button_pio.v

基于Nios II的汽车智能防盗导航系统核心作为嵌入式系统发展趋势

//Copyright (C) 1991-2004 Altera Corporation
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//support information, device programming or simulation file, and any other
//associated documentation or information provided by Altera or a partner
//under Altera's Megafunction Partnership Program may be used only to
//program PLD devices (but not masked PLD devices) from Altera.  Any other
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//any other related documentation or information provided by Altera or a
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// synthesis translate_off
`timescale 1ns / 100ps
// synthesis translate_on
module button_pio (
                    // inputs:
                     address,
                     clk,
                     in_port,
                     reset_n,

                    // outputs:
                     readdata
                  );

  output  [  3: 0] readdata;
  input   [  1: 0] address;
  input            clk;
  input   [  3: 0] in_port;
  input            reset_n;

  wire             clk_en;
  wire    [  3: 0] data_in;
  wire    [  3: 0] read_mux_out;
  reg     [  3: 0] readdata;
  assign clk_en = 1;
  assign read_mux_out = {4 {(address == 0)}} & data_in;
  always @(posedge clk or negedge reset_n)
    begin
      if (reset_n == 0)
          readdata <= 0;
      else if (clk_en)
          readdata <= read_mux_out;
    end


  assign data_in = in_port;


endmodule