ATMEGA2560-16U vs ATMEGA2560V-8AU - Bootloader Issues and more

[cornerpocket]

Hello, I am having issues with some of the chips I ordered. Disclaimer beforehand that I am still new to this so I'm doing my best to explain.

I've been using these, which usually have the ATMEGA2560-16U chip like in the product picture. I received a batch of 18 of these from my last order, and 11 of them have a ATMEGA2560V-8AU chip, and coincidentally I'm having issues with all the boards with that chip.

In the datasheet on digikey, I found this part which seems to indicate a clear difference between the two:

Speed Grade:
– ATmega640V/ATmega1280V/ATmega1281V:
• 0 - 4MHz @ 1.8V - 5.5V, 0 - 8MHz @ 2.7V - 5.5V
– ATmega2560V/ATmega2561V:
• 0 - 2MHz @ 1.8V - 5.5V, 0 - 8MHz @ 2.7V - 5.5V
– ATmega640/ATmega1280/ATmega1281:
• 0 - 8MHz @ 2.7V - 5.5V, 0 - 16MHz @ 4.5V - 5.5V
– ATmega2560/ATmega2561:
• 0 - 16MHz @ 4.5V - 5.5V

I can't find any pictures online anywhere of these little MEGA PRO 2560 embed chips having anything but the ATMEGA2560-16U.

When I try uploading code in the Arduino IDE, I get byte mismatch errors. When I researched the errors, I bought a USBAsp device. I tried burning the bootloader and uploading the program using the programmer with ICSP pins connected, and I've also tried the Arduino programmer "Gammon" script using another Arduino as the programmer.

I can't seem to get these ATMEGA2560V-8AU boards to work. Strangely, I managed to get my sketch uploaded to one of them, and it seems to function, but when I try uploading Blink or something, it gives me avrdude byte mismatch errors again. However, on that particular board, even with the errors, sketches seem to upload and work. All other boards I have tried that usually isn't the case.

At first I thought maybe the ATMEGA2560V-8AU chips aren't meant to be mated with the Arduino MEGA 2560 setup and the factory made a mistake putting those chips on there. (Also reinforced by the fact I can't find any reference to those boards existing with these chips, and the different specs in the datasheet). However, since I have one of them semi-working, it makes me think I can still somehow make these work.

I'm still learning and can't quite make sense of it. Did I get ripped off and sold bad boards with cheaper chips? Is there some way to burn bootloaders on these 2560V chips to make them work? I'd appreciate any tips.

One last note, all of these 2560V boards show up as Board Unknown when I try to view the Board Info in the Arduino IDE.

[markd833]

My Microchip datasheet for the ATmega640/V-1280/V-1281/V-2560/V-2561/V (doc no 2549Q–AVR–02/2014) indicates that the V variants are 8MHz parts (as opposed to the more usual 16MHz parts).

Section 31.2 (Speed Grades) confirms that the V variants are indeed good for 8MHz. There is no mention of 16MHz for the V variants.

The bootloader you are trying to load may be configured for 16MHz parts. If that's the case, then all the timings will be off including baud rates etc. You can probably load over ICSP as that isn't dependant on baud rates etc.

I'd send the V variant boards back to your supplier and request the 16MHz parts that they were advertising. There are comments left by other buyers that suggest they may also have received a mix of 2560 and 2560V parts.