diff --git a/mpmaster/src/main/java/com/xypower/mpmaster/MainActivity.java b/mpmaster/src/main/java/com/xypower/mpmaster/MainActivity.java
index d5077703..239fac0e 100644
--- a/mpmaster/src/main/java/com/xypower/mpmaster/MainActivity.java
+++ b/mpmaster/src/main/java/com/xypower/mpmaster/MainActivity.java
@@ -107,6 +107,8 @@ public class MainActivity extends AppCompatActivity {
             }
         });
 
+        Switch sw = (Switch)findViewById(R.id.btn485ReadMode);
+        sw.setChecked(true);
         findViewById(R.id.btn485ReadMode).setOnClickListener(new View.OnClickListener() {
             @Override
             public void onClick(View view) {