diff --git a/firmware/src_simtrace/simtrace_iso7816.c b/firmware/src_simtrace/simtrace_iso7816.c
index 5325bba4..0c4a0963 100644
--- a/firmware/src_simtrace/simtrace_iso7816.c
+++ b/firmware/src_simtrace/simtrace_iso7816.c
@@ -72,12 +72,14 @@ void ISR_PhoneRST( const Pin *pPin)
     PIO_DisableIt( &pinPhoneRST ) ;
 }
 
+extern void usart_irq_rx(uint8_t num);
 /*
  *  char_stat is zero if no error occured.
  *  Otherwise it is filled with the content of the status register.
  */
 void USART1_IrqHandler( void )
 {
+#if 0
     uint32_t stat;
     char_stat = 0;
     // Rcv buf full
@@ -107,6 +109,9 @@ void USART1_IrqHandler( void )
 
         char_stat = stat;
     }
+#else
+    usart_irq_rx(0);
+#endif
 }
 
 /*  FIDI update functions   */