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?