Johnson Counter / shift counter

Block diagram for Johnson Counter:

Present state {reset,q}	Next state q
00000	1000
01000	1100
01100	1110
01110	1111
01111	0111
00111	0011
00011	0001
00001	0000
Default for other values even if reset=1	0000

Verilog code for Johnson Counter / shift counter:

module johnson_counter(

    input clock,

    input reset,

    output reg [3:0] q );

always@(posedge clock)

begin

case ({reset,q})

5'b00000:q=4'b1000;

5'b01000:q=4'b1100;

5'b01100:q=4'b1110;

5'b01110:q=4'b1111;

5'b01111:q=4'b0111;

5'b00111:q=4'b0011;

5'b00011:q=4'b0001;

5'b00001:q=4'b0000;

default:q=4'b0000;

endcase

end

endmodule