40489f8..3e8ba39 100644
--- a/ModbusMaster/MasterForm.cs
+++ b/ModbusMaster/MasterForm.cs
@@ -272,6 +272,10 @@ private void cbPoll_CheckStateChanged(object sender, EventArgs e)
 
         private void pollTimer_Tick(object sender, EventArgs e)
         {
+            // disconnected state, skip
+            if (groupBoxFunctions.Enabled == false)
+                return;
+
             if (_lastReadCommand != 0)
                 ExecuteReadCommand(_lastReadCommand);
         }