led闪烁实验

source code

module led(
    input          sys_clk  ,  //系统时钟
    input          sys_rst_n,  //系统复位，低电平有效

    output  [1:0]  led         //LED灯
);

//reg define
reg  [25:0]  cnt ;

//*****************************************************
//**                    main code
//*****************************************************

//对计数器的值进行判断，以输出LED的状态
assign led = (cnt < 26'd2500_0000) ? 2'b01 : 2'b10 ;
//assign led = (cnt < 26'd5)         ? 2'b01 : 2'b10 ;  //仅用于仿真

//计数器在0~5000_000之间进行计数
always @ (posedge sys_clk or negedge sys_rst_n) begin
    if(!sys_rst_n)
        cnt <= 26'd0;
    else if(cnt < 26'd5000_0000)
//  else if(cnt < 26'd10)  //仅用于仿真
        cnt <= cnt + 1'b1;
    else
        cnt <= 26'd0;
end

endmodule

xdc文件

set_property -dict {PACKAGE_PIN U18 IOSTANDARD LVCMOS33} [get_ports sys_clk]
set_property -dict {PACKAGE_PIN N16 IOSTANDARD LVCMOS33} [get_ports sys_rst_n]
set_property -dict {PACKAGE_PIN H15 IOSTANDARD LVCMOS33} [get_ports {led[0]}]
set_property -dict {PACKAGE_PIN L15 IOSTANDARD LVCMOS33} [get_ports {led[1]}]