OK - weird question here: Is it possible to download the contents of an ATmega168/328, essentially backing it up so that it can somehow be restored later?

For example: Let's say I have lost the source code to a very useful program currently residing on a 328, but I need to flash it with a different sketch temporarily, then restore that original sketch. This would be useful in the case that the chip was soldered directly onto a board - a big mess to try to replace.

Is this possible in some way, perhaps by altering an ISP programmer?
Just curious.
-Emo

Hi Emo,
Generally yes, it is possible. It's straightforward using avrdude and any ISP programmer. We use this method for production programming of our kits-- we program a chip "just right" and then read it out, and re-flash that onto many (for example) Bulbdial chips.

Here's the exception: It is possible to *lock* an AVR such that the memory contents cannot be read out without erasing the chip, using the "lock bits," which are EEPROM bits similar to the usual fuse bytes. This is a feature designed to prevent just anyone from stealing your program from a finished product. If your chip has been locked in this way, you cannot read out the memory.

We've posted a new article on our blog about this question.

I read the article and it answered most of my questions. However, I have just one quick question"

The article says

It is possible to intentionally lock the contents of the flash memory, such that the contents cannot be read out*. You can do this by setting the lock bits of the AVR according to the values listed in the datasheet, and the lock bits cannot be reset except by erasing the whole device.

So if I need to reset the lock bits, then I need to erase the whole device? Is there another way around this?

Not that I know of.