diff -r f71f6c0af3cd -r 897330ee6e9d src/def_hp34970_fp.h
--- a/src/def_hp34970_fp.h	Thu Sep 09 21:59:53 2021 +0200
+++ b/src/def_hp34970_fp.h	Sun Oct 03 22:58:49 2021 +0200
@@ -35,10 +35,14 @@
 #define KP_C4 PB_0
 
 #if defined(HAVE_PC)
-//#include <USBSerial.h>
-//USBSerial pc;
+
+#include <USBSerial.h>
+#if 1
+USBSerial pc(false);  // PA_11 USB_DM, PA_12 USB_DP (with 1.5k pull-up)
+#else
 BufferedSerial pc(PC_10_ALT0, PC_11_ALT0, 115200); // UART_4
-//BufferedSerial pc(PC_10, PC_11, 115200); // UART_4
 #endif
 
 #endif
+
+#endif