Reconfigurable I/O
NI 781x R User Manual
Reconfigurable I/O Devices for PCI and PXI/CompactPCI Bus Computers
NI 781xR User Manual
June 2006
371089D-01
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Contents
About This Manual
Conventions ...................................................................................................................vii
Reconfigurable I/O Documentation...............................................................................viii
Related Documentation..................................................................................................ix
Chapter 1
Introduction
About the Reconfigurable I/O Devices..........................................................................1-1
Using PXI with CompactPCI.........................................................................................1-2
Overview of Reconfigurable I/O ...................................................................................1-3
Reconfigurable I/O Concept............................................................................1-3
Reconfigurable I/O Architecture .....................................................................1-4
Reconfigurable I/O Applications.....................................................................1-5
Software Development ..................................................................................................1-5
LabVIEW FPGA Module................................................................................1-5
LabVIEW Real-Time Module .........................................................................1-6
Cables and Optional Equipment ....................................................................................1-7
Custom Cabling .............................................................................................................1-7
Safety Information .........................................................................................................1-8
Flexible Functionality .......................................................................1-3
User-Defined I/O Resources .............................................................1-4
Device-Embedded Logic and Processing .........................................1-4
Chapter 2
Hardware Overview of the NI 781x R
NI 7811R Overview.......................................................................................................2-2
NI 7813R Overview.......................................................................................................2-2
Digital I/O ......................................................................................................................2-2
Connecting Digital I/O Signals......................................................................................2-2
RTSI Trigger Bus...........................................................................................................2-4
PXI Local Bus................................................................................................................2-5
Switch Settings ..............................................................................................................2-6
Power Connections ........................................................................................................2-9
Appendix A
Specifications
© National Instruments Corporation v NI 781xR User Manual
Contents
Appendix B
Connecting I/O Signals
Appendix C
Using the SCB-68 Shielded Connector Block
Appendix D
Technical Support and Professional Services
Glossary
NI 781xR User Manual vi ni.com
About This Manual
This manual describes the electrical and mechanical aspects of the
National Instruments 781xR devices, and contains information about
programming and using the devices.
Conventions
The following conventions appear in this manual:
<> Angle brackets that contain numbers separated by an ellipsis represent a
range of values associated with a bit or signal name—for example,
AO <3..0> .
» The » symbol leads you through nested menu items and dialog box options
to a final action. The sequence File»Page Setup»Options directs you to
pull down the File menu, select the Page Setup item, and select Options
from the last dialog box.
This icon denotes a note, which alerts you to important information.
This icon denotes a caution, which advises you of precautions to take to
avoid injury, data loss, or a system crash. When this symbol is marked on
the device, refer to the Safety Information section of Chapter 1,
Introduction, for precautions to take.
bold Bold text denotes items that you must select or click in the software, such
as menu items and dialog box options. Bold text also denotes parameter
names and hardware labels.
italic Italic text denotes variables, emphasis, a cross-reference, or an introduction
to a key concept. Italic text also denotes text that is a placeholder for a word
or value that you must supply.
© National Instruments Corporation vii NI 781xR User Manual
About This Manual
monospace Text in this font denotes text or characters that you should enter from the
keyboard, sections of code, programming examples, and syntax examples.
This font is also used for the proper names of disk drives, paths, directories,
programs, subprograms, subroutines, device names, functions, operations,
variables, filenames, and extensions.
NI 781xRNI781xR refers to all R Series devices with digital I/O.
Reconfigurable I/O Documentation
The NI 781xR User Manual is one piece of the documentation set for your
reconfigurable I/O system and application. Depending on the hardware and
software you use for your application, you could have any of several types
of documentation. The documentation set includes the following
documents:
• Getting Started with the NI 781xR—This document lists what you
need to get started, describes how to unpack and install the software
and hardware, and contains information about connecting I/O signals
to the NI 781xR.
• LabVIEW FPGA Module Release and Upgrade Notes—This
document contains information about installing and getting started
with the LabVIEW FPGA Module. Select Start»Program Files»
National Instruments»<LabVIEW>»LabVIEW Manuals to view
the LabVIEW Manuals directory that contains this document.
• LabVIEW Help—Select Help»Search the LabVIEW Help in
LabVIEW to view the LabVIEW Help. This help file contains
information about using VIs with the NI 781xR and using the
LabVIEW FPGA Module and the LabVIEW Real-Time Module.
– Browse the FPGA Module book in the Contents tab for
information about how to use the FPGA Module to create VIs that
run on the NI 781xR device.
– Browse the Real-Time Module book in the Contents tab for
information about how to build deterministic applications using
the LabVIEW Real-Time Module.
NI 781xR User Manual viii ni.com
Related Documentation
The following documents contain information you may find helpful:
• PICMG CompactPCI 2.0 R3.0
• PXI Hardware Specification Revision 2.1
• PXI Software Specification Revision 2.1
• PCI Specification Revision 3.0
About This Manual
© National Instruments Corporation ix NI 781xR User Manual
Introduction
This chapter describes the NI 781xR, the concept of the Reconfigurable I/O
(RIO) device, optional software and equipment for using the NI 781xR, and
safety information about the NI 781xR.
About the Reconfigurable I/O Devices
The NI 781xR devices are R Series RIO devices with 160 digital I/O (DIO)
lines and four DIO connectors.
• The NI 7811R has a one million gate Field-Programmable Gate Array
(FPGA).
• The NI 7813R has a three million gate FPGA.
A user-reconfigurable FPGA controls the digital I/O lines on the NI 781xR.
The FPGA on the R Series device allows you to define the functionality and
timing of the device. You can change the functionality of the FPGA on the
R Series device in LabVIEW using the LabVIEW FPGA Module to create
and download a custom virtual instrument (VI) to the FPGA. Using the
FPGA Module, you can graphically design the timing and functionality of
the R Series device. If you have LabVIEW but not the FPGA Module, you
cannot create new FPGA VIs, but you can create VIs that run on Windows
or on a LabVIEW Real-Time (RT) target to control existing FPGA VIs.
1
Some applications require tasks such as real-time, floating-point
processing, or datalogging while performing I/O and logic on the R Series
device. You can use the LabVIEW Real-Time Module to perform these
additional applications while communicating with and controlling the
R Series device.
The R Series device contains flash memory to store a startup VI for
automatic loading of the FPGA when the system is powered on.
The NI 781xR uses the Real-Time System Integration (RTSI) bus to easily
synchronize several measurement functions to a common trigger or timing
event. The NI 781xR accesses the RTSI bus through the PXI trigger lines
implemented on the PXI backplane. The RTSI bus can route timing and
trigger signals between as many as seven PXI devices in your system.
© National Instruments Corporation 1-1 NI 781xR User Manual
Chapter 1 Introduction
You can add additional I/O channels and signal conditioning using the
CompactRIO R Series Expansion Chassis and CompactRIO I/O modules.
Refer to Appendix A, Specifications, for detailed NI 781xR specifications.
