diff --git a/src/main/scala/backBoard/shin/MstSlvSwitch.scala b/src/main/scala/backBoard/shin/MstSlvSwitch.scala
index 46ea84f..b861c1a 100644
--- a/src/main/scala/backBoard/shin/MstSlvSwitch.scala
+++ b/src/main/scala/backBoard/shin/MstSlvSwitch.scala
@@ -592,7 +592,7 @@ trait MstSlvSwitchDataPath{ this: MstSlvSwitchBase =>
 }
 
 trait MstSlvSwitchB8B4{ this: MstSlvSwitchBase =>
-  val isUsing8b10b = interface.io.cReg.b8b4Sel.extract(0)
+  val isUsing8b10b = ~interface.io.cReg.b8b4Sel.extract(0)
 
   when( isUsing8b10b ){
     b8b10DownEncoder.io <> downCDROut.io.encode