Digital Output changes with read

[MCalvino]

Hi,

When I use the test panel in NI MAX 20.0 of my PXIe-6509 I have this strange behavior : I set a port as output, all LOW, then I change to input and after few seconds, some lines change to HIGH.

Not all lines and all ports have this behavior. Nothing is connected to the board. Start-up mode is tristate.

Is this behavior normal ? Setting a digital output then reading it shouldn't change the state right ?

[santo_13]

That is expected.

If you don't have any signal connected when you read the input, the state is always indeterminate due to the high impedance unless you have a large capacitance or pull-up or pull-down resistor.