Using PXI with CompactPCI
Using PXI-compatible products with standard CompactPCI products is an
important feature provided by PXI Hardware Specification Revision 2.1
and PXI Software Specification Revision 2.1. If you use a PXI-compatible
plug-in card in a standard CompactPCI chassis, you cannot use
PXI-specific functions, but you still can use the basic plug-in card
functions. For example, the RTSI bus on the R Series device is available in
a PXI chassis, but not in a CompactPCI chassis.
The CompactPCI specification permits vendors to develop sub-buses that
coexist with the basic PCI interface on the CompactPCI bus. Compatible
operation is not guaranteed between CompactPCI devices with different
sub-buses nor between CompactPCI devices with sub-buses and PXI.
The standard implementation for CompactPCI does not include these
sub-buses. The R Series device works in any standard CompactPCI chassis
adhering to the PICMG CompactPCI 2.0 R3.0 core specification.
PXI-specific features are implemented on the J2 connector of the
CompactPCI bus. Table 1-1 lists the J2 pins used by the NI PXI-781xR.
The NI PXI-781xR is compatible with any CompactPCI chassis with a
sub-bus that does not drive these lines. Even if the sub-bus is capable of
driving these lines, the R Series device is still compatible as long as those
pins on the sub-bus are disabled by default and are never enabled.
Caution Damage can result if the J2 lines are driven by the sub-bus.
NI 781xR User Manual 1-2 ni.com
Chapter 1 Introduction
Table 1-1. Pins Used by the NI PXI-781xR
NI PXI-781xR Signal PXI Pin Name PXI J2 Pin Number
PXI Trigger<0..7> PXI Trigger<0..7> A16, A17, A18, B16, B18, C18,
E16, E18
PXI Clock 10 MHz PXI Clock 10 MHz E17
PXI Star Trigger PXI Star Trigger D17
LBLSTAR<0..12> LBL<0..12> A1, A19, C1, C19, C20, D1, D2,
D15, D19, E1, E2, E19, E20
LBR<0..12> LBR<0..12> A2, A3, A20, A21, B2, B20, C3,
C21, D3, D21, E3, E15, E21
Overview of Reconfigurable I/O
This section explains reconfigurable I/O and describes how to use the
LabVIEW FPGA Module to build high-level functions in hardware.
Refer to Chapter 2, Hardware Overview of the NI 781x R, for descriptions
of the I/O resources on the NI 781xR.
Reconfigurable I/O Concept
The NI 781xR is based on a reconfigurable FPGA core surrounded by fixed
digital input and output resources. You can configure the behavior of the
FPGA to meet the requirements of your measurement and control system.
You can implement this user-defined behavior as an FPGA VI to create an
application-specific I/O device.
Flexible Functionality
Flexible functionality allows the NI 781xR to match individual application
requirements and to mimic the functionality of fixed I/O devices. For
example, you can configure an R Series device in one application for three
32-bit quadrature encoders and then reconfigure the R Series device in
another application for eight 16-bit event counters.
You also can use the R Series device with the LabVIEW Real-Time
Module in timing and triggering applications, such as control and
hardware-in-the-loop (HIL) simulations. For example, you can configure
the R Series device for a single timed loop in one application and then
© National Instruments Corporation 1-3 NI 781xR User Manual
Chapter 1 Introduction
reconfigure the device in another application for four independent timed
loops with separate I/O resources.
User-Defined I/O Resources
You can create your own custom measurements using the fixed I/O
resources. For example, one application might require an event counter that
increments when a rising edge appears on any of three digital input lines.
You can implement these behaviors in the hardware for fast, deterministic
performance.
Device-Embedded Logic and Processing
You can implement LabVIEW logic and processing on the FPGA of the
R Series device. Typical logic functions include Boolean operations,
comparisons, and basic mathematical operations. You can implement
multiple functions efficiently in the same design, operating sequentially or
in parallel. You also can implement more complex algorithms such as
control loops. You are limited only by the size of the FPGA.
Reconfigurable I/O Architecture
Figure 1-1 shows an FPGA connected to fixed I/O resources and a bus
interface.
Fixed I/O Resource
Fixed I/O Resource
FPGA
Bus Interface
Figure 1-1. High-Level FPGA Functional Overview
NI 781xR User Manual 1-4 ni.com
Fixed I/O Resource
Fixed I/O Resource
Chapter 1 Introduction
Software accesses the R Series device through the bus interface. The FPGA
connects the bus interface and the fixed I/O to make possible timing,
triggering, processing, and custom I/O measurements using the LabVIEW
FPGA Module.
The FPGA logic provides timing, triggering, processing, and custom I/O
measurements. Each fixed I/O resource used by the application uses a small
portion of the FPGA logic that controls the fixed I/O resource. The bus
interface also uses a small portion of the FPGA logic to provide software
access to the device.
The remaining FPGA logic is available for higher-level functions such as
timing, triggering, and counting. The functions use varied amounts of logic.
You can place useful applications in the FPGA. How much FPGA space
your application requires depends on your need for I/O recovery, I/O, and
logic algorithms.
The FPGA does not retain the VI when the R Series device is powered off,
so you must reload the VI every time you power on the device. You can load
the VI from onboard flash memory or from software over the bus interface.
One advantage to using flash memory is that the VI can start executing
almost immediately after power-up instead of waiting for the computer to
completely boot and load the FPGA VI. Refer to the LabVIEW Help for
more information about how to store your VI in flash memory.
Reconfigurable I/O Applications
You can use the LabVIEW FPGA Module to create or acquire new VIs for
your application. The FPGA Module allows you to define custom
functionality for the R Series device using a subset of LabVIEW
functionality. Refer to the R Series examples, located in the
examples\R Series
directory, for examples of FPGA VIs.
<LabVIEW>\
Software Development
You can use LabVIEW with the LabVIEW FPGA Module to program the
NI 781xR. To develop real-time applications that control the NI 781xR, use
LabVIEW with the LabVIEW Real-Time Module.
LabVIEW FPGA Module
The LabVIEW FPGA Module enables you to use LabVIEW to create VIs
that run on the FPGA of the R Series device. Use the FPGA Module VIs
© National Instruments Corporation 1-5 NI 781xR User Manual
Chapter 1 Introduction
Note If you use the R Series device without the FPGA Module, you can use the RIO
Device Setup utility, available by selecting Start»Program Files»National Instruments»
NI-RIO»RIO Device Setup, to download precompiled FPGA VIs to the flash memory of
the R Series device. This utility is installed by the NI-RIO CD. You also can use the utility
to synchronize the clock R Series device to the PXI clock, and to configure when the VI
loads from flash memory.
and functions to control the I/O, timing, and logic of the R Series device
and generate interrupts for synchronization. Select Help»Search the
LabVIEW Help to view th e LabVIEW Help. In the LabVIEW Help, use the
Contents tab to browse to the FPGA Interface book for more information
about the FPGA Interface functions.
