1. ASIC 121: Practical VHDL Digital Design for FPGAs Tutorial 2 October 4, 2006

2. Contributions I have taken some of the slides in this tutorial from Jeff Wentworth’s ASIC 120

3. Combination vs Sequential Combinational Logic –Output only depends on input –Examples: AND, OR, MUX Sequential Logic –Output depends on inputs and memory –Examples: State Machine, Counter

4. Memory Two popular ways of implementing memory: –Synchronous memory (most popular) Uses Flip Flops with a Clock signal –Asynchronous memory Uses Latches Much more difficult to design with

5. Basic Feedback Element: SR latch SRQQ next 0000 0011 0100 0110 1001 1011 110N/A 111

6. D Flip-Flop or Register DClkQQ next 0000 0011 1000 1011 0 0101 00 0 0101 10 1 0101 01 1 0101 11

7. ASIC 120 Read through the ASIC 120 Tutorial 2 Gives a good explanation of state machines and basic VHDL

8. Independent Tasks All students should have evaluation copies of Modelsim and Quartus II, if not see Tutorial 1

9. Quartus II Exercise This exercise builds on the one performed in Tutorial 1 Open Quartus II, Select File->New Project Wizard, Select a valid working directory (should be an empty folder) Name the project and entity “full_adder” Click next for all other menus Select File->New. Select VHDL File

10. Quartus II Exercise Cont Save the file as full_adder.vhd, with the contents: library ieee; use ieee.std_logic_1164.all; entity full_adder is Port ( i_X, i_Y, i_Cin: in STD_LOGIC; o_FA_Sum, o_FA_Cout : out STD_LOGIC ); end full_adder; architecture main of full_adder is Component half_adder Port ( i_A, i_B: in STD_LOGIC; o_Sum, o_Carry: out STD_LOGIC ); end Component; signal carry_1, carry_2, sum_1: STD_LOGIC;

11. Quartus II Exercise Cont begin adder1 : half_adder Port map( i_A => i_X, i_B => i_Y, o_Sum => sum_1, o_Carry => carry_1); adder2 : half_adder Port map( i_A => i_Cin, i_B => sum_1, o_Sum => o_FA_Sum, o_Carry => carry_2); o_FA_Cout <= carry_1 or carry_2; end main;

12. Quartus II Exercise Cont Go to Project->Add Files and add the half_adder.vhd file from Tutorial 1 You have now seen a hierarchical VHDL design with multiple files

13. Quartus II Exercise Cont Select Processing->Start->Analysis and Synthesis Make sure it completes successfully Next Step –Read through the help file under “simulation” –Try Simulating the design

14. Exercise 2 Full adders can be chained together into something called a “ripple adder” 3 bit adder (A + B = S): Full Adder A0A1A2B0B1B2 Carry In Carry Out S0S1S2

15. Exercise 2 Cont’d Create the architecture description for a 4 bit ripple adder to implement the entity: library ieee; use ieee.std_logic_1164.all; entity ripple_adder is port ( A : in std_logic_vector(3 downto 0); B : in std_logic_vector(3 downto 0); c_in : in std_logic; sum : out std_logic_vector(3 downto 0); c_out : out std_logic ); end ripple_adder;

16. VHDL DFF (Flip Flop) library ieee; use ieee.std_logic_1164.all; entity DFF is port ( d, clk : in STD_LOGIC; q : out STD_LOGIC ); end DFF; architecture main of DFF is begin process (clk) begin if (clk'event and clk = '1') then q <= d; end if; end process; end main;