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Hello, can anyone please explain me the purpose of weak pull-ups resistor of a port? What are they used for? thanx in advance, M.
On one hand, you don't want open inputs. A floating input can result in a very high current consumption.
The reason for the pull-up to be weak is that external electronics can override it, i.e. it doesn't take much current to draw the input low.
On the other hand, you can combine a weak pull-up resistor with an open-collector (or open-drain) transistor and get a pin that may be used as both input and output. If the transistor is activated, the signal may drain a lot of current, driving LEDs or other current-consuming equipment. If the transistor is deactivated, external equipment can set the pin high or low, i.e. the processor can use the pin as an input.
wow, pretty fast and clear reply. thanks for that. regards M.