You can use Interactive Front Panel Communication to communicate
directly with the FPGA VI running on the FPGA target. You can use
Programmatic FPGA Interface Communication to programmatically
monitor and control an FPGA VI with a separate host VI.
Use the FPGA Interface functions when you target LabVIEW for Windows
or an RT target to create host VIs that wait for interrupts and control the
FPGA by reading and writing to the FPGA VI running on the R Series
device.
LabVIEW Real-Time Module
The LabVIEW Real-Time Module extends the LabVIEW development
environment to deliver deterministic, real-time performance.
You can write host VIs that run in Windows or on RT targets to
communicate with FPGA VIs that run on the NI 781xR.You can develop
real-time VIs with LabVIEW and the LabVIEW Real-Time Module and
then download the Real-Time VIs to run on a hardware target with a
real-time operating system. The LabVIEW Real-Time Module allows you
to use the NI 781xR in RT Series PXI systems being controlled in real time
by a VI.
The NI 781xR is designed as a single-point DIO complement to
the LabVIEW Real-Time Module. Refer to the LabVIEW Help, available
by selecting Help»Search the LabVIEW Help, for more information
about the LabVIEW Real-Time Module.
NI 781xR User Manual 1-6 ni.com
Cables and Optional Equipment
National Instruments offers a variety of products you can use with R Series
devices, including cables, connector blocks, and other accessories listed in
Table 1-2.
Table 1-2. Cables and Accessories
Cable Cable Description Accessories
Chapter 1 Introduction
SH68-C68-S Shielded 68-pin VHDCI male
connector to female 0.050 series
D-type connector. The cable is
constructed with 34 twisted wire
pairs plus an overall shield.
NSC68-5050 Unshielded cable connects from
68-pin VHDCI male connector to
two 50-pin female headers. The
pinout of these headers allows for
direct connection to SSR
backplanes for digital signal
conditioning.
Refer to Appendix B, Connecting I/O Signals, for more information about
using these cables and accessories to connect I/O signals to the NI 781xR.
Refer to
the most current cabling options.
ni.com/products or contact the sales office nearest to you for
Custom Cabling
Connects to the following standard
68-pin screw-terminal blocks:
• SCB-68
• CB-68LP
• CB-68LPR
•TBX-68
• cRIO-9151—passive backplane
50-pin headers can connect to the
following SSR backplanes for digital
signal conditioning:
• 8-channel backplane
• 16-channel backplane
• 32-channel backplane
NI offers a variety of cables for connecting signals to the NI 781xR. If you
need to develop a custom cable, a generic unterminated shielded cable is
available from NI. The SHC68-NT-S connects to the NI 781xR VHDCI
connectors on one end of the cable. The other end of the cable is not
terminated. This cable ships with a wire list identifying which wire
corresponds to each NI 781xR pin. Using this cable, you can quickly
connect the NI 781xR signals that you need to the connector of your choice.
Refer to Appendix B, Connecting I/O Signals, for the NI 781xR connector
pinouts.
© National Instruments Corporation 1-7 NI 781xR User Manual
Chapter 1 Introduction
Safety Information
The following section contains important safety information that you must
follow when installing and using the NI 781xR.
Do not operate the NI 781xR in a manner not specified in this document.
Misuse of the NI 781xR can result in a hazard. You can compromise the
safety protection built into the NI 781xR if the NI 781xR is damaged in any
way. If the NI 781xR is damaged, return it to NI for repair.
Do not substitute parts or modify the NI 781xR except as described in this
document. Use the NI 781xR only with the chassis, modules, accessories,
and cables specified in the installation instructions. You must have all
covers and filler panels installed during operation of the NI 781xR.
Do not operate the NI 781xR in an explosive atmosphere or where there
might be flammable gases or fumes. If you must operate the NI 781xR in
such an environment, it must be in a suitably rated enclosure.
If you need to clean the NI 781xR, use a soft, nonmetallic brush. Make sure
that the NI 781xR is completely dry and free from contaminants before
returning it to service.
Operate the NI 781xR only at or below Pollution Degree 2. Pollution is
foreign matter in a solid, liquid, or gaseous state that can reduce dielectric
strength or surface resistivity. The following list describes pollution
degrees:
• Pollution Degree 1—No pollution or only dry, nonconductive
pollution occurs. The pollution has no influence.
• Pollution Degree 2—Only nonconductive pollution occurs in most
cases. Occasionally, however, a temporary conductivity caused by
condensation must be expected.
• Pollution Degree 3—Conductive pollution occurs, or dry,
nonconductive pollution occurs that becomes conductive due to
condensation.
You must insulate signal connections for the maximum voltage for which
the NI 781xR is rated. Do not exceed the maximum ratings for the
NI 781xR. Do not install wiring while the NI 781xR is live with electrical
signals. Do not remove or add connector blocks when power is connected
to the system. Remove power from signal lines before connecting them to
or disconnecting them from the NI 781xR.
NI 781xR User Manual 1-8 ni.com
Chapter 1 Introduction
Operate the NI 781xR at or below the measurement category1 listed in the
Environmental section of Appendix A, Specifications. Measurement
circuits are subjected to working voltages
2
and transient stresses
(overvoltage) from the circuit to which they are connected during
measurement or test. Measurement categories establish standard impulse
withstand voltage levels that commonly occur in electrical distribution
systems. The following list describes installation categories:
• Measurement Category I—Measurements performed on circuits not
directly connected to the electrical distribution system referred to as
MAINS
3
voltage. This category is for measurements of voltages from
specially protected secondary circuits. Such voltage measurements
include signal levels, special equipment, limited-energy parts of
equipment, circuits powered by regulated low-voltage sources, and
electronics.
• Measurement Category II—Measurements performed on circuits
directly connected to the electrical distribution system. This category
refers to local-level electrical distribution, such as that provided by a
standard wall outlet (for example, 115 V for U.S. or 230 V for Europe).
Examples of Measurement Category II are measurements performed
on household appliances, portable tools, and similar products.
• Measurement Category III—Measurements performed in the
building installation at the distribution level. This category refers to
measurements on hard-wired equipment such as equipment in fixed
installations, distribution boards, and circuit breakers. Other examples
are wiring, including cables, bus-bars, junction boxes, switches,
socket-outlets in the fixed installation, and stationary motors with
permanent connections to fixed installations.
• Measurement Category IV—Measurements performed at the
primary electrical supply installation (<1,000 V). Examples include
electricity meters and measurements on primary overcurrent
protection devices and on ripple control units.
1
Measurement categories, also referred to as installation categories, are defined in electrical safety standard IEC 61010-1.
2
Working voltage is the highest rms value of an AC or DC voltage that can occur across any particular insulation.
3
MAINS is defined as a hazardous live electrical supply system that powers equipment. Suitably rated measuring circuits may
be connected to the MAINS for measuring purposes.
© National Instruments Corporation 1-9 NI 781xR User Manual
Hardware Overview
of the NI 781x R
This chapter presents an overview of the hardware functions and
I/O connectors on the NI 781xR.
