Digital I/O for Test, Control, and Design

Whether generating advanced patterns to characterize a custom circuit, toggling control lines to automate a factory floor, or prototyping a digital design, many applications require some degree of digital input and output capability. One of the most important steps in developing these applications is determining which device provides the best solution for your needs. National Instruments provides a wide range of digital I/O (DIO) products with different speed, voltage, and timing options to meet the digital needs of your test, control, and design applications.

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Digital I/O for Test and Measurement

Most digital automated test equipment (ATE) systems generate and/or acquire patterns of 1’s and 0’s to communicate with a DUT (device under test). With recent innovations in digital components, however, these systems require a more sophisticated digital tester with capabilities beyond a simple logic analyzer with two on/off states. Faster chip speeds and the industry trend toward serial vs. parallel digital protocols are necessitating ever higher sampling rates.  In addition, manufacturing and time-to-market pressures are demanding hardware-level processing to complete tests quicker. Meanwhile, new logic families with variable voltage levels and single or differential signaling continue to make these tests more complex. National Instruments High-Speed Digital I/O (HSDIO) devices offer a range of digital ATE and stimulus-response features designed to meet the requirements of these high-end digital test applications.

• High clock and data rates up to 200 MHz and 400 Mb/s, respectively, deliver precise hardware-timed control essential for testing the latest integrated circuits, FPGAs, and digital communication devices.
• Per-cycle, per-channel bidirectional control and real-time hardware comparison of acquired response data facilitate the development of applications such as bit error rate testing (BERT), failure analysis for verification and validation (V&V), and pass/fail manufacturing tests.
• Programmable voltage levels between -2.0 V and 5.5 V create a flexible digital system that can interface with multiple logics families or characterize the upper and lower bounds of specific DUT.

Figure 1. Programmable voltage levels of teh NI 655x devices

• Differential data transmission interfaces directly to the low-voltage, differential signals of high-speed LVDS (low-voltage differential signaling) electronics.
• Deep onboard memory based on the Synchronization and Memory Core  (SMC) hardware architecture can store large, complex waveforms and instructions in the same physical memory.
• Data delay allows you to phase shift acquisition, generation, and clock channels with respect to each other to measure setup and hold times, measure propagation delays, and maximize timing margins in high-speed data transfers.

Figure 2. Data delay of generated or acquired waveforms

• Six logical channel states including logic low (0), logic high (1), tri-state (Z), compare logic high (H), compare logic low (L), and ignore (X) define digital test waveforms and control the actions of the digital tester.
• Multi-device synchronization offers down to sub-nanosecond synchronization for high-channel count systems without the need for external wiring.
• Flexible handshaking modes provide synchronous and asynchronous exchange of signals to request and acknowledge data transfers between the test system and DUT.

Software is also a critical piece of any digital ATE. The Digital Waveform Editor is a graphical software tool you can use to visualize digital signals and easily create, edit, and modify digital waveforms for customized interfacing and test applications. You can design digital waveforms from scratch or import existing waveforms from design tools using Value Change Dump (.VCD) or ASCII file formats. In addition, as you acquire data, the Digital Waveform Editor can highlight bit errors, making it easy to visualize inconsistencies and measure timing requirements or update waveforms to eliminate design flaws. Combined with LabVIEW and NI TestStand, the waveform editor completes the software component of any digital test system.

Click here to learn how EDA Industries created a flexible digital test system for a key European defense contractor using High-Speed Digital I/O hardware and LabVIEW Software.

To learn more about specific High-Speed Digital I/O product families, refer to the table below.

Family	Bus	Max Data Rate	Voltage Levels	# Channels	Max Onboard Memory
NI 656x	PCI, PXI	400 Mb/s	LVDS	16	128 Mb/ch
NI 655x	PCI, PXI	100 Mb/s	Programmable -2.0 to 5.5 V	20	64 Mb/ch
NI 654x	PCI, PXI	100 Mb/s	5.0, 3.3, 2.5, 1.8 V	32	64 Mb/ch
NI 653x	PCI, PCIe, PXI, PXIe, PCMCIA	50 Mb/s	2.5, 3.3 V (5 V compatible)	32	32 Mb/ch

For applications requiring voltage levels beyond 5 V, such as 24 V logic, NI Industrial Digital I/O boards offer the widest range of signal compatibility. These low-cost devices feature isolated high-voltage channels capable of interfacing directly with many industrial actuators and sensors. In addition, Industrial Digital I/O devices complement HSDIO ATE solutions with lower-speed, software-timed digital logic. Refer to the related links below for more information.

Related Links

• Create, Edit, and Play Digital Waveforms with Real-Time Bit Comparison
• Why Should I Use National Instruments High-Speed Digital I/O?
• National Instruments High-Speed ATE and Stimulus Response Features
• Industrial Digital I/O

Digital I/O for Industrial Control and Automation

Industrial applications often involve requirements beyond the capabilities of a typical measurement device. For example, many industrial sensors and actuators require 24 V logic levels and may operate at different voltage potentials that can cause ground loops. Safety for the measurement or control system and safety for the user or operator are equally important. With voltage levels up to 150 V, high current drive, and isolation, NI Industrial Digital I/O devices can connect directly to a wide array of industrial pumps, valves, motors, and other sensors/actuators while providing a high degree of safety and reliability.

