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I would like to know what the exact difference is between the Uno and Mega boards and the older boards (Duemilanove, Diecimila, etc.). Why do I need to install a FTDI driver for the older boards, and not for the Uno/Mega boards? I was in a class the other day, using the Nano, and the lecturer recommended the FTDI drivers. The Nano is a newer type board, so why does that require a driver? I've just discovered that the Nano is old tech from 2008, after reading Are there any reasons to pick Nano over Micro?

What is it about the Uno and Mega boards that don't require the FTDI to be separately installed?

I see that the Getting Started w/ Arduino on Mac OS X page states that the older boards use the FTDI chip. Does that imply that the Uno/Mega boards do not? If they do not, then what do they use?

I have a vague notion that some USB sticks, keyboards, mouse and other various USB devices may contain a driver within the circuitry/firmware(?) of the device, which when connected to a PC for the first time, can be used to install the driver without the PC needing to access the web for the driver. Is this what the difference is between the UNO/Mega and the older devices? If so, is it possible to modify, or flash the firmware of the older boards so that they can connect without the need for an FTDI driver?

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The older Arduino boards used an FTDI FT232R chip to handle the USB port. This chip is a special purpose, USB to serial UART interface.

In the current Arduino boards, the USB to serial conversion is handled by dedicated Atmel Atmega8u2 processor. This is a processor that is similar to the main ATmega328p processor, but the added benefit of having built-in USB capabilities.

So, why the change? Well, first, it's cheaper than the FTDI chip, and second, it can do much more. Being that it's an actual microprocessor, you can actually reprogram this chip to behave like different USB devices. For example, you can reprogram it to make your Arduino look like a keyboard, a joystick, a thumb drive, a MIDI instrument - anything that you can do via USB. The FTDI chip does not have this capability, and so it can only ever look like a serial COM port to your PC.

Why have 2 microprocessors on the Arduino? By having a dedicated processor to handle the USB communication, it keeps the main processor free to run your sketches. Plus, the Arduino team felt that this design keeps the Arduino more "hackable".

Wouldn't it be cheaper to make a board using just the one processor that has built-in USB? Yes! That is exactly what the Arduino Leonardo is. It uses the Atmega32U2, the big brother to the Atmega8U2.

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