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433 Views
Registered: ‎09-16-2019

Input pin always high

Hello, 

I am using a KC705 development board to test an interface for a flash memory IC. I'm using the FMC105 debug card for I/O. I'm having a problem where one input pin is reading high at all times. Even with the FMC105 card removed, the pin still reads high. I've tried changing the "Pull Type" in the IO Ports window from the default of "none" to "pull-down" but the pin still reads high at all times. I have simulated this design and do not see this issue so it's unlikely an issue with my HDL. 

Does anyone have any ideas what my issue is and how to correct it? 

 

Thank you,

David  

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5 Replies
u4223374
Advisor
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404 Views
Registered: ‎04-26-2015

davidfhorowitz@lmco.com Have you checked the actual level on that pin with a multimeter? It would be good to know whether it's actually high all the time (eg. stray piece of wire bridging it to a power rail?) or just being reported as high all the time (ie. either a configuration issue or physical damage to the chip).

 

What I/O standard is it, and what voltage is the bank running at? Do other pins in the same bank behave properly?

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369 Views
Registered: ‎09-16-2019

With a multi-meter I read no voltage on the physical pin. The I/O standard is set to CMOS25. The other pins in the bank behave properly, though they are set as outputs. I've tried changing pins for the input and get the same results. So it's reporting high at all times though it physically isn't high.  

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362 Views
Registered: ‎07-23-2019

"I read no voltage on the physical pin"

Do you mean 0.00V by that?

One thing to check is there is a pull-up somewhere in the circuit or in the I/O itself.

I would first suspect of the design itself before suspecting damage.

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359 Views
Registered: ‎07-23-2019

Can I suggest a quick test to discard damage?

You make a clock and output it (actually a signal that toggles) to an FMC pin, then you have your pin input copied to another output pin (or with a division by two, whatever). You connect externally the clock to the input and check the output with a scope.

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348 Views
Registered: ‎09-16-2019

By "no voltage" I mean effectively no voltage as in 0.12 V or something very small that fluctuates that you typically see on the multi-meter when its connected to nothing. 

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