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How can I have weak pull-down for used input IO PINs on cyclone V?



I'd like to add weak pull-down resistors for used input I/O pins on cyclone V. ​However, I can only find an optional programmable pull-up resistor for each I/O pin in handbook. Is there any way to add a weak pull-down resistor for used input I/O pins?

Also, there is an optional bus-hold feature.

  1. Can I define an inout port and have an initial output value, then change to input mode to let the input hold the value of the initial output?
  2. In this case, how high a voltage from the pin can stop holding the value?


Thanks and regards,


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3 Replies
Hello Ross, Thank you for questions,First I apologize for my delayed response. i am not sure why you are looking for pull down options , Here is the cyclone V pin out guidelines link below This is used to find the state the pin should if the pin are unused and also information about any external pull up /pull down requirement for Cyclone V. https://www.intel.com/content/dam/www/programmable/us/en/pdfs/literature/dp/cyclone-v/pcg-01014.pdf About the Bus hold , good question. From the block diagram of the IOE reference to figure 5-10, Assuming you have output (low impedance) of logic 1 and it set to hold the value...when you change to input buffer (i.e high impedance) i think there will be no problem to hold the logic if i understood correctly..but honestly i never tried on inout port. Can you kindly try and let me know ? Also let me know any if you have any other questions related to same topic ? Thank you , Regards, Sree

Hi Sree,


Thank you for your information.


Actually, I'm using an existing board that has a cyclone V device on it. I'd just like to have some input PINs to keep logic 1 and some others to keep logic 0 when there are no connections. I do it by program instead of hardware currently and I'd like to know if there are some other better ways to achieve this.


I also have interests on the features that I haven't used before, so I'll have a try to know about the Bus hold after this busy period and give you a feedback if I have any conclusion.


Thank you.


Best regards,


Hello Ross, Thank you much and let me know if you face any issue on the same :) regards, Sree