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I have a brand new board which is a clone of the Mega2560. I need to install the USB firmware on the 16U2 and the bootloader on the 2650 chip. I have Atmel Studio and a JTAGICE-3. Using those, I can download HEX files compiled with the Arduino IDE, and they run successfully.

But I'm having trouble finding Mega-specific instructions for getting the firmware installed so that I can use the Arduino ISP protocol for downloading new sketches. I can find much more information about the Uno than the Mega. And much of the information I do find seems to be dated.

1) Which are the right files to download?
I've tried to install the 'MEGA-dfu_and_usbserial_combined.hex' to the 16U2 and the 'stk500boot_v2_mega2560.hex' to the 2560.

But the IDE won't connect via AVR ISP, and I get no serial communications from a serial sample sketch downloaded with the ICE.

2) What are the correct Fuse settings after I flash those files?

3) Is there a good way to confirm that the 16U2 USB converter is working correctly in isolation from the 2560 chip?

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Let focus on one thing at a time, that is flashing the 16u2. You can see if you've successfully done that when you can see the Arduino in your device-manager.

First of, MEGA-dfu_and_usbserial_combined.hex is, as stated on the github page, for the 8u2, not the 16u2. Since you already have a ISP programmer you don't need the dfu functionality. You can just flash the precompiled Arduino-usbserial-atmega16u2-Mega2560-Rev3.hex file.

The fuses can also be found in the readme.txt on github: -U lfuse:w:0xFF:m -U hfuse:w:0xD9:m -U efuse:w:0xF4:m -U lock:w:0x0F:m. I don't see any difference in the fuses between the 8u2 and 16u2, so they should work for the 16u2 too.

Hope this helps.

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  • Thank you. Is there any reason not to include the DFU?
    – AShelly
    Commented Jul 13, 2014 at 13:13
  • dfu is needed if you want to reprogram the 16u2 over usb. First you'll probably never have to update it. Second you already have a JTAG programmer, so you can use that one. Thirdly, to get the dfu version for the 16u2 you'll have to compile it yourself, as it isn't present precompiled in the github repository. (And it needs LUFA to compile). So in short, it's just not worth the trouble.
    – Gerben
    Commented Jul 13, 2014 at 14:54

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