Figure 2-1 shows a block diagram for the NI 781xR.
2
Digital I/O (40)
Connector 0 (DIO)Connector 1 (DIO)Connector 2 (DIO)Connector 3 (DIO)
Digital I/O (40)
Digital I/O (40)
Digital I/O (40)
User-Configurable
FPGA on
RIO Devices
Configuration Control
Configuration
Data/Address/Control
PXI Local Bus (NI PXI-781x R Only)
RTSI Bus
Flash Memory
Bus
Interface
Control
Address/Data
PCI/PXI/CompactPCI Bus
RTSI/PXI Triggers
Figure 2-1. NI 781xR Block Diagram
© National Instruments Corporation 2-1 NI 781xR User Manual
Chapter 2 Hardware Overview of the NI 781xR
NI 7811R Overview
The NI 7811R has 160 bidirectional DIO lines and a one million gate
FPGA.
NI 7813R Overview
The NI 7813R has 160 bidirectional DIO lines and a three million gate
FPGA.
Digital I/O
You can configure the NI 781xR DIO lines individually for either input or
output. When the system powers on, the DIO lines are all high-impedance.
To set another power-on state, you can configure the NI 781xR to load a VI
when the system powers on. This VI then can then set the DIO lines to any
power-on state.
Connecting Digital I/O Signals
The DIO signals on the NI 781xR connectors are DGND and DIO<0..39>.
DIO<0..n> signals make up the DIO port, and DGND is the ground
reference signal for the DIO port. The NI 781xR has four DIO connectors
for a total of 160 DIO lines.
Refer to Figure B-1, NI 781xR Connector Locations, and Figure B-2,
NI 781x R I/O Connector Pin Assignments, for the connector locations and
the I/O connector pin assignments on the NI 781xR.
The DIO lines on the NI 781xR are TTL compatible. When configured as
inputs, they can receive signals from 5 V TTL, 3.3 V LVTTL, 5 V CMOS,
and 3.3 V LVCMOS devices. When configured as outputs, they can send
signals to 5 V TTL, 3.3 V LVTTL, and 3.3 V LVCMOS devices. Because
the digital outputs provide a nominal output swing of 0 to 3.3 V
(3.3 V TTL), the DIO lines cannot drive 5 V CMOS logic levels. To
interface to 5 V CMOS devices, you must provide an external pull-up
resistor to 5 V. This resistor pulls up the 3.3 V digital output from the
NI 781xR to 5 V CMOS logic levels. Refer to Appendix A, Specifications,
for detailed DIO specifications.
NI 781xR User Manual 2-2 ni.com
Chapter 2 Hardware Overview of the NI 781xR
Caution Exceeding the maximum input voltage ratings listed in Table B-2, NI 781xR I/O
Signal Summary, can damage the NI 781xR and the computer. NI is not liable for any
damage resulting from such signal connections.
Caution Do not short the DIO lines of the NI 781xR directly to power or to ground. Doing
so can damage the NI 781xR by causing excessive current to flow through the DIO lines.
You can connect multiple NI 781xR digital output lines in parallel to
provide higher current sourcing or sinking capability. If you connect
multiple digital output lines in parallel, your application must drive all of
these lines simultaneously to the same value. If you connect digital lines
together and drive them to different values, excessive current can flow
through the DIO lines and damage the NI 781xR. Refer to Appendix A,
Specifications, for more information about DIO specifications. Figure 2-2
shows signal connections for three typical DIO applications.
LED
TTL or
5 V CMOS
DGND
†
+5 V
LVCMOS
Compatible
Devices
*
DIO<4..7>
TTL, LVTTL, CMOS, or LVCMOS Signal
+5 V
Switch
I/O Connector
*
3.3 V CMOS
†
Use a pull-up resistor when driving 5 V CMOS devices
DGND
DIO<0..3>
NI 781xR
Figure 2-2. Example Digital I/O Connections
© National Instruments Corporation 2-3 NI 781xR User Manual
Chapter 2 Hardware Overview of the NI 781xR
Figure 2-2 shows DIO<0..3> configured for digital input and DIO<4..7>
configured for digital output. Digital input applications include receiving
TTL, LVTTL, CMOS, or LVCMOS signals and sensing external device
states, such as the state of the switch shown in Figure 2-2. Digital output
applications include sending TTL or LVCMOS signals and driving external
devices, such as the LED shown in Figure 2-2.
The NI 781xR SH68-C68-S shielded cable contains 34 twisted pairs of
conductors. To maximize the digital I/O available on the NI 781xR, some
of the DIO lines are twisted with power or ground, and some DIO lines are
twisted with other DIO lines. To obtain maximum signal integrity, place
edge-sensitive or high-frequency digital signals on the DIO lines that are
paired with power or ground. Because the DIO lines that are twisted with
other DIO lines can couple noise onto each other, use these lines for static
signals or for non-edge-sensitive, low-frequency digital signals. Examples
of high-frequency or edge-sensitive signals include clock, trigger,
pulse-width modulation (PWM), encoder, and counter signals. Examples of
static signals or non-edge-sensitive, low-frequency signals include LEDs,
switches, and relays. Table 2-1 summarizes these guidelines.
Table 2-1. DIO Signal Guidelines for the NI PXI-781xR
SH68-C68-S Shielded
Digital Lines
DIO<0..27> DIO line paired with power
DIO<28..39> DIO line paired with another
Cable Signal Pairing
or ground
DIO line
RTSI Trigger Bus
The NI 781xR can send and receive triggers through the RTSI trigger bus.
The RTSI bus provides eight shared trigger lines that connect to all the
devices on the bus. In PXI, the trigger lines are shared between all the PXI
slots in a bus segment. In PCI, the RTSI bus is implemented through a
ribbon cable connected to the RTSI connector on each device that needs to
access the RTSI bus.
You can use the RTSI trigger lines to synchronize the NI 781xR to any other
device that supports RTSI triggers. On the NI PCI-781xR, the RTSI trigger
Recommended Types
of Digital Signals
All types—high-frequency or
low-frequency signals,
edge-sensitive or
non-edge-sensitive signals
Static signals or
non-edge-sensitive,
low-frequency signals
NI 781xR User Manual 2-4 ni.com
Chapter 2 Hardware Overview of the NI 781xR
lines are labeled RTSI/TRIG<0..6> and RTSI/OSC. On the NI PXI-781xR,
the RTSI trigger lines are labeled PXI/TRIG<0..7>. In addition, the
NI PXI-781xR can use the PXI star trigger line to send or receive triggers
from a device plugged into Slot 2 of the PXI chassis. The PXI star trigger
line on the NI PXI-781xR is PXI/STAR.
The NI 781xR can configure each RTSI trigger line as either an input or an
output signal. Because each trigger line on the RTSI bus is connected in
parallel to all the other RTSI devices on the bus, only one device should
drive a particular RTSI trigger line at a time. For example, if one
NI PXI-781xR is configured to send out a trigger pulse on PXI/TRIG0,
the remaining devices on that PXI bus segment must have PXI/TRIG0
configured as an input.
