ibufgds.v

Clock data recovery .........good example

///////////////////////////////////////////////////////////////////////////////
// Copyright (c) 2003 Xilinx, Inc.
// All Rights Reserved
///////////////////////////////////////////////////////////////////////////////
//   ____  ____
//  /   /\/   /
// /___/  \  /    Vendor: Xilinx
// \   \   \/     Version: 1.0
//  \   \         Application : XAPP868
//  /   /         Filename: ibufgds.v
// /___/   /\     Timestamp: Thu Jan 17 2008
// \   \  /  \
//  \___\/\___\
//
///////////////////////////////////////////////////////////////////////////////

`timescale  100 ps / 10 ps


module IBUFGDS (O, I, IB);

    parameter CAPACITANCE = "DONT_CARE";   
    parameter DIFF_TERM = "FALSE";
    parameter IBUF_DELAY_VALUE = "0";
    parameter IOSTANDARD = "DEFAULT";
   
    output O;
    input  I, IB;

    reg o_out;

    buf b_0 (O, o_out);

    initial begin
	
        case (CAPACITANCE)

            "LOW", "NORMAL", "DONT_CARE" : ;
            default : begin
                          $display("Attribute Syntax Error : The attribute CAPACITANCE on IBUFGDS instance %m is set to %s.  Legal values for this attribute are DONT_CARE, LOW or NORMAL.", CAPACITANCE);
                          $finish;
                      end

        endcase

	
	case (DIFF_TERM)

            "TRUE", "FALSE" : ;
            default : begin
                          $display("Attribute Syntax Error : The attribute DIFF_TERM on IBUFGDS instance %m is set to %s.  Legal values for this attribute are TRUE or FALSE.", DIFF_TERM);
                          $finish;
                      end

	endcase

	
	case (IBUF_DELAY_VALUE)

            "0", "1", "2", "3", "4", "5", "6", "7", "8", "9", "10", "11", "12", "13", "14", "15", "16" : ;
            default : begin
                          $display("Attribute Syntax Error : The attribute IBUF_DELAY_VALUE on IBUFGDS instance %m is set to %s.  Legal values for this attribute are 0, 1, 2, ... or 16.", IBUF_DELAY_VALUE);
                          $finish;
                      end

        endcase
	
    end
    
    always @(I or IB) begin
	if (I == 1'b1 && IB == 1'b0)
	    o_out <= I;
	else if (I == 1'b0 && IB == 1'b1)
	    o_out <= I;
    end

endmodule