How exactly does this pull-up resistor work?

Question

Electronics

Hello. Could you explain, if possible, exactly how this pull-up resistor works? It goes to the Reset input of the microcontroller.
I understand it this way - when the supply voltage is applied (in my case 3.3V), then it pulls up this voltage and a high level signal is always kept at the Reset input (even with slight fluctuations in the supply voltage). Accordingly, if Upit = 0, then the input signal is low, which in fact resets the MK.
And yet, does it make sense to make a key? I looked at the debug boards for this MK, there is only a pull-up resistor on the reset. But when the connector is connected, there is an output for reset, which means, as I understand it, the possibility of an external reset of the MK. How does an external reset happen if there is no key there?
Well, maybe I misunderstand all this, I will be glad if you explain. Thank you very much!

Answer 1

I understand it this way - when the supply voltage is applied (in my case 3.3V), then it pulls up this voltage and a high level signal is always kept at the Reset input (even with slight fluctuations in the supply voltage).

That's right, it is needed to set a high level on the Reset signal after turning on the device.

Accordingly, if Upit = 0, then the input signal is low, which in fact resets the MK.

When there is no power on the board, resetting the MK is usually not required; without power, the MK turns itself off. The resistor is just needed to set the logical unit at the Reset input

And yet, does it make sense to make a key? I looked at the debug boards for this MK, there is only a pull-up resistor on the reset. But when the connector is connected, there is an output for reset, which means, as I understand it, the possibility of an external reset of the MK. How does an external reset happen if there is no key there?

A pull-up resistor is so called because it "pulls up" the voltage. Because of its high impedance (10 kΩ), another signal source easily "overpowers" the pullup. This is exactly how the external Reset signal works - despite the pullup resistor, applying a logic zero to Reset causes it to go low.

Answer 2

The input of the CMOS cell has a very high resistance, which makes it very sensitive to interference and can respond to random charges and parasitic currents.
therefore, there is a recommendation that inputs that are not connected anywhere should be pulled with a resistor to VCC or GND.

Answer 3

If an external reset of the microcontroller is not planned, then this resistor is not needed, you can simply connect RESET to the power bus. The resistor makes it possible to pull RESET to ground to an external device (using a transistor, a button, etc.), such as a programmer. In general, there are different options for connecting something to the reset pin, you need to look at the datasheet of a specific microcontroller.