The Arduino Duemilanove with ATMega328 and that Reset Line

This one is a small followup to my earlier discussion of how to pop of the capacitor of an Arduino Diecimilia so you can both disable the auto-reset and use debugWIRE.

At the time I did that post I had Duemilanove’s in my posession but I was doing the project with the Diecimila, so I didn’t really go into that board. The Duemilanove has the advantage of not having to change a jumper for the DC power/USB power, as it auto-switches.

In the documentation page for the Duemilanove. they discuss the auto-reset line (not in the context of debugWIRE, but it’s the same thing):

The Duemilanove contains a trace that can be cut to disable the auto-reset. The pads on either side of the trace can be soldered together to re-enable it. It’s labeled “RESET-EN”.

I never made the mod to any of my Duemilanoves as I never needed it, but certainly nicer than the “pop off the capacitor” method, since it’s reversible with just a soldering iron and doesn’t require you to re-solder the chip capacitor. I’ve also wondered if you could solder a jumper onto the pads and so be able to enable/disable the auto-reset/debug at will.

But never mind that. A couple of days ago I got a new batch of Duemilanoves for projects. These ones I ordered were the ones that advertised that they were the ATMega328 version (as opposed to the ATMega168 on the Diecilimia and original Duemilanove). Here’s a look at the top and bottom.

Top View


The board is marked with the appropriate logos and such, and I bought it from a reputable place, so I think it’s an authentic Duemilanove, as opposed to a workalike from the same design (there are lots of Arduino clones, since it’s open design, and there’s nothing wrong with them).

So I was working with this one today, and I thought, “huh, this looks different”. I lined it up against one of my existing Duemilanoves.

Old Duemilanove on Top, ATMega328 Version on bottom

I didn’t see it at first, either. Here, let me point it out.

RESET-EN pads are missing from ATMega328 Version

Yep, the newer ATMega328 version of the board (which shouldn’t be any different other than the chip plugged in the socket) is missing those “RESET-EN” pads. That’s disappointing.

Here’s a couple of views under my microscope, since I like using my microscope.

Original Duemilanove with pads
Pads missing from the ATMega328 version

The hardware reference page doesn’t mention this change.

What does this mean? Well, nothing really. Board still works fine, and you get the ATMega328 for more space. It just means that if you want to do the auto-reset/debugWIRE changes, you’re back to doing them by my “Pop off the capacitor” method. Have fun.