Shift Register - Types - Functions - Leo Tutorials.

Shift Register : 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 cascade, with the output of one flip flop connected to the input receive common clock pulse that initiate the shift from one stage to the next.
          The simplest possible shift register is one that uses only flip-flops. 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 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 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.

Types of Shift Register : Shift register are as following ;

  1. Unidirectional Shift Register : A register capable of shifting in one direction only is called a unidirectional shift register.
  2. Bidirectional Shift Register : A register that can shift in both direction is called a bi-directional shift register.
              Some shift registers provide the necessary input and output terminal for parallel transfer.

              Shift registers are often used to interface digital systems situated remotely from each other. For example, suppose that it is necessary to transmit an n-bit quantity between two points. If the distance between the source and the destination is too far, it will be expensive to use n lines to transmit the n-bits in parallel. It may be more economical to use at a time. the transmitter loads the n-bit data in parallel into a shift register and then transmits the data from the serial output line. The receiver accepts that data serially into a shift register through its serial inputs line.
              Shift registers can be built using D, J-K ore S-R flip flops. Depending upon the modes of loading and reading out the data there are four types of shift registers :
  • Serial-in, Serial-out,
  • Serial-in, parallel-out,
  • Parallel-in, serial-out,
  • Parallel-in, parallel-out.
     Functions of a Shift register : The most general shift register has all the characteristics listed below:

  1. An input for clock pulses to synchronize all operations. 
  2. A shift-right operation and a serial input line associated with the shift-right
  3. A shift-left operation and a serial input lines associated with the shift-left
  4. A parallel load operation and n input lines associated with the parallel transfer.
  5. n parallel output lines.
  6. A control state that leaves the information is the register unchanged even though clock pulses are applied continuously

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