Errata e50080. Should external resistors be used on unused IO when peripheral are powered by 3.3V?

[pavel_yakushin]

I want to use SAI2_RXFS as PCI_nRST and SAI2_RXC as ENET_nRST, this signals should be 3.3V otherwise I have to use level translator. In the base board schematic SAI2 powered by 1.8V and level translator used and also can be used internal pull-up/down resistors.

I don't want to use level translator, I think to power on SAI2 from 3.3V, but I don't know whether I have to use external pulls for unused SAI2 IOs or can use internal pull-up or pull-down? Errata doesn't say anything about internal pulls for unused IO.

Please clarify this moment.

[pantarun_92]

1. Datasheet mentions does not support internal pullup or pulldown for 3.3V IOs on page 28 Table 20. Is it mandatory to use external pull ups or it is optional for 3.3V powered peripherals?
2. Above how much PCB trace length external pullup is mandatory?
3. What should be the appropriate pull up value?

[pantarun_92]

1. Datasheet mentions 'does not support internal pull-up or pull-down for 3.3 V IOs' on page 28, Table 20. Is it mandatory to use external pull ups       or it is optional for 3.3V powered peripherals?

2. Above how much PCB trace length external pullup is mandatory?

3. 

[igorpadykov]

Hi Pavel

external pulls for unused pins are not necessary.

Best regards
igor
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[pavel_yakushin]

Thanks a lot for your answer!

Сould you clarify a little more this moment please:

can I use internal pull to prevent IO floating (for 3.3V powered peripherial)?

[igorpadykov]

yes it can be used.