Why PXI 6509 DI Pin Does Not Change Its Digital State When High Level Voltage on It Is Removed?

Updated Oct 24, 2019

Reported In


  • PXI-6509
  • PCI-6509
  • PCIe-6509

Issue Details

We are having problem with Digital Input in PXI-6509. When we apply 5V to any of digital input pin, we can read high digital level in software. However, when we remove this voltage, pin retains its last digital level. Should it not return to low state when the voltage is removed? 


When the voltage from digital input pin of NI PXI-6509 is removed, it leaves the pin in floating state. As there are no pull-up or pull-down resistors available in NI PXI-6509, the pin can show any of digital state in software.

In order to solve this issue, use pull-up or pull-down resistors externally. A typical value of pull-up resistor is 4.7k Ohm while for pull-down resistor, 47k Ohm resistor value is recommended.

Above information is valid for:
1. PXI-6509
2. PCI-6509

Additional Information

Only PCIe-6509 contains internal software-programmable pull-up and pull-down resistors. Please consult product specification sheet for further details.