In digital circuits, a shift register is a device that allows other inputs or outputs to be added to the microcontroller. It is achieved by converting data between parallel and serial formats. Connect several flip-flops in series to form a shift register. The microprocessor uses serial information to communicate with the shift register, and the shift register collects or outputs information in a parallel (multi-pin) format. Data is input to the device in parallel or serial mode, and then each time pulse moves one bit to the left or right in turn and outputs it at the output. The shift register can register data and shift the data in it to the left or right in turn under the action of a clock signal. There are many shift registers, including left shift registers, right shift registers, bidirectional shift registers, and circular shift registers.