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, SPI bus, or SerDes. External reset Switch debounce Input pull-up (or -down) resistors open collector output Pulse counting Timing pulses Some kinds of special I/O functions can sometimes be emulated with general-purpose input/output and bit banging software.
See also Atari SIO
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