Caution Do not drive the same RTSI trigger bus line with the NI 781xR and another device
simultaneously. Such signal driving can damage both devices. NI is not liable for any
damage resulting from such signal driving.
For more information on using and configuring triggers, select
Help»Search the LabVIEW Help in LabVIEW to view the LabVIEW
Help. Refer to the PXI Hardware Specification Revision 2.1 and PXI
Software Specification Revision 2.1 at
information about PXI triggers.
www.pxisa.org for more
PXI Local Bus
The NI PXI-781xR can communicate with other PXI devices using the PXI
local bus. The PXI local bus is a daisy-chained bus that connects each PXI
peripheral slot with the adjacent peripheral slot on either side. For example,
the right local bus lines from a given PXI peripheral slot connect to the left
local bus lines of the adjacent slot on the right. Each local bus is 13 lines
wide. All of these lines connect to the FPGA on the NI PXI-781xR, and you
can use these lines as you use any of the other NI PXI-781xR DIO lines.
The PXI local bus right lines on the NI PXI-781xR are PXI/LBR<0..12>.
The PXI local bus left lines on the NI PXI-781xR are
PXI/LBLSTAR<0..12>.
The NI PXI-781xR can configure each PXI local bus line as either an input
or an output signal. Only one device can drive the same physical local bus
line at a given time. For example, if an NI PXI-781xR is configured to drive
a signal on PXI/LBR0, the device in the slot immediately to the right must
have its PXI/LBLSTAR 0 line configured as an input.
© National Instruments Corporation 2-5 NI 781xR User Manual
Chapter 2 Hardware Overview of the NI 781xR
Caution Do not drive the same PXI local bus line with the NI PXI-781xR and another
device simultaneously. Such signal driving can damage both devices. NI is not liable for
any damage resulting from such signal driving.
The NI PXI-781xR local bus lines are compatible only with 3.3 V signaling
LVTTL and LVCMOS levels.
Caution Do not enable the local bus lines on an adjacent device if the device drives
anything other than 0–3.3 V LVTTL signal levels on the NI PXI-781xR. Enabling the lines
in this way can damage the NI PXI-781xR. NI is not liable for any damage resulting from
enabling such lines.
The left local bus lines from the left peripheral slot of a PXI backplane
(Slot 2) are routed to the star trigger lines of up to 13 other peripheral slots
in a two-segment PXI system. This configuration provides a dedicated,
delay-matched trigger signal between the first peripheral slot and the
other peripheral slots and results in very precise trigger timing signals.
For example, an NI PXI-781xR in Slot 2 can send an independent
trigger signal to each device plugged into Slots <3..15> using the
PXI/LBLSTAR<0..12>. Each device receives its trigger signal on its own
dedicated star trigger line.
Caution Do not configure the NI PXI-781xR and another device to drive the same physical
star trigger line simultaneously. Such signal driving can damage the NI PXI-781xR and the
other device. NI is not liable for any damage resulting from such signal driving.
Refer to the PXI Hardware Specification Revision 2.1 and PXI Software
Specification Revision 2.1 at
www.pxisa.org for more information about
PXI triggers.
Switch Settings
Refer to Figure 2-3 for the location of the switches on the NI 781xR. For
normal operation, SW1 is in the OFF position. To prevent a VI stored in
flash memory from loading to the FPGA at power up, move SW1 to the
ON position, as shown in Figure 2-5.
Note SW2 and SW3 are not connected.
NI 781xR User Manual 2-6 ni.com
NI PXI-
7811R
Reconfigurable I/O
Chapter 2 Hardware Overview of the NI 781xR
SW1, SW2, SW3
CONNECTOR 3 (DIO)
CONNECTOR 2 (DIO)
Figure 2-3. Switch Location on the NI PXI-781xR
© National Instruments Corporation 2-7 NI 781xR User Manual
Chapter 2 Hardware Overview of the NI 781xR
SW1, SW2, SW3
Figure 2-4. Switch Location on the NI PCI-781xR
ON
123
a. Normal Operation (Default)
b. Prevent VI From Loading
ON
123
Figure 2-5. Switch Settings
NI 781xR User Manual 2-8 ni.com
Chapter 2 Hardware Overview of the NI 781xR
Complete the following steps to prevent a VI stored in flash memory from
loading to the FPGA:
1. Power off and unplug the PC or the PXI/CompactPCI chassis.
2. Remove the NI 781xR from the PCI or PXI/CompactPCI chassis.
3. Move SW1 to the ON position, as shown in Figure 2-5b.
4. Reinsert the NI PXI-781xR into the PC or PXI/CompactPCI chassis.
Refer to the Installing the Hardware section of the Getting Started
with the NI 781xR document for installation instructions.
5. Plug in and power on the PC or PXI/CompactPCI chassis.
After you complete this procedure, a VI stored in flash memory does not
load to the FPGA at power up. You can use software to reconfigure the
NI 781xR, if necessary. To return to the default setting so that VIs load from
flash memory, repeat the previous procedure but return SW1 to the OFF
position in step 3. You can use this switch to enable or disable the ability to
load from flash memory. In addition to this switch, you must configure the
NI 781xR with the software to autoload an FPGA VI.
Note When the NI 781xR is powered on with SW1 in the ON position, the analog circuitry
does not return properly calibrated data. Move the switch to the ON position only while
you are using software to reconfigure the NI 781xR for the desired power-up behavior.
Afterward, return SW1 to the OFF position.
Power Connections
Two pins on each I/O connector supply 5 V from the computer power
supply using a self-resetting fuse. The fuse resets automatically within a
few seconds after the overcurrent condition is removed. The +5 V pins are
referenced to DGND and power external digital circuitry. The NI 781xR
has the following power rating:
+4.50 to +5.25 VDC (250 mA max per 5 V pin)
Caution Do not connect the +5 V power pins directly to digital ground or to any other
voltage source on the NI 781xR or on any other device under any circumstance. Doing so
can damage the NI 781xR and the computer. NI is not liable for damage resulting from
such a connection.
© National Instruments Corporation 2-9 NI 781xR User Manual
Specifications
This appendix lists the specifications of the NI 781xR. These specifications
are typical at 25 °C unless otherwise noted.
