Where can I find a hardware manual (or documentation) for Arduino Uno & ATMega328P?

Question

Where can I find a hardware manual (documentation or a book) for Arduino board?

As far as I know, all hardware details are dispersed (or scatter) in different tutorials.

Answer 1

The Arduino Uno is little more than an ATmega328P microcontroller. In most cases you will be interested by the documentation of the microcontroller itself. Anyway, here are both:

• The Arduino Uno product page contains the most basic specs, as well as links to
  • the board schematic
  • the pin mapping, but see below for a nicer alternative
• the ATmega328P product page links to
  • the ATmega328P family datasheet, a 650 page authoritative document
  • the ATmega328P Automotive - Complete Datasheet, specific to the Uno's chip.
  • the AVR instruction set manual, for those who want to play with assembly
  • many application notes discussing specific uses of some peripherals

Alberto (aka PighiXXX) has published nicer versions of the Arduino Uno pinout:

enter image description here

• aaa: I've added the "Arduino specific" guides/help from Arduino.cc, since it's not a completely new answer. Feedback is appreciated, I can revert it/create my own answer if neccesary.
• Edgar Bonet: @Paul: The question is about the hardware of the Arduino Uno, and the OP specifically wrote he is looking for reference material (manual, documentation or book) rather than tutorials. The links you added are very general. They are not specific to the Uno hardware, and they tend to cover the software more than the hardware.
• aaa: Oops! I have reverted my adjustments, it didn't add value to this specific question.

Answer 2

For the hardware part, you can refer to the schematic. It shows all the components so you can find their datasheets for detailed study.

UNO schematic

But to me, if you're just using the board but not designing your own board or writing libraries for the board, I don't think this is necessary. Stick to application level or IO-level and only really dig into the hardware when you're blocked when doing things like using all timers, low-power mode, interrupt with Serial...