分析以上程序，若想设置流水灯的状态为16种，则st 的位宽应设置为_____________。 module LED(clk,rst,led,dig,seg); input clk,rst; output reg[7:0] led; output reg[7:0] dig; output reg[7:0] seg; reg[24:0] t; reg clk_1hz; reg[2:0] st; //分频程序 always @(posedge clk) begin if(t == 25000000-1) begin t <= 0; clk_1hz <= ~clk_1hz; end else t <= t + 1; end always @(posedge clk_1hz) begin if(!rst) st <= 0; else st <= st + 1; case(st) 0:begin led <= 8'b11111110; dig <= 8'b11111110; seg <= 8'hf9; end 1:begin led <= 8'b11111101; dig <= 8'b11111101; seg <= 8'ha4; end 2:begin led <= 8'b11111011; dig <= 8'b11111011; seg <= 8'hb0; end 3:begin led <= 8'b11110111; dig <= 8'b11110111; seg <= 8'h99; end 4:begin led <= 8'b11101111; dig <= 8'b11101111; seg <= 8'h92; end 5:begin led <= 8'b11011111; dig <= 8'b11011111; seg <= 8'h82; end 6:begin led <= 8'b10111111; dig <= 8'b10111111; seg <= 8'hf8; end 7:begin led <= 8'b01111111; dig <= 8'b01111111; seg <= 8'h80; end default:begin led <= 8'b11111111; dig <= 8'b11111111; seg <= 8'hff; end endcase end endmodule