Question

1 Simulations to verify a 4-bit Register Simulate and verify a 4-bit Register using behavioral VHDL code in ModelSim. Recall that sequential circuits depend on both present and past state. Sequential circuits are in contrast to combinational circuits, which depend on input values from only the present state. Fur- thermore, recall that a flip-flop is a fundamental circuit used to create more complex sequential circuits. A register is an array of storage components, such as flip-flops. For example, a 4-bit register consists of 4 flip-flops and is able to store 4 bits of information (state). In this section, you will generate a 4-bit register. The first objective is to observe the behavior of the 4-bit register. In Figures la and 1b, the schematic of the 4-bit register is shown. In Figure 1d, a state table for the register is shown. Hint: To get started, implement the 4-bit register as behavioral VHDL code (VHDL Code 1) and verify it. Remember to utilize the clock function in ModelSim for faster testing.

Answer 1

entity register is

port (clk, en: in std_logic;

D: in std_logic_vector(3 down to 0)

Q: out std_logic_vector(3 down to 0));

end register

architecture behavioral of register is

begin

process(D,clk)

begin

if(en='0')

Q<=0000;

endif

else

Q<= D;

endprocess;

end behavioral

In the above program

D is input of 4 bit and Q is output Here we used En has 'enable' pin if enable is 0 then Q will be assigned as 0000 else q will be assigned by D