Learn more about making digital input/output measurements with the USB-6421.

Digital Input Data Acquisition Methods
When performing digital input measurements, you either can perform software-timed or hardware-timed acquisitions.
Digital Waveform Acquisition
You can acquire digital waveforms on the digital I/O lines. You can configure each digital I/O line to be an output, a static input, or a digital waveform acquisition input.
Digital Input Change Detection
You can configure the USB-6421 to detect changes on all 16 digital input lines (P0).
Digital Input Timing Signals
The USB-6421 features five digital input timing signals.
Digital Output Data Generation Methods
When performing a digital waveform operation, you either can perform software-timed or hardware-timed generations.
Digital Waveform Generation
You can generate digital waveforms on the digital I/O lines. The digital output waveform generation FIFO stores the digital samples.
Digital Output Timing Signals
The USB-6421 features four digital output (waveform generation) timing signals.
I/O Protection
Each digital I/O signal is protected against overvoltage, undervoltage, and overcurrent conditions as well as electrostatic discharge (ESD) events.
Digital I/O Signal Connections
The digital I/O signals are referenced to D GND. You can individually program each line as an input or output.
Using Digital I/O Terminals as Timing Input Signals
Use digital I/O terminals to route external timing signals to many different functions.
Using Digital I/O Terminals to Export Timing Output Signals
Filters for Digital Input
You can enable a programmable debouncing filter on each digital line on Port 0. These filters are available when you use the digital line for input.
Filters for Counter and Timer Signals
You can enable programmable debouncing filters on each DIO <0..15> signal. These filters are available when you use a DIO <0..15> signal as a counter, timer, or trigger signal.
Watchdog Timer
Use the watchdog timer to set critical outputs to a safe state if software fails, a system crashes, or the application loses communication with the USB-6421.
Digital Input/Output Logic Families
You can configure the digital voltage of the USB-6421 by selecting logic families on the USB-6421. The logic family configuration affects the digital input, digital output, counter input, counter output, and trigger functions.
Programmable Power-Up States
At system start up and reset, the hardware sets all digital I/O lines to high-impedance inputs by default.

USB-6421 and USB-6421 (OEM) User Manual

16-Bit, 250 kS/s (16 AI, 2 AO, 16 DIO) mioDAQ, USB Multifunction I/O Device