bidirectional bus problem

[fatihtir]

Hello all,

Could you please tell me the difference between two lines below:

sram_da <= write_data when (sram_read='0') else "ZZZZZZZZZZZZZZZZ";
sram_da <= "ZZZZZZZZZZZZZZZZ" (sram_read='1) else write_data;

I used the first line for reading from sram, but simulation didn't showed expected result (i have an sram vhld model also). After long hours of examination and trying, when i replaced it with second line, it was ok. But I can't understand why the first line is wrong.

I appreciate your help.

Regards.


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[tomeko]

Hi Fatihtir,
:listen:
what type is the sram_read signal in your project ?
If it is std_logic, then bear in mind that it can have 9 possible values
(besides '0' and '1', also 'H', 'L', '-', 'X', 'Z', 'U', 'W').
This might justify the resuts of your simulation (perhaps).
Regards.