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Simulation in modelsim.... Multiple Drivers.......

 
 
CODE_IS_BAD
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      04-21-2005
Hi all...
i have been trying to simulate some code in which there is a data bus

that is declared to be of INOUT type. I have simulated my VHDL code and

for both read and write operations it works fine, also the data bus
gets tri-stated (Z) when not in use.
Now this simulation was done by directly putting the values of signals

in the ModelSim environment. Then I thought to write a testbench to
simulate the same. In this case when I write some data on the databus
it does not get tri-stated when not in use. So i tried to debug the
problem and found that since in my testbench I am forcing some value on

the bus say '3B' and also in code i force 'Z' when not in use, then
STD_LOGIC being a resolved type resolves the value and gives '3B' since

'Z' has got least priority.
Why it worked directly on ModelSim environment was bcoz i was
"Depositing" the value on bus and not "Freezing" it. If i freeze the
value there then in that case also i cud not make the bus tri-stated.


So i would like to know how in our testbench we can write code such
that i can see all the correct results. I think in practice this will
work fine but it's better if in simulation also we can see the desired
results. Hope somebody can help. Thanx a lot
PUNEET

 
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