4-bit shift register using d flip flop
A register capable of shifting its binary information in one or both directions is called a shift register. The logical configuration of a shift register consists of a chain of flip-flops in a cascade, with the output of one flip-flop connected to the input of the next flip-flop. All flip-flops receive common clock pulses that initiate the shift from one stage to the next. The simplest possible shift register is one that uses only flip-flops, as shown below:
4-bit shift register:
The output of a given flip-flop is connected to the D input of the flip-flop at its right. The clock is common to all flip-flops. The serial input determines what goes into the leftmost position during the shift. The serial output is taken from the output of the rightmost flip-flop.
Sometimes it is necessary to control the shift so that it occurs with certain clock pulses but not with others. This can be done by inhibiting the clock from the input of the register if we do not want it to shift. When the shift register is used, the shift can be controlled by connecting the clock to the input of an AND gate, and a second input of the AND gate can then control the shift by inhibiting the clock. However, it is also possible to provide extra circuits to control the shift operation through the D inputs of the flip-flops rather than the clock input.