A register in digital circuits is a memory element that is employed for storing and manipulating data. These registers are categorized based on how the information is retrieved or stored.
A serial register operates serially, accepting and transferring data one bit at a time, while a parallel register operates on a parallel fashion accepting and transferring all the bits simultaneously. Since mere transferring or storing data in digital circuits is literally achieved by shifting the bits, the registers specifically used for storing and retrieval purposes without any manipulations, are called shift registers. A shift register is generally designed with a series of flip-flops connected in the form of a chain such that the output of one is connected to the input of the other expect the output of the last one which is the actual output of the circuit. A universal shift register is one that incorporates all the features that are applicable for shifting operations including parallel input/output, left/right-shift serial inputs, operating mode control inputs (S1 & S0) and direct overriding clear line (RESET), etc.
2. Design Overview
For this assignment, a 4-bit universal shift register is designed in VHDL (VHSI Hardware Description Language) and simulated in VHDL IDE- Xilinx ISE. VHDL is generally used to write down the entire digital circuit description and its logic in the form of code or program. The circuit description is defined as entity and the logic as process. ...