Merge pull request #292 from arduino/I2C-and-pull-up-resistors

I2C and pull up resistors [HC-1398]

Author: Renat0Ribeir0

content/Hardware Support/Generic/I2C-and-pull-up-resistors.md

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+---
+title: "I2C and pull-up resistors"
+id: 4402394268562
+---
+
+For effective data transmission with the Inter-Integrated Circuit (I2C) protocol using Arduino, it's often necessary to use external pull-up resistors on the designated I2C pins. Most Arduino boards don't have pre-installed pull-up resistors on these pins, but instead they offer exposed pads for surface mount resistors ("SMD"). This gives more flexibity on how these pins can be used. More specifically:
+
+* The I2C designated pins can also be used as General Purpose Input/Output (GPIO) pins or for Analog-to-Digital Conversion (ADC). In this modes, pull-up resistors are not typically required.
+* Users are not bound to use I2C with pre-set pull-up values. This is important because the optimal pull-up value can vary depending on different factors.
+
+   <a class="link-external" href="https://learn.sparkfun.com/tutorials/i2c/i2c-at-the-hardware-level">Read more about I2C and pull-up values</a>
+
+Therefore, when setting up I2C communication it is important to refer to the specifications and device datasheets for understanding the ideal pull-up value requirements.