Vhdl what is x

I am studing vhdl. And does X show hegzadecimal? I read some and am expecting leading information about lcd driver from your help. Re: help for fpga shsshs said:.

Click to expand Re: help for fpga when I synthesize the code it does not give any error. As a result of this I decide that this representation and assignment are correct.

Re: help for fpga uoficowboy: you are right. And about the initialization method used,this is a normal method of initializing arrays or vectors. The "others" key word is used to assign a value to all other bits or indexes the specified value. I hope it is clear now. TrickyDicky Advanced Member level 5. Re: help for fpga if you are new to FPGA Thank you very much for your help. We obly need the source files.

I'd already repaired it. Its a simple problem, and not a problem with the code. As soon as B changes to non-zero, the output is valid. If you initilise B to something non-zero, there is no problem. The output should be correct. You can see my first post in this thread. I did not know why? Could you help me? The code you have posted has nothing to do with mine. Load more replies. Post Reply. Add some interesting internal signals to the Wave window and see what they are doing.

Start with the ALU signals since Jonathan points at it. See where the Xes come from, try his recommendations and see if they disappear. Debugging using internal signals si an important skill to develop,.

Add a comment. Active Oldest Votes. Improve this answer. Jonathan Drolet Jonathan Drolet 3, 1 1 gold badge 9 9 silver badges 20 20 bronze badges. Sign up or log in Sign up using Google. Sign up using Facebook. Sign up using Email and Password.

Post as a guest Name. Email Required, but never shown. My general rule of thumb is "if I can imagine the logic to implement this piece of code, then the synthesizer probably can too". Here I cannot envision the logic do to what you're asking, which is "if the input is the number N , then set bit N of the output and set all other bits to zero". You can confirm this looking at the synthesized design schematic from your synthesis tool.

Show 6 more comments. Active Oldest Votes. Is there a way to know what would be the state of this signal at the power-on? And is there a way to set this power-on state in code? What it picks is usually available in the synthesis report. To set the default state in VHDL you would use Do you know how is synthesized such an initialization? What would the circuit that initializes a signal look like?

Add a comment. Lastly, VHDL has the dedicated "don't care" value of '-', which is purely used as a hint to the synthesizer to help optimize the logic. So, revisiting your questions: Your first question directly translates to "when I have unknown logic signals, what is the equivalent integer value? Your second question translates to "can I set the output to 0 when the input is unknown?

In simulation, an "unknown" value is a useful assistance to make sense of what's going on and catch flaws in the design. The others have already ably answered this question, and I've repeated it somewhat here: by definition the physical input cannot see 'U' or 'X', just '0' and '1'. Snrub Mr. Snrub 2, 6 6 silver badges 11 11 bronze badges.