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# GPIO concepts
Notes on GPIO concepts
## Introduction
* MCUs have PORTS and PINS , PORTS are a collection of PINS and each PIN has a functionality thats assigned by the manufacturer
* GPIO is used as switch , interrupts , in SPI as CS etc
* GPIO - General Purpose Input Output has the below structure
## Input Confiiguration:
* PIN of an MCU can be configured as Input with pullup or pulldown resistors
* Why pullup or pulldown ? Because if a PIN doesnt have a internal pullup or extenal pullup/down activated then it will be in floating state when nothing is connected and this will lead to wrong input read values
* floating state can also cause leakage current (the mosfets will turn on partially and the current will leak)
## Output Configuration:
* Output PIN can be in open drain (pulled low when 0 but floating when 1) so it requires an external pullup resistor (use this when the current to be sourced needs to be higher than what mosfet / PIN can source)
* Output PIN can be in Push pull configuration and this doesnt require a pullup resistor
