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AR# 45286

ISE Simulator - Port "Buffer" is not supported with ISIM

Description

Port "Buffer" is not supported with ISIM. The following errors occur:

"ERROR:HDLCompiler:439 - "C:/XXX/XXX/XX.vhd" Line 46: Formal port<xxx> of mode buffer cannot be associated with actual port<xxx> of mode out"

"ERROR:Simulator:777 - Static elaboration of top level VHDL design unitXX in library work failed"

Solution

Theseerrors can occurif any port is declared as abuffer.You might need to declare the VHDL buffered port as output and use an intermediate signal to perform read and write operation on it, and later assign the intermediate signal to the output port. See the following example:

entity alu is

port(

A : in STD_LOGIC_VECTOR(3 downto 0);

B : in STD_LOGIC_VECTOR(3 downto 0);

CLK : in STD_LOGIC;

C : buffer STD_LOGIC_VECTOR(3 downto 0) );

end alu;

architecture BEHAVIORAL of alu is

begin

process begin

if (CLK'event and CLK='1') then

C <= UNSIGNED(A) + UNSIGNED(B) UNSIGNED(C);

end if;

end process;

end BEHAVIORAL;

Modified code:

entity alu is

port(

A : in STD_LOGIC_VECTOR(3 downto 0);

B : in STD_LOGIC_VECTOR(3 downto 0);

CLK : in STD_LOGIC;

C : out STD_LOGIC_VECTOR(3 downto 0)

);

end alu;

architecture BEHAVIORAL of alu is

-- dummy signal

signal C_INT : STD_LOGIC_VECTOR(3 downto 0);

begin

C <= C_INT;

process begin

if (CLK'event and CLK='1') then

C_INT <= A and B and C_INT;

end if;

end process;

end BEHAVIORAL;

For more information on ports, see theSynthesis and Simulation Guide, as well as the ISIM User Guide.

AR# 45286
Date Created 01/30/2012
Last Updated 12/15/2012
Status Active
Type General Article
Tools
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