user20049: I have been reading a bit about the internal pullup resistor. I know from past projects in school that resistor themselves are fragile (burnt one by accident due to higher current than was made for).
I have two different Arduino models. One by Intel and rest are standard Arduino Uno.
So I was wondering about safely using the internal pullup resistor on the Arduino Uno. Hence my question is about the internal pullup resistor pinmode; How many pin can you connect to it safely and not overload it?

user21015: Each pin has its own, separate, pullup resistor. 
I don't believe you can damage it by drawing current from the port, because the pullup resistor is only active when the port is in high impedance (hi-Z, input) mode. 
The pullup resistor can be damaged by overvoltage, static discharge, and the like. 
The Uno has 20 kOhm pullup resistors according to this tutorial. If you feed it a 0V signal while the Atmega is running at 5V, the current will be a quarter of a milliamp, which is miniscule.

20049: <p>I have been reading a bit about the internal pullup resistor. I know from past projects in school that resistor themselves are fragile (burnt one by accident due to higher current than was made for).</p>

<p>I have two different Arduino models. One by Intel and rest are standard Arduino Uno.</p>

<p>So I was wondering about safely using the internal pullup resistor on the Arduino Uno. Hence my question is about the internal pullup resistor pinmode; How many pin can you connect to it safely and not overload it?</p>
 21015: <p>Each pin has its own, separate, pullup resistor. </p>

<p>I don't believe you can damage it by drawing current from the port, because the pullup resistor is only active when the port is in high impedance (hi-Z, input) mode. </p>

<p>The pullup resistor can be damaged by overvoltage, static discharge, and the like. </p>

<p>The Uno has 20 kOhm pullup resistors according to <a href="https://www.arduino.cc/en/Tutorial/DigitalPins" rel="nofollow">this tutorial</a>. If you feed it a 0V signal while the Atmega is running at 5V, the current will be a quarter of a milliamp, which is miniscule.</p>
