Special input/output

{{Short description|Specialised microcontroller functionality}}

Special input/output (Special I/O or SIO) are inputs and/or outputs of a microcontroller designated to perform specialized functions or have specialized features.

Specialized functions can include:

• Hardware interrupts,
• analog input or output
• PWM output
• Serial communication, such as UART, USART,{{cite book |url=https://books.google.com/books?id=NPSQShtCQaUC&pg=PA357 |page=357 |title=Advanced PIC Microcontroller Projects in C |author=Dogan Ibrahim |year=2011 |isbn=9780080558424 |publisher=Elsevier Science}}{{cite journal |url=https://www.researchgate.net/publication/337440463 |last=Adetoyi |first=O.E. |year=2017 |title=Development of Smart Card Door Access Control System |journal=International Journal of Electronics Communication and Computer Engineering |volume=8 |issue=1 |pages=41–44}} SPI bus, or SerDes.
• External reset
• Switch debounce
• Input pull-up (or -down) resistors
• open collector output
• Pulse counting{{cite book |url=https://books.google.com/books?id=5rntCAAAQBAJ&pg=PA61 |page=61 |title=Embedded Robotics; Mobile Robot Design and Applications with Embedded Systems |author=Thomas Bräunl |year=2013 |isbn=9783662050996 |publisher=Springer Berlin Heidelberg}}
• Timing pulses{{cite book |url=https://books.google.com/books?id=TbldAQAAQBAJ&pg=PA265 |page=265 |title=Arduino Microcontroller Processing for Everyone! |author=Steven F. Barrett |year=2013 |isbn=9781627052542 |publisher=Morgan & Claypool Publishers}}{{cite journal |url=https://www.epj-conferences.org/articles/epjconf/pdf/2017/14/epjconf-isvhecri2016_19002.pdf |last1=Shepetov |first1=A. |last2=Chubenko |first2=A. |last3=Kryakunova |first3=O. |last4=Nikolayevsky |first4=N. |last5=Salikhov |first5=N. |last6=Yanke |first6=V. |year=2017 |title=The STM32 microcontroller based pulse intensity registration system for the neutron monitor |journal=EPJ Web of Conferences |volume=145 |page=19002 |publisher=EDP Sciences|doi=10.1051/epjconf/201714519002 |arxiv=1712.00713 |bibcode=2017EPJWC.14519002S }}

Some kinds of special I/O functions can sometimes be emulated with general-purpose input/output and bit banging software.