2. 1 VLSI DESIGN USING VHDL Part II A workshop by Dr. Junaid Ahmed Zubairi

3. 2 Workshop Outline  Introduction to the workshop and setting targets  Combinational and sequential logic  Max+plusII package features and usage guide  Hands on VHDL (Lab1)  VHDL design units  Designing a simple circuit and its testing (Lab2)  Design of a sequential logic circuit (lab3)  Design project

4. 3 Some Example Designs  A multiplexer is a circuit that has several inputs and only one output line  One of the inputs is selected using selection lines for onward connection with the output  In VHDL, multiplexers can be achieved using conditional assignment statements

5. 4 A 4-to-1 Multiplexer  library ieee;  use ieee.std_logic_1164.all;  entity mux4to1 is  port (Sel:in std_logic_vector(0 to 1);  A:in std_logic_vector(0 to 3); Y:out std_logic);  end mux4to1;  architecture mux1 of mux4to1 is  begin  Y <= A(0) when Sel = ’00’ else  A(1) when Sel = ’01’ else  A(2) when Sel = ’10’ else  A(3) when others;  end mux1;

6. 5 An 8-Bit Register With Asynchronous Reset  library ieee;  use ieee.std_logic_1164.all;  entity reg8 is  port (D:in std_logic_vector(7 downto 0);  reset,clk:in std_logic; Q:out std_logic_vector(7 downto 0));  end reg8;  architecture myreg of reg8 is  begin  process(reset,clk)  begin  if reset= '0' then Q<= "00000000";  elsif clk'event and clk='1' then Q<=D;  end if;  end process;  end myreg;

7. 6 Generate Statements  You can generate several components using for..generate statements in VHDL  For example, derive a 16-to-1 Multiplexer from the given 4-to-1 Multiplexer  The source code is given

8. 7 Generate Statements  library ieee;  use ieee.std_logic_1164.all;  entity mux16to1 is  port (Sel:in std_logic_vector(0 to 3);  A:in std_logic_vector(0 to 15); Y:out std_logic);  end mux16to1;  architecture mux2 of mux16to1 is  Begin  Signal m:std_logic_vector(0 to 3);  Component mux4to1 is  Port (Sel:in std_logic_vector(0 to 1);  A:in std_logic_vector(0 to 3); Y:out std_logic);  end component;

9. 8 Generate Statement  Begin  G1: for I in 0 to 3 generate  Muxes: mux4to1 port map (Sel(0 to 1), A(4*i to 4*i+3), m(i));  End generate;  Mux5: mux4to1 port map (Sel(2 to 3), m(0 to 3), Y);  End structure;

10. 9 Design Project  Using the 4-bit comparator designed earlier, develop a circuit that contains a comparator and a 4-bit register. The register will be loaded with a 4-bit number with the rising edge of the clock. Another four bit number will be applied directly to the other input of the comparator. Show the results