Atmega16U2/Atmega8U2 DFU articles refactor [HC-1599]

content/Hardware Support/Generic/Flash-the-USB-to-serial-firmware-for-UNO-R3-or-earlier-and-Mega-boards.md

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+---
+title: "Flash the USB-to-serial firmware for UNO (R3 or earlier) and Mega boards"
+id: 4408887452434
+---
+
+The following boards use either an Atmega16U2 or Atmega8U2 chip as a USB-to-serial converter:
+
+* Arduino UNO (R3 or earlier, including SMD variants)
+* Arduino Mega (Rev3 or earlier)
+* Arduino Mega2560 Rev3
+* Arduino MegaADK Rev3
+
+If the Arduino firmware for these chips is missing or has been corrupted, it will no longer be possible to program the board over USB. However, Atmega16U2 or Atmega8U2 chips support a DFU (Device Firmware Upgrade) protocol that can be used to flash the Arduino firmware via USB, to restore USB-to-serial functionality.
+
+You may want to try this procedure if:
+
+* Your board is not being detected properly, and you already tried [the standard troubleshooting steps](https://support.arduino.cc/hc/en-us/articles/4412955149586-If-your-board-is-not-detected-by-Arduino-IDE).
+* You have replaced the Atmega16U2 or Atmega8U2 with a new chip that is missing the Arduino firmware.
+
+---
+
+## 1. Get the firmware
+
+The firmware is included in the **Arduino AVR Boards** package. When it's installed, you can find the firmware inside the [Arduino15 folder](https://support.arduino.cc/hc/en-us/articles/360018448279-Where-can-I-find-the-Arduino15-folder-):
+
+* Windows: `%USERPROFILE%\AppData\Local\Arduino15\packages\arduino\hardware\avr\1.8.6\firmwares\atmegaxxu2\arduino-usbserial`
+* macoS: `~/Library/Arduino15/packages/arduino/hardware/avr/1.8.6/firmwares/atmegaxxu2/arduino-usbserial`
+* Linux: `~/.arduino15/packages/arduino/hardware/avr/1.8.6/firmwares/atmegaxxu2/arduino-usbserial`
+
+You can also access the files from the [board package repository on GitHub](https://github.com/arduino/ArduinoCore-avr/tree/master/firmwares/atmegaxxu2/arduino-usbserial).
+
+Do one of the following:
+
+* Ensure that that **Arduino AVR Boards** package has been installed using Arduino IDE or Arduino CLI.
+* [Download the firmware for your board from GitHub](https://github.com/arduino/ArduinoCore-avr/tree/master/firmwares/atmegaxxu2/arduino-usbserial).
+
+Use the table below to find the correct firmware to use for your board:
+
+| Board                 | Serial chip | Firmware                                       |
+|:----------------------|:------------|:-----------------------------------------------|
+| Arduino UNO R3        | Atmega16U2  | Arduino-usbserial-atmega16u2-Uno-Rev3.hex      |
+| Arduino Mega2560 Rev3 | Atmega16U2  | Arduino-usbserial-atmega16u2-Mega2560-Rev3.hex |
+| Arduino MegaADK Rev3  | Atmega16U2  | Arduino-usbserial-atmega16u2-MegaADK-Rev3.hex  |
+| Arduino UNO (R1/R2)   | Atmega8U2   | Arduino-usbserial-uno.hex                      |
+| Arduino Mega          | Atmega8U2   | Arduino-usbserial-mega.hex                     |
+
+---
+
+## 2. Connect your board with the Atmega16U2/8U2 in DFU mode
+
+To enable DFU programming, the Atmega16U2/8U2 chip needs to be reset to DFU mode.
+
+<!-- UNO (Rev3 or earlier), and Mega boards use either an Atmega16U2 or Atmega8U2 chip as a USB-to-serial converter. By setting a board to **DFU mode** (Device Firmware Update) you can [upload USB-to-Serial firmware to the chip](https://support.arduino.cc/hc/en-us/articles/4408887452434-Flash-USB-to-serial-firmware-in-DFU-mode). -->
+
+Follow these steps:
+
+1. Connect the board to your computer
+
+1. **If you're using a "Rev 1" board:** If you're using an older revision (UNO Rev1 or Mega Rev1), you need to also assert and hold the **HWB line**. Find the two HWB pads on the back of the board and short them using something conductive, like a piece of wire.
