Programmable Levels

You can program the pin driver with the following pin levels using the NI-Digital Pattern Driver or set pin levels interactively in Digital Pattern Editor. Pin levels are programmable per pin or by pin group.

  • VIH—Specifies the voltage that the instrument applies to the input of the DUT when the instrument drives a logic high (1).
  • VIL—Specifies the voltage that the instrument applies to the input of the DUT when the instrument drives a logic low (0).
  • VTERM—Specifies the termination voltage the instrument applies during non-drive cycles when the termination mode is set to VTERM. The instrument applies the termination voltage through a 50 Ω parallel termination resistance.

The NI-Digital Pattern Driver does not enforce a minimum separation between VIH and VIL. Refer to PXIe-6570 Specifications for information about the minimum separation required for reliable results.

The following diagram illustrates pin levels as they relate to the digital pattern instrument and the DUT.



Initial State

On power-up, pins are in a high-impedance state. To avoid unexpected results for DUTs that are sensitive to the initial state of a pattern burst, programmatically specify the initial pin state by using the niDigital Write Static VI, the DigitalPinSet.WriteStatic .NET method, or the niDigital_WriteStatic C function.

You can interactively set the initial state for a pin by selecting the corresponding driver symbol in the Drive section of the Pin View pane of the Digital Pattern Editor. After each pattern burst, the ending state of the last executed vector persists until the start of the next pattern burst or until you programmatically or interactively change the pin state or pin function.

Termination Mode

The termination mode specifies the behavior of the pin when the pin function is set to Digital and the current pin state is not a drive state. Non-drive states include L, H, M, V, X and potentially -. Pattern data and the termination mode determine the full behavior of the pin. You can set the following termination modes interactively in the Digital Pattern Editor or programmatically with the NI-Digital Pattern Driver:

  • High Z—Specifies that, for non-drive pin states (L, H, X, V, M, E), the pin driver is put in a high-impedance state and the active load is disabled.
  • Active Load—Specifies that, for non-drive pin states (L, H, X, V, M, E), the active load is connected and the instrument sources or sinks a defined amount of current to load the DUT.
  • IOL—Specifies the amount of current sourced by the instrument and therefore sunk by the DUT.
  • IOH—Specifies the amount of current sunk by the instrument and therefore sourced by the DUT.
  • VCOM—Specifies the voltage at which the instrument changes between sourcing and sinking.
  • VTERM—Specifies that, for non-drive pin states (L, H, X, V, M, E), the pin driver terminates the pin to the configured VTERM voltage through a 50 Ω impedance. VTERM is adjustable to allow for the pin to terminate at a set level. This is useful for devices that might operate incorrectly if an instrument pin is unterminated and is allowed to float to any voltage level within the instrument voltage range. To address this issue, enable VTERM by configuring the VTERM pin level to the desired voltage and selecting the VTERM termination mode. Setting VTERM to 0 V and selecting the VTERM termination mode has the effect of connecting a 50 Ω termination to ground, which provides an effective 50 Ω impedance for the pin. This can be useful for improving signal integrity of certain DUTs by reducing reflections while the DUT drives the pin.

    • For more information about terminating digital pattern instruments, visit ni.com/info and enter the Info Code InstrumentTermination to access Terminating Digital Pattern Instruments.