- SISO Shift Register Definition: A Serial In Serial Out (SISO) shift register is defined as a type of shift register where data is loaded and retrieved in serial mode.
- Right-Shift Operation: In a right-shift SISO shift register, data bits move towards the right with each clock pulse.
- Left-Shift Operation: A left-shift SISO shift register works similarly but moves data bits from right to left.
- Working Principle: The working principle of SISO shift registers involves data entering bit-by-bit and moving through flip-flops with each clock pulse.
- Initial Setup: All flip-flops are cleared initially, and input data is fed serially to the first flip-flop.
Serial In Serial Out (SISO) shift registers are a kind of shift registers where both data loading as well as data retrieval to/from the shift register occurs in serial-mode. Figure 1 shows a n-bit synchronous SISO shift register sensitive to positive edge of the clock pulse. Here the data word which is to be stored is fed bit-by-bit at the input of the first flip-flop. Further it is seen that the inputs of all other flip-flops (except the first flip-flop FF1) are driven by the outputs of the preceding ones say for example, the input of FF2 is driven by the output of FF1. At last the data stored within the register is obtained at the output pin of the nth flip-flop in serial-fashion.
Initially, all the flip-flops are cleared by applying a high signal to their clear pins. Then, the input data word is fed serially into FF1.
This causes the bit appearing at the D1 pin (B1) to be stored into FF1 as soon as the first leading edge of the clock appears. Further at the second clock tick, B1 gets stored into FF2 while a new bit enters into FF1 (B2).
With each rising clock pulse, the data bits continue to shift. This means that with every clock pulse, the data in the register moves one bit to the right. The design in Figure 1 is a right-shift SISO shift register. The first bit of an input word appears at the output of the nth flip-flop on the nth clock tick. Further clock cycles produce the successive bits of the input data word as serial output (Table I). Figure 2 shows the corresponding waveforms.
Similar to the right-shift SISO shift register, there is also a left-shift SISO shift register (Figure 3). However, the working principle remains the same, except that data moves from right to left.
