pullup.vhd

IIC的IP.这是经过验证的源代码

------------------------------------------------------------------------------
-- 
--  Name:  pullup.vhd  
-- 
--  Description:  Emulate Pullup on the IO
-- 
--  $Revision: 1.0 $          
--  
--  Copyright 2004 Lattice Semiconductor Corporation.  All rights reserved.
--
------------------------------------------------------------------------------
-- Permission:
--
--   Lattice Semiconductor grants permission to use this code for use
--   in synthesis for any Lattice programmable logic product.  Other
--   use of this code, including the selling or duplication of any
--   portion is strictly prohibited.
--
-- Disclaimer:
--
--   This VHDL or Verilog source code is intended as a design reference
--   which illustrates how these types of functions can be implemented.
--   It is the user's responsibility to verify their design for
--   consistency and functionality through the use of formal
--   verification methods.  Lattice Semiconductor provides no warranty
--   regarding the use or functionality of this code.
------------------------------------------------------------------------------
--
--    Lattice Semiconductor Corporation
--    5555 NE Moore Court
--    Hillsboro, OR 97124
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--    TEL: 1-800-Lattice (USA and Canada)
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------------------------------------------------------------------------------

library ieee;
use ieee.std_logic_1164.all;
use ieee.std_logic_unsigned.all;

entity pullup is
        port (Enb : in std_logic;
              O : out std_logic);
end;

architecture beh of pullup is
begin
  O <= 'H' when (Enb= 'Z' or Enb = 'H') else 'Z' after 2 ns;

end;

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