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For the discussion of Arduino related topics.
By pennig
I've got a 2560, and when I plug it into my Mac (running OS X 10.6.4), nothing appears in /dev/tty* to indicate that the board is recognized. Consequently, I can't upload sketches to it. On my Windows machine, attaching it results in an "Unknown Device" notification, and I can't successfully install the .inf.

Is there something I can do to fix it? If not, can I return it for a replacement?

The board is powered when plugged in, and the factory-installed sketch runs fine (LED blinks), so maybe it's just the Atmega8U2 chip...
By pbender
This is a side effect of the new USB interface chip that the UNO and Mega 2560 have.

On my Linux box, the UNO I bought a few weeks ago shows up as /dev/ttyACM0. This isn't a serial port that
RXTX searches by default (RXTX is the serial interface library used by the Arduino environment). The quick
and dirty workaround on a Linux machine is to make a symbolic link from /dev/ttyUSB0 to /dev/ttyACM0.
/dev/ttyUSB0 is a port that RXTX looks for.

I don't know what the solution is on a MAC, but I know the device name should include ACM in the name
instead of USB.