Vhdl Ram

Hello,

I am having trouble with a RAM component that I created from a datasheet. The code for the component can be found below. The trouble I am having occurs when I try to write into the memory. If the chip enable (cen) is placed low before the write enable (wen), when the write enable goes low, the input goes undefined. This happens when there is data already in the memory or not. If both cen and wen are placed low at the same time, the write occurs as it should. Any insight as to what causes this problem would be appreciated. Thanks.



ENTITY mil_11570287_2_1024x4_sram_b IS

PORT(
addr : IN std_logic_vector (9 DOWNTO 0);
cen : IN std_logic;
wen : IN std_logic;
I : INOUT std_logic_vector (4 DOWNTO 1)
);

END mil_11570287_2_1024x4_sram_b ;


ARCHITECTURE arch OF mil_11570287_2_1024x4_sram_b IS

type mem_array is array(0 to 1023) of std_logic_vector(4 downto 1);
signal sram_values: mem_array;

BEGIN

process(cen, wen, I, sram_values, addr)
begin
if cen = '0' then
if wen = '0' then
sram_values(conv_integer(unsigned(addr))) <= I;
else
I <= sram_values(conv_integer(unsigned(addr)));
end if;
else
I <= (others => 'Z');
end if;
end process;

END ARCHITECTURE arch;

bmartiniello