+
+   ![The HWB pads on the UNO Rev1.](img/UNO-DFU-HWB-line.png)
+
+1. Find the RESET and GND pins for the ATmega USB-Serial Processor. They are the innermost two pins of the six located close to the USB port.
+
+   ![The RESET and GND pins for the ATmega USB-Serial Processor.](img/UNO-DFU-reset-pins.png)
+
+1. Short the pins using a jumper cable or other  (follow [these instructions](#rev1) for UNO Rev1).
+
+1. Short the RESET and GND pins to reset the board.
+
+1. Release or remove any wires or other material before proceeding to the next step.
+
+---
+
+## 3. Program the chip
+
+You can flash the firmware using dfu-programmer (recommended) or the original Atmel FLIP application (Windows only).
+
+In this section:
+
+* [Using dfu-programmer](#using-dfu-programmer)
+* [Using Atmel FLIP](#using-atmel-flip)
+
+### Using dfu-programmer {#using-dfu-programmer}
+
+<a id="using-dfu-programmer-(macos%2Flinux)"></a> <!-- Maintain old anchor links -->
+
+**[dfu-programmer](https://github.com/dfu-programmer/dfu-programmer)** is a lightweight, multi-platform command-line programmer that implements the Atmel FLIP USB DFU Protocol[^1].
+
+[^1]: [The Atmel FLIP USB DFU protocol](https://ww1.microchip.com/downloads/en/AppNotes/doc8457.pdf) is based on part of official USB DFU specification, but does not implement it entirely. For this reason, Atmega16U2 or Atmega8U2 chips cannot be used with **dfu-util** or other tools that implement the main USB DFU specification.
+
+Follow these steps:
+
+1. Install dfu-programmer:
+
+   * **Windows:** Download [the latest dfu-programmer release from GitHub](https://github.com/dfu-programmer/dfu-programmer/releases).
+
+   * **macOS:** dfu-programmer requires the **libusb library** (libusb-1.0.0) to run. Manually installing libusb is complicated, so it's highly recommended to install dfu-programmer using the [homebrew package manager](https://brew.sh/), which will include libusb-1 as a dependency.
+
+     When homebrew is installed, run this command in Terminal to install dfu-programmer:
+
+     `brew install dfu-programmer`
+
+   * **Linux:** Run this command in Terminal to install dfu-programmer:
+
+     `sudo apt-get install dfu-programmer`
+
+1. Open your system's command line application.
+
+1. If you downloaded dfu-programmer from GitHub, move into the surrounding folder (for example, the Downloads folder):
+
+   * Windows (cmd): `cd %USERPROFILE%\Downloads`
+   * macOS/Linux: `cd ~/Downloads`
+
+1. Erase the memory (replace `<atmegaxxu2>` with either `atmega8u2` or `atmega16u2`).
+
+   * Windows: `dfu-programmer.exe <atmegaxxu2> erase`
+   * macOS/Linux: `dfu-programmer <atmegaxxu2> erase`
+
+1. Flash the firmware:
+
+   * Windows: `dfu-programmer <atmegaxxu2> flash <firmware path>`
+   * macOS/Linux: `dfu-programmer <atmegaxxu2> flash <firmware path>`
+
+1. Disconnect and reconnect the board to your computer.
+
+<!--
+
+* **Example: UNO R3 (Windows):**
+  ```
+  TODO
+  ```
+
+* **UNO R3 (macOS/Linux):**
+  ```
+  dfu-programmer atmega16u2 flash ~/Library/Arduino15/packages/arduino/hardware/avr/1.8.6/firmwares/atmegaxxu2/arduino-usbserial/Arduino-usbserial-atmega16u2-Uno-Rev3.hex
+  ```
+
+* **Mega2560 Rev3 (Windows):**
+  ```
+  TODO %localappdata%
+  ```
+
+* **Mega2560 Rev3 (macOS/Linux):**
+  ```
+  dfu-programmer atmega16u2 flash ~/Library/Arduino15/packages/arduino/hardware/avr/1.8.6/firmwares/atmegaxxu2/arduino-usbserial/Arduino-usbserial-atmega16u2-Mega2560-Rev3.hex
+  ```
+
+-->
+
+#### Example commands for dfu-programmer
+
+> [!NOTE]
+> The examples assume that version 1.8.6 of Arduino AVR Boards is installed.
