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724 Views
Registered: ‎09-25-2018

What is the meaning of "xxxxxx" in the output signal?

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2 Replies
Scholar dpaul24
Scholar
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Registered: ‎08-07-2014

Re: What is the meaning of "xxxxxx" in the output signal?

@mehmedsamil55,

It means the state is "Unknown".

Set  cikis to 32 bit 0s where you are declaring this register and you won't see it again.

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Moderator
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Registered: ‎11-09-2015

Re: What is the meaning of "xxxxxx" in the output signal?

Hi @mehmedsamil55 ,

To give more details to @dpaul24 's reply:

"X" means unknown. You will get this result when you do not know if the bit will be 0 or 1. This is only a simulation value. In HW you will only get a 0 or a 1.

"X" will happen if you do any operation on an uninitialized ("U") value (as it seems to be the case in your simulation) because you do not know what will be the value at initialization.

It might also happen if 2 different signals are driving the same signal. You do not know which one will have the priority.

As @dpaul24 said, usually, if you give a default value to your signals, you will get rid off most "X" in your simulation. You can just give the value 0 when you declare the signals.

But note that some people do not care about this when it is in the begining of the simulation, it is just the time to have all signals initialized by the system.

Hope that helps,


Florent
Product Application Engineer - Xilinx Technical Support EMEA
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