Building Programmable Automation Controllers with LabVIEW
FPGA
Overview
Programmable Automation Controllers (PACs) are gaining acceptance within the
industrial control market as the ideal solution for applications that require highly integrated
analog and digital I/O, floating-point processing, and seamless connectivity to multiple
processing nodes. National Instruments offers a variety of PAC solutions powered by one
common software development environment, NI LabVIEW. With LabVIEW, you can build
custom I/O interfaces for industrial applications using add-on software, such as the NI
LabVIEW FPGA Module.
With the LabVIEW FPGA Module and reconfigurable I/O (RIO) hardware, National
Instruments delivers an intuitive, accessible solution for incorporating the flexibility and
customizability of FPGA technology into industrial PAC systems. You can define the logic
embedded in FPGA chips across the family of RIO hardware targets without knowing low-
level hardware description languages (HDLs) or board-level hardware design details, as well
as quickly define hardware for ultrahigh-speed control, customized timing and
synchronization, low-level signal processing, and custom I/O with analog, digital, and
counters within a single device. You also can integrate your custom NI RIO hardware with
image acquisition and analysis, motion control, and industrial protocols, such as CAN and
RS232, to rapidly prototype and implement a complete PAC system.
Table of Contents
1. Introduction
2. NI RIO Hardware for PACs
3. Building PACs with LabVIEW and the LabVIEW FPGA Module
4. FPGA Development Flow
5. Using NI SoftMotion to Create Custom Motion Controllers
6. Applications
7. Conclusion
Introduction
You can use graphical programming in LabVIEW and the LabVIEW FPGA Module to
configure the FPGA (field-programmable gate array) on NI RIO devices. RIO technology, the
merging of LabVIEW graphical programming with FPGAs on NI RIO hardware, provides a
flexible platform for creating sophisticated measurement and control systems that you could
previously create only with custom-designed hardware.
An FPGA is a chip that consists of many unconfigured logic gates. Unlike the fixed,
vendor-defined functionality of an ASIC (application-specific integrated circuit) chip, you can
configure and reconfigure the logic on FPGAs for your specific application. FPGAs are used
in applications where either the cost of developing and fabricating an ASIC is prohibitive, or
the hardware must be reconfigured after being placed into service. The flexible, software-
programmable architecture of FPGAs offer benefits such as high-performance execution of
custom algorithms, precise timing and synchronization, rapid decision making, and
simultaneous execution of parallel tasks. Today, FPGAs appear in such devices as
instruments, consumer electronics, automobiles, aircraft, copy machines, and application-
specific computer hardware. While FPGAs are often used in industrial control products,
FPGA functionality has not previously been made accessible to industrial control engineers.
Defining FPGAs has historically required expertise using HDL programming or complex
design tools used more by hardware design engineers than by control engineers.
With the LabVIEW FPGA Module and NI RIO hardware, you now can use LabVIEW, a
high-level graphical development environment designed specifically for measurement and
control applications, to create PACs that have the customization, flexibility, and high-
performance of FPGAs. Because the LabVIEW FPGA Module configures custom circuitry in
hardware, your system can process and generate synchronized analog and digital signals
rapidly and deterministically. Figure 1 illustrates many of the NI RIO devices that you can
configure using the LabVIEW FPGA Module.
Figure 1. LabVIEW FPGA VI Block Diagram and RIO Hardware Platforms
NI RIO Hardware for PACs
Historically, programming FPGAs has been limited to engineers who have in-depth
knowledge of VHDL or other low-level design tools, which require overcoming a very steep
learning curve. With the LabVIEW FPGA Module, NI has opened FPGA technology to a
broader set of engineers who can now define FPGA logic using LabVIEW graphical
development. Measurement and control engineers can focus primarily on their test and control
application, where their expertise lies, rather than the low-level semantics of transferring logic
into the cells of the chip. The LabVIEW FPGA Module model works because of the tight
integration between the LabVIEW FPGA Module and the commercial off-the-shelf (COTS)
hardware architecture of the FPGA and surrounding I/O components.
