diff --git a/usbd_cdc_if.c b/usbd_cdc_if.c
--- a/usbd_cdc_if.c
+++ b/usbd_cdc_if.c
@@ -290,10 +290,13 @@ uint8_t CDC_Transmit_FS(uint8_t* Buf, ui
     /* USER CODE BEGIN 8 */
     uint16_t i;
 
+
+    // Zero out user TX buffer (EMZ FIXME: why bother?)
     for (i=0; i < sizeof(UserTxBufferFS); i++) {
 	UserTxBufferFS[i] = 0;
     }
 
+    // Copy input buff to user TX buffer
     for (i=0; i < Len; i++) {
 	UserTxBufferFS[i] = Buf[i];
     }