Editing Shift register (section)

=== More I/O pins ===
Shift registers are commonly attached to [[microcontrollers]] when more [[general-purpose input/output]] pins are required than are available, sometimes over a [[Serial Peripheral Interface#Daisy chain configuration|Serial Peripheral Interface in daisy chain configuration]], which allows any number of binary devices to be accessed using only two to four pins, though more slowly than parallel I/O.

For more outputs, SIPO shift registers are used. The parallel outputs of the shift register and the desired state for all those devices can be sent out of the microcontroller using a single serial connection.

For more inputs, PISO shift registers are used. Each binary input (such as a [[Push-button|button]] or more complicated circuitry) is attached to a parallel input of the shift register, then the data is sent back serially to the microcontroller.