+
+##### UNO R3 on Windows
+
+```
+dfu-programmer.exe atmega16u2 flash %USERPROFILE%\AppData\Local\Arduino15\packages\arduino\hardware\avr\1.8.6\firmwares\atmegaxxu2\arduino-usbserial\Arduino-usbserial-atmega16u2-Uno-Rev3.hex
+```
+
+##### UNO R3 on macOS
+
+```
+dfu-programmer atmega16u2 flash ~/Library/Arduino15/packages/arduino/hardware/avr/1.8.6/firmwares/atmegaxxu2/arduino-usbserial/Arduino-usbserial-atmega16u2-Uno-Rev3.hex
+```
+
+##### UNO R3 on Linux
+
+```
+dfu-programmer atmega16u2 flash ~/.arduino15/packages/arduino/hardware/avr/1.8.6/firmwares/atmegaxxu2/arduino-usbserial/Arduino-usbserial-atmega16u2-Uno-Rev3.hex
+```
+
+##### Mega2560 Rev3 on Windows
+
+```
+dfu-programmer.exe atmega16u2 flash %USERPROFILE%\AppData\Local\Arduino15\packages\arduino\hardware\avr\1.8.6\firmwares\atmegaxxu2\arduino-usbserial\Arduino-usbserial-atmega16u2-Mega2560-Rev3.hex
+```
+
+##### Mega2560 Rev3 on macOS
+
+```
+dfu-programmer atmega16u2 flash ~/Library/Arduino15/packages/arduino/hardware/avr/1.8.6/firmwares/atmegaxxu2/arduino-usbserial/Arduino-usbserial-atmega16u2-Mega2560-Rev3.hex
+```
+
+##### Mega2560 Rev3 on Linux
+
+```
+dfu-programmer atmega16u2 flash ~/.arduino15/packages/arduino/hardware/avr/1.8.6/firmwares/atmegaxxu2/arduino-usbserial/Arduino-usbserial-atmega16u2-Mega2560-Rev3.hex
+```
+
+### Using Atmel FLIP {#using-atmel-flip}
+
+<a id="using-flip-(windows)"></a> <!-- Maintain old anchor links -->
+
+Before you begin:
+
+1. Open Device Manager.
+
+1. Expand the **libusb-win32-devices** category. If it is missing, [follow these steps](#install-libusb-win32) before proceeding.
+
+1. Take a note of the device name, which should be either **ATmega16U2** or **ATmega8U2**.
+
+Now flash the firmware using FLIP:
+
+1. Download and install [FLIP](https://www.microchip.com/en-us/development-tool/flip).
+
+1. Open FLIP.
+
+    > [!NOTE]
+    > Opening the application may prompt a 'Could not find a Java Virtual Machine' error. In this case, [install Java Runtime Environment](https://www.java.com/en/download/manual.jsp) with the **Windows Online** option.
+
+1. Select the device name you identified earlier (ATmega16U2 or ATmega8U2).
+
+1. Click the Cable button, select USB, then click Open.
+
+    ![Flip USB Selection](img/Flip_USB_Selection.png)
+
+1. In the menu, click _Device > Select..._
+
+    ![Flip Device Selection](img/Flip_Device_Selection.png)
+
+1. Click _File > Load HEX File..._
+
+1. Select your driver `.hex` file and click 'OK'.
+
+1. For Operational Flow, check **Erase**, **Program**, and **Verify** (this is the default setting).
+
+    ![Operational flow selections.](img/atmel-flip-operational-flow.png)
+
+1. Click on the 'Program Target Device Memory' button.
+
+    ![Program Target Device Memory](img/Flip_Program_Target_Device_Memory.png)
+
+1. The firmware will be flashed, which may happen very quickly. A "Programming done" message should be displayed in the bottom-left corner.
+
+    ![Programming done in 0 seconds.](img/atmel-flip-done.png)
+
+1. Disconnect and reconnect the board to your computer.
+
+#### Install the libusb-win32 driver in Device Manager {#install-libusb-win32}
+
+1. Look for an **Unknown Device** under 'Other Devices'. Disconnect all devices except the board if multiple unknown devices are available.
+
+2. Right-click and select **Update driver**.
+
+   ![Device manager window with "Update driver" selected in menu](img/atmel-device-manager-update-driver-1.png)
+
+3. Point to `C:\Program Files (x86)\Atmel\Flip 3.4.7`
+
+4. Click 'Install' and wait for the installation to complete.
+
+   ![Windows Security pop-up](img/atmel-device-manager-update-driver-2.png)
+
+5. The device should now be recognized, under 'libusb-win32-devices'
+
+   ![Device manager with "ATmega16U2" selected](img/atmel-device-manager-update-driver-3.png)