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Why Pull UP Resistors In MUX control lines ?

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ranaya

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Hello all......

Can any 1 explain me what is the importance of using pull up resistors in multiplexer control lines ?? In many circuits I have seen this, :

ddw.JPG

Current flows from vcc to digital pin of MCU.
 

FvM

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Can any 1 explain me
Not without knowing what's on the left side. Pull-up makes sense e.g. for 8051 port0, which has open drain outputs. In other cases, it may be waste of components and energy, respectively brainless copy-and-paste.
 

demetal

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The pull-up resistor ensures that the wire is at a defined logic level even if no active devices are connected to it... It helps to maintain a logic state even if the input to the mux is disconnected suddenly and avoids error outputs... It actually maintains a state of logic High when input is inactive and an activeness of input will override the logic High state...
 

Tahmid

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The pull-up resistors shouldn't be necessary if the microcontroller outputs are always either driven high or low.

However the pull-up resistors may be used to ensure that there is a logic level present at all times as demetal has said. This could be, as FvM has said, if the outputs are open-drain, or if they have mistakenly been configured as inputs or if the outputs are high-impedance tri-state, eg when the microcontroller is reset, etc.

Hope this helps.
Tahmid.
 

nikhildascl

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But how the data's are differentiated? What will be the voltage at the pin if the data is logic high or logic low?
 

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