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I'm a newbie in Arduino and I bought an Arduino Mega instead of the Uno. I want to know what the so-called additional i/o pins do. Are they the same with PWM and SPI? What can they do?

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    Do a google image search for "arduino mega pinout" - there's thousands of results that show you exactly what each and every pin can do. – Majenko Dec 29 '15 at 11:28
  • When asking "obvious" questions it helps to explain what you've done to find an answer for yourself – then explain why you are still confused. That way we have a better idea about your question. – dlu Jan 1 '16 at 9:13
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Firstly some background info on the Arduino Mega:

I haven't used the Mega, but I've used the Uno, and have worked with a variety of ATmega microcontrollers.

First thing you need to know is that the Arduino Mega (or any other Arduino) is a board that uses the Atmel ATmega microcontrollers. The specific microcontroller used on the Mega is the ATmega1280 ATmega2560.

So if you are keen to learn more about your Arduino, a good place would be to look at the datasheet of the microcontroller itself. Just google ATmega1280 ATmega2560 datasheet.

However this might be a fair bit complicated, since you are new to the Arduino and microcontroller world.

A good place to start would be the Arduino website itself (but I suppose you've already looked at it).

Now, regarding your question:

I'm not sure what you are referring to as "additional i/o pins", but here's a quick rundown on what I/O pins are and used for.

As you may know I/O pins are used by the microcontroller to talk to the outside world. On the ATmega chips, most of these are GPIOs (General Purpose I/Os) that can be programmed to receive or send digital signals. Of these GPIOs some are used for PWM, and some may be used for some communication protocol. And of course there are analog input & reference pins, voltage supply, ground etc.

You can find all this information in the datasheet I linked above.

If you are curious how Arduino has routed the pins, you can have a look at the schematic of the Arduino Mega here.

If you also have a look at the Arduino website, they have a very good description on what each pin does: Arduino Mega.

Look at "Inputs and Outputs".

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    Even though the poster said he bought an "Arduino Mega", what he almost certainly bought is an Arduino Mega 2560, so the microcontroller in question is an ATmega2560 (Identical to the ATmega1280, except that it has twice the flash capacity). – microtherion Dec 29 '15 at 21:15
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Additional I/O pins means more inputs and outputs. Therefore, you can have more signals. There are also some more specialized pins. For example, there are more PWM pins, more TX and RX pins for serial communication and more analog read pins.

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