I have a design with ARRIA 10 and I need to have the nIO_PULLUP to HIGH to turn off the weak pull-up before and during configuration. But I cannot ensure that all user I/O pins are at valid logic (0 or 1). What problem may I have?

Hi AKarv,

I'm apologize for later reply to this thread.

The potential problem you may have is crowbar(short-circuit) current in the I/O input buffer.

When nIO_PULLUP=1 (HIGH), all user I/Os float before configuration. When user I/Os are floating before configuration, there is crowbar current at user I/Os buffer. Therefore, we need to set the user I/O externally known state (valid logic 1 or 0) to avoid internal crowbar current.

Also I would like to ask if I can enable after configuration the internal weak pullups at specific input pins even if nIO_PULLUP is HIGH.

Ans: No, you cannot enable after configuration the internal weak pullups if nIO_PULLUP is HIGH. You need set nIO_PULLUP to LOW is you need to enable internal weak pullup.

I hope this will help.

Thanks