Digital I/O
Number of channels ............................... 160 input/output
Compatibility ......................................... TTL
Digital logic levels
A
Level Min Max
Input low voltage (VIL)
Input high voltage (V
Output low voltage (VOL),
where I
Output high voltage (V
where I
Maximum output current
I
I
Input leakage current.............................. ±10 µA
Power-on state........................................ Programmable by line
Data transfers ......................................... Interrupts, programmed I/O
Protection
Input ................................................ –0.5 to 7.0 V
Output ............................................. Short-circuit (up to eight lines
= –I
OUT
= I
OUT
max
(sink) ........................................ 5.0 mA
max
(source) .................................... 5.0 mA
max
(sink)
max
(source)
)
IH
),
OH
can be shorted at a time)
0.0 V
2.0 V
—
2.4 V
0.8 V
5.5 V
0.4 V
—
© National Instruments Corporation A-1 NI 781xR User Manual
Appendix A Specifications
Reconfigurable FPGA
Number of logic slices
Equivalent number of logic cells
Available embedded RAM
Timebase.................................................40, 80, 120, 160, or 200 MHz
Timebase reference sources....................Onboard clock, phase-locked to
Timebase accuracy
NI 7811R .........................................5,120
NI 7813R .........................................14,336
NI 7811R .........................................11,520
NI 7813R .........................................32,256
NI 7811R .........................................81,920 bytes
NI 7813R .........................................196,608 bytes
PXI 10 MHz clock
Onboard clock .................................±100 ppm, 450 ps jitter
Phase locked to
PXI 10 MHz clock...........................Adds 350 ps jitter, 300 ps skew
Additional frequency-dependent jitter
40 MHz............................................None
80 MHz............................................400 ps
120 MHz..........................................720 ps
160 MHz..........................................710 ps
200 MHz..........................................700 ps
Bus Interface
NI 781xR.................................................Master, slave
NI 781xR User Manual A-2 ni.com
Power Requirement
Appendix A Specifications
+5 VDC (±5%)
NI 7811R......................................... 9 mA (typ), 50 mA (max)
NI 7813R......................................... 9 mA (typ), 50 mA (max)
1
1
+3.3 VDC (±5%)
NI 7811R......................................... 650 mA (typ), 1,000 mA (max)
NI 7813R......................................... 850 mA (typ), 1,350 mA (max)
To calculate the total current sourced by the digital outputs, use the
following equation:
j
current sourced on channel
∑
i 1=
i
where j is the number of digital outputs being used to source current.
Power available at I/O connectors ......... +4.50 to +5.25 VDC,
250 mA per I/O connector pin
2
2
Physical
Dimensions (not including connectors)
NI PXI-781xR ................................ 16.0 cm × 10.0 cm
(6.3 in. × 3.9 in.)
NI PCI-781xR ................................ 15.5 cm × 10.6 cm
(6.105 in. × 4.162 in.)
Weight
PCI-781xR ...................................... 112 g
PXI-781xR ...................................... 162 g
I/O connectors ........................................ Four 68-pin female high-density
VHDCI type
1
Does not include current drawn form the +5 V line on the I/O connectors.
2
Does not include current sourced by the digital outputs.
© National Instruments Corporation A-3 NI 781xR User Manual
Appendix A Specifications
Environmental
Operating Environment
The NI 781xR is intended for indoor use only.
Ambient temperature range ....................0 °C to 55 °C, tested in
accordance with IEC-60068-2-1
and IEC-60068-2-2
Relative humidity range..........................10% to 90%, noncondensing,
tested in accordance with
IEC-60068-2-56
Altitude ...................................................2,000 m at 25 °C ambient
temperature
Storage Environment
Ambient temperature range ....................–20 °C to 70 °C, tested in
accordance with IEC-60068-2-1
and IEC-60068-2-2
Relative humidity range..........................5% to 95%, noncondensing,
tested in accordance with
IEC-60068-2-56
Note Clean the device with a soft, non-metallic brush. Make sure that the device is
completely dry and free from contaminants before returning it to service.
Shock and Vibration (NI PXI-781x R Only)
Operational shock ...................................30 g peak, half-sine, 11 ms pulse
Tested in accordance with
IEC-60068-2-27. Test profile
developed in accordance with
MIL-PRF-28800F.
Random vibration
Operating .........................................5 Hz to 500 Hz, 0.3 g
Nonoperating ...................................5 Hz to 500 Hz, 2.4 g
Tested in accordance with
IEC-60068-2-64. Nonoperating
test profile exceeds the
requirements of
MIL-PRF-28800F, Class 3.
NI 781xR User Manual A-4 ni.com
rms
rms
Safety
The NI 781xR is designed to meet the requirements of the following
standards of safety for electrical equipment for measurement, control,
and laboratory use:
• IEC 61010-1, EN 61010-1
• UL 61010-1, CAN/CSA-C22.2 No. 61010-1
Note Refer to the product label, or visit ni.com/certification, search by model
number or product line, and click the appropriate link in the Certification column for UL
and other safety certifications.
Electromagnetic Compatibility
The NI 781xR is designed to meet the requirements of the following
standards of EMC for electrical equipment for measurement, control,
and laboratory use:
• EN 61326 EMC requirements; Minimum Immunity
• EN 55011 Emissions; Group 1, Class A
• CE, C-Tick, ICES, and FCC Part 15 Emissions; Class A
Appendix A Specifications
Note For EMC compliance, operate this device with shielded cabling.
CE Compliance
This product meets the essential requirements of applicable European
Directives, as amended for CE marking, as follows:
• 73/23/EEC; Low-Voltage Directive (safety)
• 89/336/EEC; Electromagnetic Compatibility Directive (EMC)
Note Refer to the Declaration of Conformity (DoC) for this product for any additional
regulatory compliance information. To obtain the DoC for this product, visit
ni.com/certification, search by model number or product line, and click the
appropriate link in the Certification column.
Waste Electrical and Electronic Equipment (WEEE)
EU Customers At the end of their life cycle, all products must be sent to a WEEE recycling
center. For more information about WEEE recycling centers and National Instruments
WEEE initiatives, visit
© National Instruments Corporation A-5 NI 781xR User Manual
ni.com/environment/weee.htm.
Connecting I/O Signals
This appendix describes how to make input and output signal connections
to the NI 781xR I/O connectors.
The NI 781xR has four DIO connectors with 40 DIO lines per connector.
Figure B-1 shows the I/O connector locations for the NI 781xR. The I/O
connectors are numbered starting at zero.
B
© National Instruments Corporation B-1 NI 781xR User Manual
Appendix B Connecting I/O Signals
PCI-781xR
CONNECTOR 0 (DIO)
1
CONNECTOR 1 (DIO)
CONNECTOR 3 (DIO)
CONNECTOR 2 (DIO)
CONNECTOR 0 (DIO)CONNECTOR 1 (DIO)
CONNECTOR 3 (DIO)CONNECTOR 2 (DIO)
2
1 Connector Overlay for the
NI PXI-781x
2 Connector Overlay for the
NI PCI-781x
Figure B-1. NI 781xR Connector Locations
NI 781xR User Manual B-2 ni.com
Appendix B Connecting I/O Signals
Figure B-2 shows the I/O connector pin assignments for the I/O connectors
on the NI 781xR.