National Instruments PACs provide modular, off-the-shelf platforms for your industrial
control applications. With the implementation of RIO technology on PCI, PXI, and Compact
Vision System platforms and the introduction of RIO-based CompactRIO, engineers now
have the benefits of a COTS platform with the high-performance, flexibility, and
customization benefits of FPGAs at their disposal to build PACs. National Instruments PCI
and PXI R Series plug-in devices provide analog and digital data acquisition and control for
high-performance, user-configurable timing and synchronization, as well as onboard decision
making on a single device. Using these off-the-shelf devices, you can extend your NI PXI or
PCI industrial control system to include high-speed discrete and analog control, custom sensor
interfaces, and precise timing and control.
NI CompactRIO, a platform centered on RIO technology, provides a small, industrially
rugged, modular PAC platform that gives you high-performance I/O and unprecedented
flexibility in system timing. You can use NI CompactRIO to build an embedded system for
applications such as in-vehicle data acquisition, mobile NVH testing, and embedded machine
control systems. The rugged NI CompactRIO system is industrially rated and certified, and it
is designed for greater than 50 g of shock at a temperature range of -40 to 70 °C.
NI Compact Vision System is a rugged machine vision package that withstands the harsh
environments common in robotics, automated test, and industrial inspection systems. NI
CVS-145x devices offer unprecedented I/O capabilities and network connectivity for
distributed machine vision applications.NI CVS-145x systems use IEEE 1394 (FireWire)
technology, compatible with more than 40 cameras with a wide range of functionality,
performance, and price. NI CVS-1455 and NI CVS-1456 devices contain configurable
FPGAs so you can implement custom counters, timing, or motor control in your machine
vision application.
Building PACs with LabVIEW and the LabVIEW FPGA Module
With LabVIEW and the LabVIEW FPGA Module, you add significant flexibility and
customization to your industrial control hardware. Because many PACs are already
programmed using LabVIEW, programming FPGAs with LabVIEW is easy because it uses
the same LabVIEW development environment. When you target the FPGA on an NI RIO
device, LabVIEW displays only the functions that can be implemented in the FPGA, further
easing the use of LabVIEW to program FPGAs. The LabVIEW FPGA Module Functions
palette includes typical LabVIEW structures and functions, such as While Loops, For Loops,
Case Structures, and Sequence Structures as well as a dedicated set of LabVIEW FPGA-
specific functions for math, signal generation and analysis, linear and nonlinear control,
comparison logic, array and cluster manipulation, occurrences, analog and digital I/O, and
timing. You can use a combination of these functions to define logic and embed intelligence
onto your NI RIO device.
Figure 2 shows an FPGA application that implements a PID control algorithm on the NI
RIO hardware and a host application on a Windows machine or an RT target that
communicates with the NI RIO hardware. This application reads from analog input 0 (AI0),
performs the PID calculation, and outputs the resulting data on analog output 0 (AO0). While
the FPGA clock runs at 40 MHz the loop in this example runs much slower because each
component takes longer than one-clock cycle to execute. Analog control loops can run on an
FPGA at a rate of about 200 kHz. You can specify the clock rate at compile time. This
example shows only one PID loop; however, creating additional functionality on the NI RIO
device is merely a matter of adding another While Loop. Unlike traditional PC processors,
FPGAs are parallel processors. Adding additional loops to your application does not affect the
performance of your PID loop.
Figure 2. PID Control Using an Embedded LabVIEW FPGA VI with Corresponding LabVIEW Host
VI.
FPGA Development Flow
After you create the LabVIEW FPGA VI, you compile the code to run on the NI RIO
hardware. Depending on the complexity of your code and the specifications of your
development system, compile time for an FPGA VI can range from minutes to several hours.
