1. VHDL Code For Half Adder By Data Flow Modelling library ieee; use ieee.std_logic_1164.all; entity half_adder is port(a,b: in bit;s,c: out bit); end half_adder; architecture half_adder of half_adder is begin s<=(a xor b); c<=(a and b); end half_adder;
2. VHDL Code For Full Adder By Data Flow Modelling library ieee; use ieee.std_logic_1164.all; entity full_adder is port(a,b,c: in bit;sum,carry: out bit); end full_adder; architecture full_adder of full_adder is begin sum<=((a xor b) xor c); carry<=((a and b) or (b and c) or (c and a)); end full_adder;
3. (a) VHDL Code For Half Subtractor By Data Flow Modelling library ieee; use ieee.std_logic_1164.all; entity half_subtractor is port(a,b: in bit; difference,borrow: out bit); end half_subtrator; architecture half_subtractor_dfm of subtractor is begin difference<=(a xor b); borrow<=((not a) and b); end half_subtractor_dfm;
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3. (b) VHDL Code For Full Subtractor By Data Flow Modelling library ieee; use ieee.std_logic_1164.all; entity full_subtractor is port(a,b,previous_borrow: in bit; difference,next_borrow: out bit); end full_subtractor; architecture full_subtractor_dfm of full_subtractor is begin difference<=((a xor b) or (b xor previous_borrow) or (a xor previous_borrow)); next_borrow<=(((not a) and (b or previous_borrow)) or (b and previous_borrow)); end full_subtractor_dfm;
4. VHDL Code For BCD To Decimal Decoder By Data Flow Modelling library ieee; use ieee.std_logic_1164.all; entity bcd_to_decimal is port(a,b,c,d: in bit; e: out bit_vector(0 to 9)); end bcd_to_decimal; architecture bcd_to_decimal_dfm of bcd_to_decimal is begin e(0)<=((((not a) and (not b)) and (not c)) and (not d)); e(1)<=((((not a) and (not b)) and (not c)) and d); e(2)<=(((not b) and c) and (not d)); e(3)<=(((not b) and c) and d); e(4)<=((b and (not c)) and (not d)); e(5)<=((b and (not c)) and d); e(6)<=((b and c) and (not d)); e(7)<=((b and c) and d); e(8)<=(a and (not d)); e(9)<=(a and d); end bcd_to_decimal_dfm;
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5. VHDL Code For Binary to Gray Code Converter By Data Flow Modelling library ieee; use ieee.std_logic_1164.all; entity binary_to_gray is port(b0,b1,b2,b3: in bit;g0,g1,g2,g3: out bit); end binary_to_gray; architecture b_t_g of binary_to_gray is begin g3<=b3; g2<=b3 xor b2; g1<=b2 xor b1; g0<=b1 xor b0; end b_t_g;
6. VHDL Code For Gray to Binary Code Converter By Data Flow Modelling library ieee; use ieee.std_logic_1164.all; entity gray_to_binary is port(g0,g1,g2,g3: in bit;b0,b1,b2,b3: out bit); end gray_to_binary; architecture g_t_b of gray_to_binary is begin b3<=g3; b2<=g3 xor g2; b1<=(g3 xor (g2 xor g1)); b0<=(g3 xor (g2 xor (g1 xor g0))); end;
7. VHDL Code For BCD To Excess3 Code Converter By Data Flow Modelling library ieee; use ieee.std_logic_1164.all; entity bcd_to_excess_3 is port(b0,b1,b2,b3: in bit; e0,e1,e2,e3: out bit); end bcd_to_excess_3; architecture bcd_to_excess_3_dfm of bcd_to_excess_3 is begin e3<=((b3 or (b2 and b0)) or (b2 and b1)); e2<=(((not b2) and b0) or ((not b0) and (b1 xor b2))); e1<=(b1 xnor b0); e0<=(not b0); end bcd_to_excess_3_dfm; Page 3 of 14
8. (a) VHDL Code For 4×1 Multiplexer Using IF-ELSE Statements library ieee; use ieee.std_logic_1164.all; entity mux_4_1 is port(s: in bit_vector(0 to 1); d: in bit_vector(0 to 3); y: out bit); end mux_4_1; architecture mux_4_1_behavioural_if_else of mux_4_1 is begin process(s,d) begin if s="00" then y<=d(0); elsif s="01" then y<=d(1); elsif s="10" then y<=d(2); else y<=d(3); end if; end process; end mux_4_1_behavioural_if_else;
8. (b) VHDL Code For 4×1 Multiplexer Using CASE Statements library ieee; use ieee.std_logic_1164.all; entity mux_4_1 is port(s: in bit_vector(0 to 1); d: in bit_vector(0 to 3); y: out bit); end mux_4_1; architecture mux_4_1_behavioural_case of mux_4_1 is begin process(s,d) begin case s is when "00" => y<=d(0); when "01" => y<=d(1); when "10" => y<=d(2); when others => y<=d(3); end case; end process; end mux_4_1_behavioural_case;
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9. VHDL Code For 2×4 Decoder By Data Flow Modelling library ieee; use ieee.std_logic_1164.all; entity decoder_2_4 is port(a,b,e: in bit; d0,d1,d2,d3: out bit); end decoder_2_4; architecture decoder_2_4_dfm of decoder_2_4 is begin d0<= (((not a) and (not b)) and e); d1<= (((not a) and b) and e); d2<= ((a and (not b)) and e); d3<= ((a and b) and e); end decoder_2_4_dfm;
10.
VHDL Code For 2 Bit Multiplier By Data Flow Modelling
library ieee; use ieee.std_logic_1164.all; entity multiplier_2_bit is port(a: in bit_vector(1 downto 0);b: in bit_vector(1 downto 0); d: out bit_vector(3 downto 0)); end multiplier_2_bit; architecture multiplier_2_bit_dfm of multiplier_2_bit is signal c: bit; begin d(0)<=(a(0) and b(0)); d(1)<=((a(1) and b(0)) xor (a(0) and b(1))); c<=((a(1) and b(0)) and (a(0) and b(1))); d(2)<=((a(1) and b(1)) xor c); d(3)<=((a(1) and b(1)) and c); end multiplier_2_bit_dfm;
11.
VHDL Code For 2 Bit Comparator By Data Flow Modelling
library ieee; use ieee.std_logic_1164.all; entity comparator_2_bit is port(a,b: in bit_vector(1 downto 0); y: out bit_vector(2 downto 0)); end comparator_2_bit; architecture comparator_2_bit_dfm of comparator_2_bit is begin y(0)<= (((a(1) and (not b(1))) or (a(1) and a(0) and (not b(0)))) or ((not b(1)) and a(0) and (not b(0)))); y(1)<= ((((not a(1)) and b(1)) or ((not a(1)) and (not a(0)) and b(0))) or (b(1) and (not a(0)) and a(0))); y(2)<= ((a(1) xnor b(1)) and (a(0) xnor b(0))); end comparator_2_bit_dfm; Page 5 of 14
12.
VHDL Code For Half Adder by Structural Modelling
library ieee; use ieee.std_logic_1164.all; entity half_adder is port(a,b: in bit; sum,carry: out bit); end half_adder; architecture half_adder_struct of half_adder is component xor1 is port(p,q: in bit; r: out bit); end component; component and1 is port(u,v: in bit; w: out bit); end component; begin x1:xor1 port map(a,b,sum); x2:and1 port map(a,b,carry); end half_adder_struct; entity xor1 is port(p,q: in bit; r: out bit); end xor1; architecture xor_1_dfm of xor1 is begin r<=p xor q; end xor_1; entity and1 is port(u,v: in bit; w: out bit); end and1; architecture and_1_dfm of and1 is begin w<=u and v; end and_1;
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13.
VHDL Code For 4-bit Parallel Adder by Structural Modelling
library ieee; use ieee.std_logic_1164.all; entity full_adder_4_bit is port(a,b: in bit_vector(3 downto 0); carry_in: in bit; sum: out bit_vector(3 downto 0); carry_out: out bit); end; architecture structural_4_bit_full_adder of full_adder_4_bit is component full_adder port(x,y,zin: in bit; s,c: out bit); end component; signal carry: bit_vector(4 downto 0); begin carry(0)<=carry_in; GK:for i in 3 downto 0 generate FA:full_adder port map(a(i),b(i),carry(i),sum(i),carry(i+1)); end generate GK; carry_out<=carry(4); end; entity full_adder is port(p,q,r:in bit; u,v:out bit); end; architecture data_flow_full_adder of full_adder is begin u<=((p xor q) xor r); v<=((p and q) or (q and r) or (r and p)); end;
14.
VHDL Code For 4-Bit Parallel Subtractor by Structural Modelling
library ieee; use ieee.std_logic_1164.all; entity full_subtractor_4_bit is port(a,b: in bit_vector(3 downto 0); borrow_in: in bit; difference: out bit_vector(3 downto 0); borrow_out: out bit); end full_subtractor_4_bit; architecture full_subtractor_4_bit_struct of full_subtractor_4_bit is component full_subtractor is port(x,y,zin: in bit; diff,zout: out bit); end component; signal borrow: bit_vector(4 downto 0); begin borrow(0)<=borrow_in; GK: for i in 3 downto 0 generate FS: full_subtractor port map(a(i),b(i),borrow(i),difference(i),borrow(i+1)); Page 7 of 14
end generate GK; borrow_out<=borrow(4); end full_subtractor_4_bit_struct; entity full_subtractor is port(r,s,t: in bit; u,v: out bit); end full_subtractor; architecture full_subtractor_dfm of full_subtractor is begin u<=((r xor s) xor t); v<=(((not r) and t) or ((s and t) or ((not r) and s))); end full_subtractor_dfm;
15.
VHDL Code For 4×1 Multiplier By Data Flow Modelling
library ieee; use ieee.std_logic_1164.all; entity mux_4_1 is port(s: in bit_vector(1 downto 0);d: in bit_vector(3 downto 0); y: out bit); end; architecture mux_4_1_dfm of mux_4_1 is begin y<=d(0) when s="00" else d(1) when s="01" else d(2) when s="10" else d(3); end;
16.
VHDL Code For 2×4 Decoder By Behavioral Modelling
library ieee; use ieee.std_logic_1164.all; entity decoder_2_4 is port(a: in bit_vector(0 to 1); d: out bit_vector(0 to 3)); end decoder_2_4; architecture decoder_2_4_behavioural of decoder_2_4 is begin process(a) begin if a="00" then d<="0001"; elsif a="01" then d<="0010"; elsif a="10" then Page 8 of 14
d<="0100"; else d<="1000"; end if; end process; end decoder_2_4_behavioural;
17. (a)VHDL Code For JK Flip Flop(Asynchronous) By Behavioral Modelling library ieee; use ieee.std_logic_1164.all; entity J_K_flip_flop is port(J,K,reset,clock: in bit; q: inout bit; qbar: out bit); end J_K_flip_flop; architecture asynchronous_reset_J_K_flip_flop_behavioural of J_K_flip_flop is begin process(clock,reset) begin if reset='1' then q<='0'; elsif clock='1' and clock'event then q<=((J and (not q)) or ((not K) and q)); end if; end process; end asynchronous_reset_J_K_flip_flop_behavioural;
17. (b) VHDL Code For JK Flip Flop(Synchronous) By Behavioral Modelling library ieee; use ieee.std_logic_1164.all; entity J_K_flip_flop is port(J,K,clock,reset: in bit; q: inout bit; qbar: out bit); end J_K_flip_flop; architecture synchronous_reset_J_K_flip_flop_behavioural of J_K_flip_flop is begin process(clock) begin if clock='0' and clock'event then if reset='1' then q<='0'; else q<=(((J and (not q)) or ((not K) and q)); end if; end if; end process; qbar<=(not q); end synchronous_reset_J_K_flip_flop_behavioural; Page 9 of 14
18. (a)VHDL Code For D Flip Flop(Asynchronous) By Behavioral Modelling library ieee; use ieee.std_logic_1164.all; entity D_flip_flop is port(d,clock,reset: in bit; q: inout bit; qbar: out bit); end D_flip_flop; architecture asynchronous_reset_D_flip_flop_behavioural of D_flip_flop is begin process(clock,reset) begin if reset='1' then q<='0'; elsif clock='0' and clock'event then q<=d; end if; end process; qbar<=(not q); end asynchronous_reset_D_flip_flop_behavioural;
18.(b)VHDL Code For D Flip Flop(Synchronous) By Behavioral Modelling library ieee; use ieee.std_logic_1164.all; entity D_flip_flop is port(d,clock,reset: in bit; q: inout bit; qbar: out bit); end D_flip_flop; architecture synchronous_reset_D_flip_flop_behavioural of D_flip_flop is begin process(clock) begin if clock='0' and clock'event then if reset='1' then q<='0'; else q<=d; end if; end if; end process; qbar<=(not q); end synchronous_reset_D_flip_flop_behavioural;
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19. (a) VHDL Code For T Flip Flop(Asynchronous) By Behavioral Modelling library ieee; use ieee.std_logic_1164.all; entity T_flip_flop is port(T,reset,clock: in bit; q: inout bit; qbar: out bit); end T_flip_flop; architecture asynchronous_reset_T_flip_flop_behavioural of T_flip_flop is begin process(clock,reset) begin if reset='1' then q<='0'; elsif clock='1' and clock'event then q<=((T and (not q)) or ((not T) and q)); end if; end process; end asynchronous_reset_T_flip_flop_behavioural;
19.(b) VHDL Code For T Flip Flop(Synchronous) By Behavioral Modelling library ieee; use ieee.std_logic_1164.all; entity T_flip_flop is port(T,clock,reset: in bit; q: inout bit; qbar: out bit); end T_flip_flop; architecture synchronous_reset_T_flip_flop_behavioural of T_flip_flop is begin process(clock) begin if clock='0' and clock'event then if reset='1' then q<='0'; else q<=(((T and (not q)) or ((not T) and q))); end if; end if; end process; qbar<=(not q); end synchronous_reset_T_flip_flop_behavioural;
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20. VHDL Code For 3 Bit Counter By Behavioral Modeling library ieee; use ieee.numeric_std.all; use ieee.std_logic_1164.all; use ieee.std_logic_unsigned.all; entity counter_3_bit is port(clock,reset: in bit; z: out unsigned(0 to 2)); end counter_3_bit; architecture counter_3_bit_behavioural of counter_3_bit is begin process(clock,reset) variable temp: unsigned(0 to 2):=(others=>'0'); begin if reset='1' then temp:=(others=>'0'); elsif clock='0' and clock'event then temp:=temp+1; end if; z<=temp; end process; end counter_3_bit_behavioural;
21. VHDL Code For Shift Register By Behavioral Modelling library ieee; use ieee.std_logic_1164.all; entity shift_register is port(clock,serial_input: in bit; serial_output: out bit); end shift_register; architecture shift_right_register_8_bit_behavioural of shift_register is signal temp: bit_vector(7 downto 0); begin process(clock) begin if clock='1' and clock'event then serial_output<=temp(0); for i in 7 downto 1 loop temp(i-1)<=temp(i); end loop; temp(7)<=serial_input; end if; serial_output<=temp(7); end process; end shift_right_register_8_bit_behavioural;
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22. (a) VHDL Code For State Machine Modeling (Mealey) By Behavioral Modeling. library ieee; use ieee.std_logic_1164.all; entity mealy_fsm is port(a,clock: in bit; z: out std_logic); end mealy_fsm; architecture mealy_fsm_behavioural of mealy_fsm is type mealy_type is(st0,st1,st2,st3); signal p_state,n_state: mealy_type; begin seq_part: process(clock) begin if clock='0' then p_state<=n_state; end if; end process seq_part; comb_part:process(p_state,a) begin case p_state is when st0 => if a='1' then z<='1'; n_state<=st3; else z<='0'; end if; when st1 => if a='1' then z<='0'; n_state<=st0; else z<='1'; end if; when st2 => if a='0' then z<='0'; else z<='1'; n_state<=st1; end if; when st3 => z<='0'; if a='0' then n_state<=st2; else n_state<=st1; Page 13 of 14
end if; end case; end process comb_part; end mealy_fsm_behavioural;
23. (b) VHDL Code For State Machine Modeling (Moorey) By Behavioral Modeling. library ieee; use ieee.std_logic_1164.all; entity moore_fsm is port(a,clock: in bit; z: out std_logic); end moore_fsm; architecture moore_fsm_behavioural of moore_fsm is type state_type is(st0,st1,st2,st3); signal moore_state: state_type; begin process(clock) begin if clock='0' then case moore_state is when st0 => z<='1'; if a='1' then moore_state<=st2; end if; when st1 => z<='0'; if a='1' then moore_state<=st3; end if; when st2 => z<='0'; if a='0' then moore_state<=st1; else moore_state<=st3; end if; when st3 => z<='1'; if a='1' then moore_state<=st0; end if; end case; end if; end process; end moore_fsm_behavioural;
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