//2023-10-4   姜青羊
//case语句的多路选择逻辑

`timescale 1ns/10ps
module fn_sw (
                a   ,
                b   ,
                sel ,
                y
             );

input           a,b      ;
input[1:0]      sel      ;
output          y        ;

reg             y        ;

always @(a or b or sel) begin
    
    case(sel)
    2'b00:   y = a&b;    
    2'b01:   y = a|b;    
    2'b10:   y = a^b;   
    2'b10:   y = ~(a^b); 
    endcase

end
    
endmodule

//------------testbench--------------

module tb_fn_sw ();

reg[3:0]         absel ;
wire             y     ;

initial begin
                 absel <= 0;
        #200     $stop;
    
end

always  #10      absel <= absel+1; 



fn_sw u_fn_sw (
                .a(absel[0])   ,
                .b(absel[1])   ,
                .sel(absel[3:2]) ,
                .y(y)
             );

endmodule