PCIe-6509 I/O Pull-Up/Pull-Down Resistors

The PCIe-6509 has user-configurable pull-up and pull-down resistors. The DIO lines on the PCIe-6509 are connected to an NI ASIC that contains a weak pull-down resistor (47 kΩ, typical), and each DIO line is connected to a software-selectable strong pull-up resistor (4.7 kΩ, typical), as the following figure shows.

Figure 2. PCIe-6509 Digital I/O Circuitry

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If you set the software to pull-down, the weak pull-down resistor in the NI ASIC pulls the DIO line low. If you set the software to pull-up, the strong pull-up resistor pulls the DIO line high. You can set the pull setting regardless of the I/O direction, but it affects only the state of DIO lines that are configured for input.