VHDL Structural Architecture

1. VHDLStructural Architecture ENG2410 Week #5

2. dataflow VHDL Design Styles VHDL Design Styles behavioral (algorithmic) structural Components and interconnects Concurrent statements Sequential statements • Registers • State machines • Test benches Subset most suitable for synthesis

3. Example – 4-bit Equality Specifications: • Input: 2 vectors A(3:0) and B(3:0) • Output: One bit, E, which is 1 if A and B are bitwise equal, 0 otherwise

4. Design • Hierarchical design seems a good approach • Decompose the problem into four 1-bit comparison circuits and an additional circuit that combines the four comparison circuit outputs to obtain E. • One module/bit • Final module for E

5. Design for MX module • Logic function is • Define the output of the circuit to be: • `0’ if both inputs are similar and • `1’ if they are different? • Can implement as

6. Design for ME module • Final E is 1 only if all intermediate values are 0 • So • And a design is

7. Overall Design

8. Overall Design

9. MX Module: Data Flow ND_1 Bi_n entity mx_module is port ( Ai, Bi: in std_logic; Ei : out std_logic); end entity mx_module; architecture dataflow of mx_module is Signal Ai_n, Bi_n, ND_1, ND_2: std_logic; begin Ai_n <= not Ai; Bi_n <= not Bi; ND_1 <= Ai and B_n; ND_2 <= Bi and A_n; Ei <= ND_1 or ND_2; end architecture dataflow; Interface Ai_n ND_2 Functionality

10. ME Module: Structural entity ME_module is port ( A: in std_logic_vector(3 downto 0); B: in std_logic_vector(3 downto 0); E: out std_logic); end entity ME_module; architecture structural of ME_module is component mx_module port ( Ai, Bi: in std_logic; Ei : out std_logic); end component; Signal E0,E1,E2,E3: std_logic; begin mx0: mx_module port map (A(0), B(0), E0); mx1: mx_module port map (A(1), B(1), E1); mx2: mx_module port map (A(2), B(2), E2); mx3: mx_module port map (A(3), B(3), E3); E <= E0 nor E1 nor E2 nor E3; end architecture structural; Interface Functionality

11. Decoder: Data Flow Example: 2-to-4 decoder D3 entity dec_2_to_4 is port ( A0, A1: in std_logic; D0, D1, D2, D3: out std_logic); end entity decoder_2_to_4; architecture dataflow1 of dec_2_to_4 is Signal A0_n, A1_n: std_logic; begin A0_n <= not A0; A1_n <= not A1; D0 <= A0_n and A1_n; D1 <= A0 and A1_n; D2 <= A0_n and A1; D3 <= A0 and A1; end architecture dataflow1; A(1) D2 Interface A(0) D1 D0 A0_n A1_n Functionality

12. Structural VHDL Descriptionof 2-to-4 Line Decoder

13. Structural VHDL Description(Entity Declaration) -- 2-to-4 Line Decoder; structural VHDL Description libraryieee; use ieee.std_logic_1164.all entity decoder_2_4_w_enable is port (EN, A0, A1 : instd_logic; D0, D1, D2, D3 : outstd_logic); end decoder_2_to_4_w_enable;

14. Structural VHDL Description(Components) architecture structural1_1 of decoder_2_to_4_w_enable is component NOT1 port(in1: instd_logic; out1: outstd_logic); end component; component AND2 port(in1, in2: instd_logic; out1: outstd_logic); end component;

15. Structural VHDL Description (Signals) A0_n N0 A1_n N1 N2 N3

16. Structural VHDL Description(Connecting components) architecture structural1_1 of decoder_2_to_4_w_enable is -- component NOT1 declaration -- component NAND2 signal A0_n, A1_n, N0, N1, N2, N3: std_logic; begin g0: NOT1 port map(in1 => A0, out1 => A0_n); g1: NOT1 port map(in1 => A1, out1 => A1_n); g2: AND2 port map(in1 => A0_n, in2 => A1_n, out1 => N0); g3: AND2 port map(in1 => A0, in2 => A1_n, out1 => N1); g4: AND2 port map(in1 => A0_n, in2 => A1_n, out1 => N2); g5: AND2 port map(in1 => A0, in2 => A1, out1 => N3); g6: AND2 port map(in1 =>EN, in2 => N0, out1 => D0); g7: AND2 port map(in1 => EN, in2 => N1, out1 => D1); g8: AND2 port map(in1 => EN, in2 => N2, out1 => D2); g9: AND2 port map(in1 => EN, in2 => N3, out1 => D3); end structural_1;