Can the voltage level of each channel of the PXIe-6535 card be set individually (i.e. can one channel be set to 2.5V and another be set to 3.3V simultaneously)?
Are you talking about for what is considered active high and active low? I don't think you can. The only way functions I saw on how to configure that setting all had the device name as the parameter, so I think the device takes that setting as a whole.
