uh-oh. Potential Zybo screwup

[engrpetero]

Hi all.  I've been away on boring mechanical eng tasks for the past two months.  Back on the more fun Zybo stuff now.

I think I've screwed up an interfacing issue with the Zybo PMOD port JF (the one connected to the MIO) and hoping someone might have a solution.

The picture below is from the Zybo schematic.  'A' shows the two on-board buttons and how they are connected to MIO pins.  There are pull-down resistors and a button press connects the pin to logic HI (1.8V in the case of the on-board buttons).  'B' shows the JF MIO PMOD port and 'C' simply shows the PMOD port JF's connections to the Zynq pins.

I have a simple interface board the Zybo connects to and it contains a similar push button arrangement, the thought being the pins are normally pulled down to GND and a button press connects the pin to logic HI.  Problem is I never see state changes on the JF MIO.  I DO, however, if I pull the pins low (almost as if they have an internal pull-up already on). 

I have tried setting the GPIO MIO pull-ups to ENABLED as well as DISABLED in the Vivado configuration but it doesn't seem to have the effect I want - the Zynq only seems to see state changes if I pull those pins to GND.  I fear I'll have to update my interface board but am hoping there is a way out.  Any ideas?

 

[engrpetero]

I played with this for a bit longer, enabling and disabling pull-ups in Vivado for the three MIO pins.  I see no real difference.  It's almost as if there is a 10K pull-up that doesn't respond to disabling.  I modified my hardware so my momentary-off pushbuttons 'pull-down' to GND.  That's the opposite of the 1.8V MIO buttons 4,5 on the ZYbo as well as the 3.3V buttons 0,1,2,3 on the Zybo but I can't get it to work if I don't make those changes.  Something fishy going on there. 

I don't need any immediate help with this - the solution I went with works.  But perhaps sometime in the future, someone can figure out why I couldn't implement the same design shown for buttons 0,1,2,3.

Edited November 29, 2023 by engrpetero