Figure 3. Industrial measurements with 24 V logic levels and isolation

These low-cost devices are ideal for industrial control and manufacturing test systems such as factory automation, embedded machine control, and production line verification. Furthermore, NI Industrial Digital I/O devices deliver a high-reliability industrial feature set designed to automate even the most demanding applications:

Industrial DIO is part of the Industrial DAQ suite of products that includes Industrial M and S Series multifunction boards. These devices complement the NI programmable automation controller (PAC) platform, providing industrial I/O that integrates seamlessly with logic, motion, process control, and vision applications. NI PACs combine PLC ruggedness with PC functionality under an open, flexible software architecture. Using LabVIEW, PACs with industrial DAQ and digital I/O can interface with existing PLC control applications to add more advanced functionality into industrial machines and improve efficiency.

Click here to learn how Innoventor integrated Industrial Digital I/O, Motion, and Vision to automate a beverage packaging system.

Read more about the industrial feature set here. The following table summarizes National Instrument’s Industrial Digital I/O offering.

For industrial control applications requiring custom or very precise timing and synchronization, R Series Intelligent DAQ devices combined with the cRIO-9151 R Series expansion chassis provide the ultimate in flexibility.

Figure 4. R Series Intelligent DAQ with NI cRIO-8151 signal conditioning

The NI cRIO-9151 connects directly to any digital connector of all PXI/PCI R Series devices and houses up to four C Series I/O modules for high-performance, industrial signal conditioning and screw terminal, BNC, or D-Sub connectivity. Refer to the R Series Intelligent DAQ Frequently Asked Questions document for more information.

Related Links

• Highest-Reliability Digital I/O at the Lowest Cost 
• Developing Measurement and Control Applications with the LabVIEW FPGA Module and Reconfigurable I/O Devices 
• FPGA-Based Control: Millions of Transistors at Your Command (FAQ) 

Digital I/O for Design and Prototyping

Design is an inherently iterative process. No matter the scope of the application, every design cycle proceeds from definition to simulation, prototyping, and testing; and more often than not these stages are repeated throughout progressive revisions. Having the means to alternate quickly between stages is paramount in optimizing the design process. Graphical system design with NI LabVIEW facilitates this need with a single platform encompassing the entire design cycle. Furthermore, digital R Series Intelligent DAQ combined with the LabVIEW FPGA Module offers unmatched hardware and software flexibility for design, prototyping, and deployment.

Intelligent DAQ features user-defined, onboard FPGA processing for complete control of system timing and triggering. You can configure the FPGA chip without any prior VHDL experience by creating LabVIEW block diagrams with the LabVIEW FPGA Module, giving you direct, immediate control over all the I/O. This process delivers high-performance, user-configurable timing and synchronization, as well as onboard decision making at rates up to 40 MHz.

For example, engineers developing applications using unsupported or custom digital communication protocols can use the LabVIEW FPGA module to quickly implement or prototype different communication interfaces on the FPGA-based R Series Intelligent DAQ hardware.

Figure 5. Custom digital protocols with R Series Intellignet DAQ and LabVIEW FPGA

Using LabVIEW FPGA, you can program each device’s “personality.” A personality is essentially a complied bitfile containing configuration information that is downloaded to the onboard FPGA. Rather than use a device with a fixed-personality or application-specific integrated circuit (ASIC), you have the ability to customize your board. Changing personalities as you proceed through the various iterations of a design cycle or prototype is as simple as modifying a LabVIEW block diagram and recompiling it. Once a personality is complete, LabVIEW FPGA is no longer required as the device may be accessed through LabVIEW for Windows or LabVIEW Real-Time. For more information on Custom DAQ personalities see the related links below or click here.

Click here  to learn how Micronova created an innovative HIL solution based on FPGAs for a 12 cylinder fuel injector simulator.

Intelligent DAQ offers up to 160 digital lines that may be individually configured for input, output, counter/timer, pulse-width modulation, and more. The following table summarizes National Instrument’s Intelligent DAQ offering.

Family	Bus	FPGA Size	DIO	Analog Inputs	Analog Outputs
Multifunction 783xR	PCI, PXI	1-3 M	56-96	4-8	4-8
Digital 781xR	PCI, PXI	1-3 M	160	-	-

NI High-Speed Digital I/O devices offer another option for many common tests involved in the design of digital devices. For applications requiring high-speed stimulus-response tests or non-standard voltage levels, for example, NI HSDIO devices complement Intelligent DAQ boards in the design cycle. HSDIO devices can also interface with higher-speed devices, transferring data at rates up to 400 Mb/s. Refer to the related links below for more information.

Related Links

 

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