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:

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...