The 8 inputs are translated into a series of HIGH and LOW pulses on the serial-out pin of the shift register. "Asynchronous" because the CD4021B is doing all this data collection at its own pace without coordinating with the Arduino. "Parallel" because it is all at once, like hearing a musical cord. "Input" because you are collecting information. This is called Asynchronous Parallel Input.
This means you can read the state of up to 8 digital inputs attached to the register all at once. Using a parallel to serial shift register you can collect information from 8 or more switches while only using 3 of the pins on your Arduino.Īn example of a parallel to serial register is the CD4021B, sometimes referred to as an 8-Stage Static Shift Register.
Sometimes you'll end up needing more digital input than there are pins on your Arduino.
Parallel to Serial Shifting-In with a CD4021BE Shifting In & the CD4021B
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