Table Of Contents

USB-6251 Screw Terminal Pinout

    Last Modified: March 21, 2017

    Table 1. Default Counter/Timer Terminals
    Counter/Timer Signal Default PFI Terminal
    CTR 0 SRC PFI 8
    CTR 0 GATE PFI 9
    CTR 0 AUX PFI 10
    CTR 0 OUT PFI 12
    CTR 0 A PFI 8
    CTR 0 Z PFI 9
    CTR 0 B PFI 10
    CTR 1 SRC PFI 3
    CTR 1 GATE PFI 4
    CTR 1 AUX PFI 11
    CTR 1 OUT PFI 13
    CTR 1 A PFI 3
    CTR 1 Z PFI 4
    CTR 1 B PFI 11
    Table 2. Signal Descriptions
    Signal Reference Description

    AI GND

    Analog Input Ground—These terminals are the reference point for single-ended AI measurements in RSE mode and the bias current return point for DIFF measurements. All ground references—AI GND, AO GND, and D GND—are connected on the device.

    AI <0..15>


    Analog Input ChannelsFor single-ended measurements, each signal is an analog input voltage channel. In RSE mode, AI GND is the reference for these signals. In NRSE mode, the reference for each AI signal is an AI SENSE.

    For differential measurements, AI 0 and AI 8 are the positive and negative inputs of differential analog input channel 0. Similarly, the following signal pairs also form differential input channels: AI <1,9>, AI <2,10>, and so on.


    Analog Input SenseIn NRSE mode, the reference for each AI <0..15> signal is AI SENSE.

    AO <0,1>

    AO GND

    Analog Output Channels—These terminals supply voltage output.

    AO GND

    Analog Output GroundAO GND is the reference for AO. All ground references—AI GND, AO GND, and D GND—are connected on the device.

    D GND

    Digital GroundD GND supplies the reference for port 0, port 1, port 2 digital channels, PFI, and +5 V. All ground references—AI GND, AO GND, and D GND—are connected on the device.


    D GND

    Port 0 Digital I/O ChannelsYou can configure each signal individually as an input or output.

    APFI 0

    AO GND or AI GND

    Analog Programmable Function Interface ChannelsEach APFI signal can be used as AO external reference inputs for AO, or as an analog trigger input. APFI are referenced to AI GND when they are used as analog trigger inputs. APFI are referenced to AO GND when they are used as AO external offset or reference inputs.

    +5 V

    D GND

    +5 V Power Source—These terminals provide a fused +5 V power source.

    PFI <0..7>/P1.<0..7>, PFI <8..15>/P2.<0..7>

    D GND

    Programmable Function Interface or Digital I/O Channels—Each of these terminals can be individually configured as a PFI terminal or a digital I/O terminal.

    As an input, each PFI terminal can be used to supply an external source for AI, AO, DI, and DO timing signals or counter/timer inputs. As a PFI output, you can route many different internal AI, AO, DI, or DO timing signals to each PFI terminal. You can also route the counter/timer outputs to each PFI terminal. As a port 1 or port 2 digital I/O signal, you can individually configure each signal as an input or output.

    Table 3. LED State/Device Status
    ACTIVE READY Device Status
    Off Off Device is not powered or not connected to the host computer, or the host computer does not have the correct driver version. Detection can take 30 to 45 seconds.
    Off On Device is configured, but there is no activity over the bus.
    On On Device is configured and there is activity over the bus.
    Blinking On

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