diff --git a/Cart_Reader/GBM.ino b/Cart_Reader/GBM.ino
index f376706..0790539 100644
--- a/Cart_Reader/GBM.ino
+++ b/Cart_Reader/GBM.ino
@@ -403,13 +403,13 @@ void send_GBM(byte myCommand) {
       break;
 
     case 0x04:
-      //CMD_04h -> Map entire flashrom (MBC4 mode)
+      //CMD_04h -> Disable mapping; makes the entire flash and SRAM accessible
       writeByte_GBM(0x0120, 0x04);
       writeByte_GBM(0x013F, 0xA5);
       break;
 
     case 0x05:
-      //CMD_05h -> Map menu (MBC5 mode)
+      //CMD_05h -> Enable mapping; re-enables the mapping that was previously selected by 0xCn
       writeByte_GBM(0x0120, 0x05);
       writeByte_GBM(0x013F, 0xA5);
       break;
@@ -479,8 +479,14 @@ void switchGame_GBM(byte myData) {
   // Enable ports 0x0120 (F2)
   send_GBM(0x09);
 
+  // Enable mapping. Mapping must be enabled before the C0 cmd, otherwise switching has no effect.
+  send_GBM(0x05);
+
   //CMD_C0h -> map selected game without reset
-  writeByte_GBM(0x0120, 0xC0 & myData);
+  //           C0 is the menu or a single 1MB sized game
+  //           C1 is the first game entry
+  //           C2 is the second game entry...
+  writeByte_GBM(0x0120, 0xC0 | myData);
   writeByte_GBM(0x013F, 0xA5);
 }
 
@@ -918,4 +924,4 @@ void writeMapping_GBM() {
 
 //******************************************
 // End of File
-//******************************************
\ No newline at end of file
+//******************************************