DIO39
DIO37
DIO35
DIO33
DIO31
DIO29
DIO27
DIO26
DIO25
DIO24
DIO23
DIO22
DIO21
DIO20
DIO19
DIO18
DIO17
DIO16
DIO15
DIO14
DIO13
DIO12
DIO11
DIO10
DIO9
DIO8
DIO7
DIO6
DIO5
DIO4
DIO3
DIO2
DIO1
DIO0
68 34
67 33
66 32
65 31
64 30
63 29
62 28
61 27
60 26
59 25
58 24
57 23
56 22
55 21
54 20
53 19
52 18
51 17
50 16
49 15
48 14
47 13
46 12
45 11
44 10
43 9
42 8
41 7
40 6
39 5
38 4
37 3
36 2
35 1
DIO38
DIO36
DIO34
DIO32
DIO30
DIO28
+5V
+5V
DGND
DGND
DGND
DGND
DGND
DGND
DGND
DGND
DGND
DGND
DGND
DGND
DGND
DGND
DGND
DGND
DGND
DGND
DGND
DGND
DGND
DGND
DGND
DGND
DGND
DGND
Figure B-2. NI 781xR I/O Connector Pin Assignments
To access the signals on the I/O connectors, you must connect a cable from
the I/O connector to a signal accessory. Plug the small VHDCI connector
© National Instruments Corporation B-3 NI 781xR User Manual
Appendix B Connecting I/O Signals
end of the cable into the appropriate I/O connector and connect the other
end of the cable to the appropriate signal accessory.
Table B-1. I/O Connector Signal Descriptions
Signal Name Reference Direction Description
+5V DGND Output +5 VDC Source—These pins supply 5 V from the computer
DGND — — Digital Ground—These pins supply the reference for the
DIO<0..39> DGND Input or
Output
power supply using a self-resetting 1 A fuse. No more than
250 mA should be pulled from a single pin.
digital signals at the I/O connector as well as the 5 V supply.
Digital I/O signals.
Caution Connections that exceed any of the maximum ratings of input or output signals
on the NI 781xR can damage the NI 781xR and the computer. Maximum input ratings for
each signal are given in the Protection (Volts) On/Off column of Table B-2. NI is not liable
for any damage resulting from such signal connections.
Table B-2. NI 781xR I/O Signal Summary
Signal
Type and
Signal Name
+5V DO — — — — — —
DGND DO — — — — — —
DIO<0..39>
Connector<0..3>
DIO = Digital Input/Output DO = Digital Output
Direction
DIO — –0.5 to +7.0 5.0 at 2.4 5.0 at 0.4 12 ns —
Impedance
Input/
Output
Protection
(Volts)
On/Off
Source
(mA at V)
Sink
(mA at V)
Rise
Time
Connecting to CompactRIO Extension I/O Chassis
You can use the CompactRIO R Series Expansion chassis and CompactRIO
I/O modules with the NI 781xR. Refer to the CompactRIO R Series
Expansion System Installation Instructions for information about
connecting the chassis to the NI 781xR.
Bias
NI 781xR User Manual B-4 ni.com
Connecting to SSR Signal Conditioning
NI provides cables that allow you to connect signals from the NI 781xR
directly to SSR backplanes for digital signal conditioning.
The NSC68-5050 cable is designed to connect the signals on the NI 781xR
DIO connectors directly to SSR backplanes for digital signal conditioning.
This cable has a 68-pin male VHDCI connector on one end that plugs into
the NI 781xR DIO connectors. The other end of this cable provides two
50-pin female headers.
Each of these 50-pin headers can be plugged directly into an eight-, 16-,
24-, or 32-channel SSR backplane for digital signal conditioning. One of
the 50-pin headers contains DIO lines <0..23> from the NI 781xR DIO
connector. These lines are mapped to slots <0..23> on an SSR backplane in
sequential order. The other 50-pin header contains DIO lines <24..39> from
the NI 781xR DIO connector. These lines are mapped to slots <0..15> on
an SSR backplane in sequential order. You can connect to an SSR
backplane containing a number channels that does not equal the number of
lines on the NSC68-5050 cable header. In this case, you have access only
to the channels that exist on both the SSR backplane and the NSC68-5050
cable header you are using.
Appendix B Connecting I/O Signals
Figure B-3 shows the connector pinouts when using the NSC68-5050
cable.
© National Instruments Corporation B-5 NI 781xR User Manual
Appendix B Connecting I/O Signals
11
13
15
17
19
21
23
25
27
29
31
33
35
37
39
41
43
45
47
49
2
1
4
3
6
5
8
7
10
9
12
14
16
18
20
22
24
26
28
30
32
34
36
38
40
42
44
46
48
50
DIO23
DIO22
DIO21
DIO20
DIO19
DIO18
DIO17
DIO16
DIO15
DIO14
DIO13
DIO12
DIO11
DIO10
DIO9
DIO8
DIO7
DIO6
DIO5
DIO4
DIO3
DIO2
DIO1
DIO0
+5V
DIO 0–23 Connector
Pin Assignment
NC
NC
NC
NC
NC
NC
NC
NC
NC
DGND
DGND
DGND
DGND
DGND
DGND
DGND
DGND
DGND
DGND
DGND
DGND
DGND
DGND
DGND
DGND
NC
NC
NC
NC
NC
NC
NC
NC
DIO39
DIO38
DIO37
DIO36
DIO35
DIO34
DIO33
DIO32
DIO31
DIO30
DIO29
DIO28
DIO27
DIO26
DIO25
DIO24
+5V
DIO 24–39 Connector
Pin Assignment
11
13
15
17
19
21
23
25
27
29
31
33
35
37
39
41
43
45
47
49
2
1
4
3
6
5
8
7
10
9
12
14
16
18
20
22
24
26
28
30
32
34
36
38
40
42
44
46
48
50
NC
NC
NC
NC
NC
NC
NC
NC
NC
NC
NC
NC
NC
NC
NC
DGND
DGND
DGND
DGND
DGND
DGND
DGND
DGND
DGND
DGND
Figure B-3. Connector Pinouts for Use with the NSC68-5050 Cable
NI 781xR User Manual B-6 ni.com
Using the SCB-68
Shielded Connector Block
This appendix describes how to connect input and output signals to the
NI 781xR with the SCB-68 shielded connector block.
The SCB-68 has 68 screw terminals for I/O signal connections. To use the
SCB-68 with the NI 781xR, you must configure the SCB-68 as a
general-purpose connector block. Figure C-1 illustrates the
general-purpose switch configuration.
S5 S4 S3
C
S1
S2
Figure C-1. General-Purpose Switch Configuration for the SCB-68 Terminal Block
After configuring the SCB-68 switches, you can connect the I/O signals to
the SCB-68 screw terminals. Refer to Appendix B, Connecting I/O Signals,
for the connector pin assignments for the NI 781xR. After connecting
I/O signals to the SCB-68 screw terminals, you can connect the SCB-68 to
the NI 781xR with the SH68-C68-S shielded cable.
