external pullup resistor for microcontroller

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how to enable and disable external pullup resistor to microcontroller pin because i'm using one port pin for two applications.. For one application need external pullup resistor whereas for the other application pullup not required.
 

Hi,

Swiching an external pullup is the same as high side switching any other load.

Simple: use a P FET. Source to VCC, drain to the high side of the pullup.
Gate is the low active enable signal.

Klaus
 

If the second application is also digital (I/O, PWM, etc.), then there's no need to remove it. You might need to make it a "weak" pull-up if the alternate function is an output.
 

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