I've downloaded the data sheet (from datasheetcatalog.com), and this
does a decent job of explaining what the pins are. It does leave some
questions unanswered, though:
You can also download the datasheet directly from
Atmel.com
1. What voltage should I connect to Vcc? It seems to imply that it can
work at 5V or 3.3V, but no actual limits are given.
The Atmega48 is available as both a 5V and 3.3V versions, as well as a
1.8V version I believe. Where did you get your chip, and what part number is printed on it? If the chip came as part of a hobby kit of some sort, then I might go out on a limb and suggest that it is a 5V part. However hooking 5V to a low voltage part will damage it, so be sure before you power up or you might be out $2.69 or so.
2. It says that AVCC should be connected to Vcc, but "if the ADC is
used, it should be connected to VCC through a low-pass filter". I'm
still new to electronics -- what does this mean? I'm guessing a
capacitor, but what size and connected exactly how? (The schematic at
<
http://www.nongnu.org/avr-libc/user-manual/group__demo__project.html>
doesn't seem to show such a connection.)
If you aren't using the analog to digital converter, or you don't care much about the accuracy of your voltage readings, then just connect the pin to Vcc and be done. The ADC uses an isolated power supply so that all of the switching noise on Vcc doesn't corrupt the voltage readings. There is an example filter using an inductor and capacitor on page 252 of the datasheet (mine is marked Rev. 2545K–AVR–04/07).
Erm... I think that's all for now. No wait, one more: this shiny new
AVR-ISP2 on my desk is a USB device. I've never seen a USB device that
didn't require drivers hooked into the kernel (unlike serial devices,
alas). But nobody I've talked to has mentioned this, or where I would
download OS X drivers for it... can other Mac users here comment on the
necessity & availability of drivers for this ISP?
I am sure it needs drivers, but I haven't used this device before...
-Matt