J21 pull-up or down

hello everybody,
I need some help,
I uesd J21 as gpio,like pin-18 "MDM_WAKE_AP_LVL "
in “JetsonTX1_TX2_Developer_Kit_Carrier_Board_Specification.pdf” page 26, table 18.
pin-18 Power-on Default State is PD,
External PU/PD on carrier board is 1MΩ to GND,
so,should I need to uesd a additional resistance ? or not ?

Hi, this 1Mohm means R331 on carrier board. Are you designing your own carrier board? If so, there should be a PD to it.

Hello Trumany,
so you means there is a resistance on tx2 board as PD ?
If I uesd the pin to do somethin,I don’t need to pulldown by myself ?
But when I used pin16、18、31 as input pin,
if the pin is floating,the input signal is unstable,sometimes is high or low,
so what should I do,If I uesd the pin as GPIO ?
If I should used a pulldown resistance,what value is recommend ?

Are you using dev kit or your own designed board? No need to add PD on dev kit.

dev kit.
so what happen to my dev kit at J21,when I used the pin as input,and is unstable ?

It’s default low when used as input…

Not this situation,
sometimes it was high when the pin is floating.

The pin is not float…it has a PD on board (R331)

Now I used pin-16 18 31
3 pins are input
pin-16 and 18 power on default state is PD.
pin-31 default state is Z.
I set it input,and print state,the signal show me 16=0 18=0 31=1,
I don’t send any signal to 3 pins.
so what happen is it ?

Please check the schematic first. There is PU on the net of pin 31.