diff --git a/armsrc/appmain.c b/armsrc/appmain.c
index 186f5a654..d4893359a 100644
--- a/armsrc/appmain.c
+++ b/armsrc/appmain.c
@@ -1123,7 +1123,13 @@ static void PacketReceived(PacketCommandNG *packet) {
             break;
         }
         case CMD_LF_EM4X50_SIM: {
-            em4x50_sim();
+            //-----------------------------------------------------------------------------
+            // Note: we call FpgaDownloadAndGo(FPGA_BITSTREAM_LF) here although FPGA is not
+            // involved in dealing with emulator memory. But if it is called later, it might
+            // destroy the Emulator Memory.
+            //-----------------------------------------------------------------------------
+            FpgaDownloadAndGo(FPGA_BITSTREAM_LF);
+            em4x50_sim((uint8_t *)packet->data.asBytes);
             break;
         }
         case CMD_LF_EM4X50_READER: {
diff --git a/armsrc/em4x50.h b/armsrc/em4x50.h
index 33c18e794..12f0a64d8 100644
--- a/armsrc/em4x50.h
+++ b/armsrc/em4x50.h
@@ -24,7 +24,7 @@ void em4x50_writepwd(em4x50_data_t *etd);
 void em4x50_read(em4x50_data_t *etd);
 void em4x50_brute(em4x50_data_t *etd);
 void em4x50_login(uint32_t *password);
-void em4x50_sim(void);
+void em4x50_sim(uint8_t *filename);
 void em4x50_reader(void);
 void em4x50_chk(uint8_t *filename);