Come ti ho detto ...
gpb01:
Controlla sempre bene la porta veramente usata ... la Leonardo ha il vizio, ad ogni reset, di cambiare COMx:
... del resto ... è anche spiegato al link che ti avevo dato ... QUI !
Serial re-enumeration on reset.
Since the boards do not have a dedicated chip to handle serial communication, it means that the serial port is virtual -- it's a software routine, both on your operating system, and on the board itself. Just as your computer creates an instance of the serial port driver when you plug in any Arduino, the Leonardo/Micro creates a serial instance whenever it runs its bootloader. The board is an instance of USB's Connected Device Class (CDC) driver.
This means that every time you reset the board, the USB serial connection will be broken and re-established. The board will disappear from the list of serial ports, and the list will re-enumerate. Any program that has an open serial connection to the Leonardo will lose its connection. This is in contrast to the Arduino Uno, with which you can reset the main processor (the ATmega328P) without closing the USB connection (which is maintained by the secondary ATmega8U2 or ATmega16U2 processor). This difference has implications for driver installation, uploading, and communication; these are discussed below.
Uploading Code to the Leonardo and Micro
In general, you upload code to the Leonardo or Micro as you would with the Uno or other Arduino boards. Click the upload button in the Arduino IDE and your sketch will be automatically uploaded onto the board and then started. This works more or less the same way as with the Uno: the Arduino software initiates a reset of the board, launching the bootloader - which is responsible for receiving, storing, and starting the new sketch.
However, because the serial port is virtual, it disappears when the board resets, the Arduino software uses a different strategy for timing the upload than with the Uno and other boards. In particular, after initiating the auto-reset of the Leonardo or Micro (using the serial port selected in the Tools > Serial Port menu), the Arduino software waits for a new virtual (CDC) serial / COM port to appear - one that it assumes represents the bootloader. It then performs the upload on this newly-appeared port.
These differences affect the way you use the physical reset button to perform an upload if the auto-reset isn't working. Press and hold the reset button on the Leonardo or Micro, then hit the upload button in the Arduino software. Only release the reset button after you see the message "Uploading..." appear in the software's status bar. When you do so, the bootloader will start, creating a new virtual (CDC) serial port on the computer. The software will see that port appear and perform the upload using it. Again, this is only necessary if the normal upload process (i.e. just pressing the uploading button) doesn't work. (Note that the auto-reset is initiated when the computer opens the serial port at 1200 baud and then closes it; this won't work if something interferes with the board's USB communication - e.g. disabling interrupts.)
Guglielmo