Strange effect with Stratix FPGA

All the above advise sounds reasonable.

I have found that for pre built "reference boads" it is wise to make sure that all pins that have external components connected to them ALWAYS have those pins fully assigned in the assignment editor. You need to add "extra" code to the design to properly drive outputs to pins that expect something (like your LED "." element). You need to also "catch" inputs and do something with them, anything will do.

This way, every external pin will not be flapping in the wind. (OK, inputs can be ignored if the device driving them has something like a CE (chip enable) that can be driven to tell the external device to stay quiet).

I hope this helps.

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