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Totem pole pull up resistor

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Jr.Maxwell:
Hello,

I'm new to microcontrollers and trying to master how to deal with it's pins. I would like to know if there are any applications where I use pull up resistors in totem poles? And why is there even tri state- when will I ever want a pin in HI-Z state? I've googled it intensivaly, finding the use for pul up resistors in open drain outputs though.

Thank you for your time :)

magic:
Hi-Z is for pins which can be either input or output or inactive, depending on circumstances. Think, multiple devices sharing one communication bus such that only one is allowed to drive it at a time and some/any/all of the other devices may choose to receive.

Normally you don't need pull resistors on a push/pull output, but if the output can go Hi-Z and you want the line to have a defined state, a resistor makes sense.

Jr.Maxwell:
But why would I need to put the rest of the lines in HI-Z, why not just in LOW state?

mvs:
MCU GPIOs are usually configured as Hi-Z inputs during power on and reset. It is done because it is safe for MCU, but it may not be safe for your circuit. You should use external pull up or pull down resistors to define the state in this case.

george.b:

--- Quote from: Jr.Maxwell on January 15, 2020, 09:44:47 am ---But why would I need to put the rest of the lines in HI-Z, why not just in LOW state?

--- End quote ---

That depends on what you're doing. Imagine your microcontroller is on a bus where other devices are communicating. What happens if a device tries to transmit "1", but the microcontroller is pulling a "0"?
If, instead, the microcontroller is set to tristate (hi-Z), then it won't interfere with whatever is happening on the bus.
Tristate can also be used for charlieplexing: https://en.wikipedia.org/wiki/Charlieplexing

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