shiftregister

A shift register is a type of storage register in which the binary data can be shifted from one location to another within the register by clock pulses. It consists of multiple flip-flops connected in series so that the output of one stage feeds the input of the next. On each clock edge, the bit in each stage moves to the adjacent stage, enabling data to flow through the chain in a controlled, serial fashion.

Shift registers support several configurations. Serial-in/serial-out (SISO) transfers data one bit at a time through the entire chain. Serial-in/parallel-out (SIPO) loads data serially and presents it in parallel form. Parallel-in/serial-out (PISO) accepts a full word in parallel and outputs it serially. Parallel-in/parallel-out (PIPO) holds and presents a word in parallel. In synchronous shift registers all stages respond to a common clock, while asynchronous (or ripple) variants shift data with stage-to-stage timing delays.

Typical implementations use edge-triggered D flip-flops and come in various forms, including small integrated circuits such as 8-bit devices. Examples include serial-in, parallel-out types with a latch for output stabilization, and parallel-in, serial-out types for serial data extraction. Real-world devices often add features such as tri-state outputs or built-in latches to separate shifting from data presentation.

Applications of shift registers include temporary data storage and delay lines, data format conversion between serial and parallel forms, and expanding I/O capability in microcontrollers and processors. They are central to serializing and deserializing data in communications, buffering in digital systems, and implementing simple data repetition or routing schemes, while offering a low-pin-count alternative to larger memory elements for certain tasks.