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Bidirectional PIO

Honored Contributor II

Hai all, 

I am using cyclone IV fpga for my project and i am using a custom made development board .In that i have configured 16 number of pins as bidirectional PIO's.These pins i have not pulled up externally to Vcc.If i configure the PIO's as output only and try to output to these PIO's then the voltage level of these pins are at 2.5V.If i configure them to bidirectional and make the direction as output in the PIO register ,then try to output a value,the voltage level of these pins are stuck at 1.2V .What can be the reason for this? Why the voltage level drops to 1.2V from 2.5V? How to rectilfy this? 


Thanks in advance.
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Honored Contributor II

Indeed, that's not right. Setting the PIO as an output and setting it high and low should behave as you expect. 


Is the PIO part of a Nios core? How is it instantiated in your code - or is your Qsys module the top level of your design? 


If instantiated, check you've not connected your exported PIO connection to an input signal at your top level. Pins configured as input signals can sometimes float mid-rail. 


If your Qsys module is the top level then perhaps you're not controlling the PIO module from your software correctly. 


I think (hope) this should be fairly straightforward to track down. 



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