Forum Discussion
HAlex
Occasional Contributor
Occasional ContributorUnconnected inputs of Cyclone III
Hello I am using EP3C40F484C8N FPGA in my board. As now I want to remove some components assembled on PCB and connected to the FPGA inputs I want to know what modifications must be done in my Quart...
I will leave these pins defined as inputs (for any case) and will assign an internal weak pull up on them.
FvM
Super Contributor
Super ContributorUnconnected pin behaviour is set in device and pin options dialog, tri-stated with weak pull-up is the default option and fits most cases. For pins connected to FPGA fabric, the option can be set in assignment editor or pin planner. Consider that Cyclone 3 clock inputs have no weak pull-up feature and should be externally connected if ever possible.
HAlexOccasional Contributor
Occasional ContributorHello
The option in device and pin dialog is for unused pins. In my case I have a defined inputs, some of them are connected to the FPGA logic (but actually not used by Nios or not effect on any essential output). FPGA doesn't know that the inputs are going to be disconnected. My question is if I need to recompile my FPGA (and remove unconnected pins/define them as weak pull-ups) or simply do nothing and leave design as is without recompilation?
Thank you.
Alex
- FvMFloating inputs can cause additional current consumption and switching noise. Therefore you want to avoid floating inputs by any available means.
