Re: Danger of Overcurrent when connecting INPUT_PULLUP pin directly to ground?

5V/20K = 0.25mA (250uA).
Shorting the Input to Gnd merely takes away the 1uA the input pin needs for a high.

The internal pullup provides no protection if the pin is set to Output, commanded to High and then shorted to Gnd.
If left shorted, it will blow the output drive transistor sooner or later.

I have an Arduino Due 3.3v.
I plan to configure digital output pins and connect them to inputs I1 to I8 of a UND2981A IC to control frequency inverters.

  1. a From your previous answer, I understand that external pull resistors are not required.
    Can you confirm that for me?

1)b) Nevertheless, external pulling resistances did not improve the free passage between HIGH and LOW ?

  1. I have code parts to bypass when a switch is closed,
    So the best way is to configure the output pin and connect it to the GND and don't forget the 10kohms external pull-up resistor ?

Thank you for your technical advice
UDN2981A et VAR.jpg

UDN2981A et VAR.jpg

Please don't post on someone else's thread, this is a completely different question about a different Arduino and nothing to do with input pullups - start your thread, don't piggyback a different one.

Per its datasheet

the device needs <0.5mA of input drive current. Pullup resistors on the inputs are not needed

The output Sources current (supplies current to the load, vs sinking current from the load).
So if you had a resistor to Gnd on the output, it looks like a power supply. A pullup resistor does nothing in this case.
(If the device was a current sink, then it would act like Gnd connection was being made when it turned on).

Your schematic, are points I draw arrows connection points only? Are they connected to Gnd?

I think that you are expecting the UDP2981A output to be Low to act as a Gnd when SW2 is connected to 24V.
It will not do that. It can only drive its output High: