Finite State Machines: VHDL Example of Detecting Sequence 1101 with Mealy and Moore Machines

1. Finite State Machines Discussion D8.1 Example 36

2. init Combinational Network s(t+1) s(t) State Register next state present state x(t) present input present output clk z(t) Canonical Sequential Network

3. init C1 C2 s(t+1) State Register next state s(t) z(t) present state x(t) present input clk Mealy Machine

4. init C2 C1 z(t) s(t+1) State Register next state s(t) present state x(t) present input clk Moore Machine

5. VHDLCanonical Sequential Network init Combinational Network s(t+1) s(t) State Register next state present state x(t) present input process(clk, init) present output clk z(t) process(present_state, x)

6. VHDLMealy Machine process(present_state, x) init C1 C2 s(t+1) State Register next state s(t) z(t) present state x(t) present input process(present_state, x) clk process(clk, init)

7. VHDLMoore Machine init C2 C1 z(t) s(t+1) State Register next state s(t) present state x(t) present input process(present_state, x) process(present_state) clk process(clk, init)

8. ExampleDetect input sequence 1101 fsm din clk dout clr din dout 1 0 1 1 0 1 1 0 1 0 0 1 1 0 1 0 0 0 0 0 0 1 0 0 1 0 0 0 0 0 1 0

9. 0 1 1 0 0 1 CLR 0 1 0 1 Use State DiagramDetect input sequence 1101 S1 0 S0 0 S11 0 S1101 1 S110 0

10. fsm.vhd fsm din clk dout clr

11. clr dout din fsm.vhd

12. clr dout din fsm.vhd

13. S1 0 0 1 1 S0 0 0 S11 0 0 CLR 1 0 1 0 S1101 1 S110 0 1 fsm.vhd

14. fsm.vhd S1 0 0 1 1 S0 0 0 S11 0 0 CLR 1 0 1 0 S1101 1 S110 0 1

15. clr dout din fsm.vhd

16. fsmx.vhd ld(0) ld(1) din fsm dout clr ld(7) btn(3) clk btn(1) bn clk_pulse btn(0) fsmx cclk mclk clkdiv

17. fsmx.vhd entity fsmx is port( mclk : in STD_LOGIC; sw : in STD_LOGIC_VECTOR(7 downto 0); btn : in STD_LOGIC_VECTOR(3 downto 0); ld : out STD_LOGIC_VECTOR(7 downto 0); a_to_g : out STD_LOGIC_VECTOR(6 downto 0); dp : out STD_LOGIC; an : out STD_LOGIC_VECTOR(3 downto 0) ); end fsmx;

18. fsmx.vhd

19. fsmx.vhd component clock_pulse port( inp : in std_logic; cclk : in std_logic; clr : in std_logic; outp : out std_logic); end component; signal clr, clk, cclk, bn: std_logic; signal clkdiv: std_logic_vector(23 downto 0);

20. fsmx.vhd bn <= btn(1) or btn(0); clr <= btn(3); U0: clk_pulse port map (inp => bn, cclk => cclk, clr =>clr, clk => clk); U1: fsm port map (clr =>clr, clk => clk, din => btn(1), dout => ld(7)); ld(0) <= BTN(0); ld(1) <= BTN(1);

21. Detect input sequence 1101Moore Machine

22. Mealy Machine Sequence DetectorDetect 1101

23. Mealy State Machine

24. -- Example 36b: Detect 1101 with Mealy machine library IEEE; use IEEE.STD_LOGIC_1164.all; entity seqdetb is port (clk: in STD_LOGIC; clr: in STD_LOGIC; din: in STD_LOGIC; dout: out STD_LOGIC); end seqdetb; architecture seqdetb of seqdetb is type state_type is (s0, s1, s2, s3); signal present_state, next_state: state_type; begin

25. sreg: process(clk, clr) begin if clr = '1' then present_state <= s0; elsif clk'event and clk = '1' then present_state <= next_state; end if; end process;

26. C1: process(present_state, din) begin case present_state is when s0 => if din = '1' then next_state <= s1; else next_state <= s0; end if; when s1 => if din = '1' then next_state <= s2; else next_state <= s0; end if; when s2 => if din = '0' then next_state <= s3; else next_state <= s2; end if; when s3 => if din = '1' then next_state <= s1; else next_state <= s0; end if; when others => null; end case; end process;

27. Seq2: process(clk, clr) begin if clr = '1' then dout <= '0'; elsif clk'event and clk = '1' then if present_state = s3 and din = '1' then dout <= '1'; else dout <= '0'; end if; end if; end process; end seqdetb; Note that dout is a registered output dout

28. Detect input sequence 1101Mealy Machine