The implemented LFSR uses a one-to-many structure, rather than a many-to-one structure, since this structure always has the shortest clock-to-clock delay path.Ī diagram of an eight bit LFSR is as follows:
The choice of taps determines how many values there are in a given sequence before the sequence repeats. It is this feedback that causes the register to loop through repetitive sequences of pseudo-random value. Register bits that do not need an input tap, operate as a standard shift register. This is a PDF file.įeedback around an LFSR's shift register comes from a selection of points (taps) in the register chain and constitutes XORing these taps to provide tap(s) back into the register. Linear feedback shift registers have multiple uses in digital systems design.Ī design modeled after LFSRs often has both speed and area advantages over a functionally equivialent design that does not use LFSRs.Īn explanation of how to use LFSRs for these applications can be found in the sales primer for a Linear Feedback Shift Register Megafunction sold by Altera. A Linear Feedback Shift Register is a sequential shift register with combinational logic that causes it to pseudo-randomly cycle through a sequence of binary valuesĪ Linear Feedback Shift Register is a sequential shift register with combinational logic that causes it to pseudo-randomly cycle through a sequence of binary values.
