user6781: I'm looking for a complete pinout of the Arduino Ethernet R3.
I've found one here which is low quality, and seems not complete (where are the digital I/O pins?).

BTW, it was not a good idea for Arduino to name this board "Arduino Ethernet", as this is pretty useless for searching online :-(

user66021: That's a better one from :
https://pinoutguide.com/images/arduino/ethernet.png
This one also presents the Arduino Ethernet R3 board and 
has the extra I2C pins (SCK=A5,SDA=A4) next to the AREF pin.


user630: The formal Arduino.cc website mentions, somewhat obscurely, that the Arduino Ethernet is pin compatible with Arduino Uno:

The Revision 3 of the board introduces the standardized 1.0 pinout

Except for pins 10-13:

Pins 10, 11, 12 and 13 are reserved for interfacing with the Ethernet
  module and should not be used otherwise. This reduces the number of
  available pins to 9, with 4 available as PWM outputs.

The other difference is the onboard LED is connected to pin 9 rather than the Uno's pin 13:

On most other arduino boards, this LED is found on pin 13. It is on pin 9 on the Ethernet board because pin 13 is used as part of the SPI connection.

You can use any Arduino Uno pinout diagram as a reference, the one you have found seems to be pretty elaborated. 

6781: <p>I'm looking for a complete pinout of the <a href="http://arduino.cc/en/Main/arduinoBoardEthernet" rel="nofollow noreferrer">Arduino Ethernet R3</a>.
I've found one <a href="http://f1mvp.perso.sfr.fr/Robotic/arduino.htm" rel="nofollow noreferrer">here</a> which is low quality, and seems not complete (where are the digital I/O pins?).</p>

<p><img src="https://i.stack.imgur.com/9mk4A.jpg" alt="enter image description here"></p>

<p>BTW, it was not a good idea for Arduino to name this board "Arduino Ethernet", as this is pretty useless for searching online :-(</p>
 66021: <p>That's a better one from :</p>

<p><a href="https://pinoutguide.com/images/arduino/ethernet.png" rel="nofollow noreferrer">https://pinoutguide.com/images/arduino/ethernet.png</a></p>

<p>This one also presents the Arduino Ethernet R3 board and 
has the extra I2C pins (SCK=A5,SDA=A4) next to the AREF pin.</p>

<p><a href="https://i.stack.imgur.com/QLJqj.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/QLJqj.png" alt="enter image description here"></a></p>
 630: <p>The <a href="http://arduino.cc/en/Main/arduinoBoardEthernet" rel="nofollow noreferrer">formal Arduino.cc website</a> mentions, somewhat obscurely, that the Arduino Ethernet is pin compatible with Arduino Uno:</p>

<blockquote>
  <p>The Revision 3 of the board introduces the standardized 1.0 pinout</p>
</blockquote>

<p>Except for pins 10-13:</p>

<blockquote>
  <p>Pins 10, 11, 12 and 13 are reserved for interfacing with the Ethernet
  module and should not be used otherwise. This reduces the number of
  available pins to 9, with 4 available as PWM outputs.</p>
</blockquote>

<p>The other difference is the onboard LED is connected to pin 9 rather than the Uno's pin 13:</p>

<blockquote>
  <p>On most other arduino boards, this LED is found on pin 13. It is on pin 9 on the Ethernet board because pin 13 is used as part of the SPI connection.</p>
</blockquote>

<p>You can use any Arduino Uno pinout diagram as a reference, the <a href="http://marcusjenkins.com/wp-content/uploads/2014/06/ARDUINO_V2.png" rel="nofollow noreferrer">one you have found</a> seems to be pretty elaborated. </p>
