ELECTRONICS AND COMMUNICATION ENGG DEPT.

GOVERNMENT ENGINEERING COLLEGE, SECTOR -28, GANDHINAGAR-302028

MINI PROJECT

AIM : IMPLEMENTATION OF Mealy FSM (Finite State

Machine) USING VHDL.

Description: A finite-state machine (FSM) is conceived as an abstract machine that can be in one of

a finite number of states. The machine is in only one state at a time;

The state it is in at any given time is called the current state. It can change from one state

to another when initiated by a triggering event or condition, this is called a transition.

Mealy FSM uses only input actions, i.e., output depends on input and state. The use of a

Mealy FSM leads often to a reduction of the number of states.

Mealy FSM Logic

VLSI TECHNOLOGY AND DESIGN Subject Code: 161004

ELECTRONICS AND COMMUNICATION ENGG DEPT.

GOVERNMENT ENGINEERING COLLEGE, SECTOR -28, GANDHINAGAR-302028

sThe next state and output of an FSM is a function of the input and of the current state. 

VHDL Code:

library ieee; use IEEE.std_logic_1164.all;

entity fsm is port (clk : in std_logic; reset : in std_logic; input : in std_logic; output : out std_logic ); end fsm;

architecture behavioral of fsm is

type state_type is (s0,s1,s2,s3); signal current_s,next_s: state_type;

begin

process (clk,reset) begin if (reset='1') then current_s <= s0; elsif (rising_edge(clk)) then current_s <= next_s; end if; end process;

process (current_s,input) begin case current_s is

VLSI TECHNOLOGY AND DESIGN Subject Code: 161004

ELECTRONICS AND COMMUNICATION ENGG DEPT.

GOVERNMENT ENGINEERING COLLEGE, SECTOR -28, GANDHINAGAR-302028

when s0 => if(input ='0') then output <= '0'; next_s <= s1; else output <= '1'; next_s <= s2; end if;

when s1 => if(input ='0') then output <= '0'; next_s <= s3; else output <= '0'; next_s <= s1; end if;

when s2 => if(input ='0') then output <= '1'; next_s <= s2; else output <= '0'; next_s <= s3; end if;

when s3 => if(input ='0') then output <= '1'; next_s <= s3; else output <= '1'; next_s <= s0; end if; end case; end process;

end behavioral;

VLSI TECHNOLOGY AND DESIGN Subject Code: 161004

ELECTRONICS AND COMMUNICATION ENGG DEPT.

GOVERNMENT ENGINEERING COLLEGE, SECTOR -28, GANDHINAGAR-302028

RTL View:

Simulation Result:

VLSI TECHNOLOGY AND DESIGN Subject Code: 161004

ELECTRONICS AND COMMUNICATION ENGG DEPT.

GOVERNMENT ENGINEERING COLLEGE, SECTOR -28, GANDHINAGAR-302028

Conclusion:

This way we can design & implement mealy FSM in VHDL.

VLSI TECHNOLOGY AND DESIGN Subject Code: 161004