diff --git a/misc/config_tools/schema/VMtypes.xsd b/misc/config_tools/schema/VMtypes.xsd
index 24c71874e..77d6c87f7 100644
--- a/misc/config_tools/schema/VMtypes.xsd
+++ b/misc/config_tools/schema/VMtypes.xsd
@@ -215,8 +215,8 @@ The size is a subset of the VM's total memory size specified on the Basic tab.</
         <xs:documentation>Virtual UART port</xs:documentation>
       </xs:annotation>
     </xs:element>
-    <xs:element name="io_port" type="HexFormat" default="0x3F">
-      <xs:annotation acrn:title="Virtual I/O address" acrn:widget-options="'placeholder':'An address in hexadecimal, e.g. 0x4000'">
+    <xs:element name="io_port" type="HexFormat">
+      <xs:annotation acrn:title="Virtual I/O address" acrn:defaults="[hex(i) for i in range(0x9200, 0x9280, 8)]" acrn:unique-among="//vuart_connection/endpoint[vm_name=$parent/vm_name]/io_port/text()">
         <xs:documentation>Specify the COM base for each legacy virtual UART.</xs:documentation>
       </xs:annotation>
     </xs:element>