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Verilog

// Example of a 5-state Mealy FSM

module mealy (data_in, data_out, reset, clock);

output data_out;

input [1:0] data_in;

input reset, clock;

reg data_out;

reg [2:0] pres_state, next_state;

parameter st0=3'd0, st1=3'd1, st2=3'd2, st3=3'd3, st4=3'd4;

// FSM register

always @ (posedge clock or negedge reset)

begin: statereg

if(!reset)// asynchronous reset

pres_state = st0;

else

pres_state = next_state;

end // statereg

// FSM combinational block

always @(pres_state or data_in)

begin: fsm

case (pres_state)

st0:    case(data_in)

2'b00:       next_state=st0;

2'b01:       next_state=st4;

2'b10:       next_state=st1;

2'b11:       next_state=st2;

endcase

st1:    case(data_in)

2'b00:       next_state=st0;

2'b10:       next_state=st2;

default:     next_state=st1;

endcase

st2:    case(data_in)

2'b0x:       next_state=st1;

2'b1x:       next_state=st3;

endcase

st3:    case(data_in)

2'bx1:       next_state=st4;

default:     next_state=st3;

endcase

st4:    case(data_in)

2'b11:       next_state=st4;

default:     next_state=st0;

endcase

default:                     next_state=st0;

endcase

end // fsm

// Mealy output definition using pres_state w/ data_in

always @(data_in or pres_state)

begin: outputs

case(pres_state)

st0:    case(data_in)

2'b00:      data_out=1'b0;

default:     data_out=1'b1;

endcase

st1:      data_out=1'b0;

st2:    case(data_in)

2'b0x:      data_out=1'b0;

default:     data_out=1'b1;

endcase

st3:      data_out=1'b1;

st4:    case(data_in)

2'b1x:      data_out=1'b1;

default:     data_out=1'b0;

endcase

default:                     data_out=1'b0;

endcase

end // outputs

endmodule

Verilog

// Example of a 5-state Moore FSM

module moore (data_in, data_out, reset, clock);

output data_out;

input [1:0] data_in;

input reset, clock;

reg data_out;

reg [2:0] pres_state, next_state;

parameter st0=3'd0, st1=3'd1, st2=3'd2, st3=3'd3, st4=3'd4;

//FSM register

always @(posedge clock or negedge reset)

begin: statereg

if(!reset)

pres_state = st0;

else

pres_state = next_state;

end // statereg

// FSM combinational block

always @(pres_state or data_in)

begin: fsm

case (pres_state)

st0:    case(data_in)

2'b00:       next_state=st0;

2'b01:       next_state=st4;

2'b10:       next_state=st1;

2'b11:       next_state=st2;

endcase

st1:    case(data_in)

2'b00:       next_state=st0;

2'b10:       next_state=st2;

default:     next_state=st1;

endcase

st2:    case(data_in)

2'b0x:       next_state=st1;

2'b1x:       next_state=st3;

endcase

st3:    case(data_in)

2'bx1:       next_state=st4;

default:     next_state=st3;

endcase

st4:    case(data_in)

2'b11:       next_state=st4;

default:     next_state=st0;

endcase

default:                     next_state

=st0;

endcase

end // fsm

// Moore output definition using pres_state only

always @(pres_state)

begin: outputs

case(pres_state)

st0:     data_out=1'b1;

st1:     data_out=1'b0;

st2:     data_out=1'b1;

st3:     data_out=1'b0;

st4:     data_out=1'b1;

default: data_out=1'b0;

endcase