© National Instruments Corporation C-1 NI 781xR User Manual
Technical Support and
Professional Services
Visit the following sections of the National Instruments Web site at
ni.com for technical support and professional services:
• Support—Online technical support resources at
include the following:
– Self-Help Resources—For answers and solutions, visit the
award-winning National Instruments Web site for software drivers
and updates, a searchable KnowledgeBase, product manuals,
step-by-step troubleshooting wizards, thousands of example
programs, tutorials, application notes, instrument drivers, and
so on.
– Free Technical Support—All registered users receive free Basic
Service, which includes access to hundreds of Application
Engineers worldwide in the NI Developer Exchange at
ni.com/exchange. National Instruments Application Engineers
make sure every question receives an answer.
For information about other technical support options in your
area, visit
ni.com/contact.
• Training and Certification—Visit
self-paced training, eLearning virtual classrooms, interactive CDs,
and Certification program information. You also can register for
instructor-led, hands-on courses at locations around the world.
• System Integration—If you have time constraints, limited in-house
technical resources, or other project challenges, National Instruments
Alliance Partner members can help. To learn more, call your local
NI office or visit
• Declaration of Conformity (DoC)—A DoC is our claim of
compliance with the Council of the European Communities using
the manufacturer’s declaration of conformity. This system affords
the user protection for electronic compatibility (EMC) and product
safety. You can obtain the DoC for your product by visiting
ni.com/certification.
ni.com/services or contact your local office at
ni.com/alliance.
D
ni.com/support
ni.com/training for
© National Instruments Corporation D-1 NI 781xR User Manual
Appendix D Technical Support and Professional Services
• Calibration Certificate—If your product supports calibration,
you can obtain the calibration certificate for your product at
ni.com/calibration.
If you searched
ni.com and could not find the answers you need, contact
your local office or NI corporate headquarters. Phone numbers for our
worldwide offices are listed at the front of this manual. You also can visit
the Worldwide Offices section of
ni.com/niglobal to access the branch
office Web sites, which provide up-to-date contact information, support
phone numbers, email addresses, and current events.
NI 781xR User Manual D-2 ni.com
Glossary
Symbol Prefix Value
ppico10
µ micro 10
m milli 10
Mmega10
A
A Amperes.
ASIC Application-Specific Integrated Circuit—A proprietary semiconductor
component designed and manufactured to perform a set of specific
functions.
B
–12
–6
–3
6
bipolar A signal range that includes both positive and negative values (for example,
–5 to +5 V).
C
CCelsius.
CalDAC Calibration DAC.
CH Channel—Pin or wire lead to which you apply or from which you read the
analog or digital signal. Analog signals can be single-ended or differential.
For digital signals, you group channels to form ports. Ports usually consist
of either four or eight digital channels.
cm Centimeter.
CMOS Complementary metal-oxide semiconductor.
© National Instruments Corporation G-1 NI 781x R User Manual
Glossary
CMRR Common-mode rejection ratio—A measure of an instrument’s ability to
reject interference from a common-mode signal, usually expressed in
decibels (dB).
common-mode
voltage
CompactPCI Refers to the core specification defined by the PCI Industrial Computer
Any voltage present at the instrumentation amplifier inputs with respect to
amplifier ground.
Manufacturer’s Group (PICMG).
D
D/A Digital-to-analog.
DAC Digital-to-analog converter—An electronic device, often an integrated
circuit, that converts a digital number into a corresponding analog voltage
or current.
DAQ Data acquisition—A system that uses the computer to collect, receive, and
generate electrical signals.
dB Decibel—The unit for expressing a logarithmic measure of the ratio of
two signal levels: dB = 20log10 V1/V2, for signals in volts.
DC Direct current.
DGND Digital ground signal.
DIFF Differential mode.
DIO Digital input/output.
DIO<i> Digital input/output channel signal.
DMA Direct memory access—A method by which data can be transferred
to/from computer memory from/to a device or memory on the bus while the
processor does something else. DMA is the fastest method of transferring
data to/from computer memory.
DNL Differential nonlinearity—A measure in LSB of the worst-case deviation of
code widths from their ideal value of 1 LSB.
DO Digital output.
NI 781xR User Manual G-2 © National Instruments Corporation
Glossary
E
EEPROM Electrically erasable programmable read-only memory—ROM that can be
erased with an electrical signal and reprogrammed.
F
FPGA Field-Programmable Gate Array.
FPGA VI A configuration that is downloaded to the FPGA and that determines the
functionality of the hardware.
G
glitch An unwanted signal excursion of short duration that is usually unavoidable.
H
hHour.
HIL Hardware-in-the-loop.
Hz Hertz.
I
I/O Input/output—The transfer of data to/from a computer system involving
communications channels, operator interface devices, and/or data
acquisition and control interfaces.
INL Relative accuracy.
L
LabVIEW Laboratory Virtual Instrument Engineering Workbench. LabVIEW is a
graphical programming language that uses icons instead of lines of text to
create programs.
LSB Least significant bit.
© National Instruments Corporation G-3 NI 781x R User Manual
Glossary
M
m Meter.
max Maximum.
MIMO Multiple input, multiple output.
min Minimum.
MIO Multifunction I/O.
monotonicity A characteristic of a DAC in which the analog output always increases as
the values of the digital code input to it increase.
mux Multiplexer—A switching device with multiple inputs that sequentially
connects each of its inputs to its output, typically at high speeds, in order to
measure several signals with a single analog input channel.
N
noise An undesirable electrical signal—Noise comes from external sources such
as the AC power line, motors, generators, transformers, fluorescent lights,
CRT displays, computers, electrical storms, welders, radio transmitters,
and internal sources such as semiconductors, resistors, and capacitors.
Noise corrupts signals you are trying to send or receive.
NRSE Nonreferenced single-ended mode—All measurements are made with
respect to a common (NRSE) measurement system reference, but the
voltage at this reference can vary with respect to the measurement system
ground.
O
OUT Output pin—A counter output pin where the counter can generate various
TTL pulse waveforms.
NI 781xR User Manual G-4 © National Instruments Corporation
Glossary
P
PCI Peripheral Component Interconnect—A high-performance expansion bus
architecture originally developed by Intel to replace ISA and EISA. It is
achieving widespread acceptance as a standard for PCs and workstations.
PCI offers a theoretical maximum transfer rate of 132 MB/s.
port (1) A communications connection on a computer or a remote controller.
(2) A digital port, consisting of four or eight lines of digital input and/or
output.
ppm Parts per million.
pu Pull-up.
PWM Pulse-width modulation.
PXI PCI eXtensions for Instrumentation—An open specification that builds off
the CompactPCI specification by adding instrumentation-specific features.
R
RAM Random-access memory—The generic term for the read/write memory that
is used in computers. RAM allows bits and bytes to be written to it as well
as read from. Various types of RAM are DRAM, EDO RAM, SRAM, and
VRAM.
resolution The smallest signal increment that can be detected by a measurement
system. Resolution can be expressed in bits, in proportions, or in percent
of full scale. For example, a system has 12-bit resolution, one part in
4,096 resolution, and 0.0244% of full scale.
RIO Reconfigurable I/O.
rms Root mean square.
RSE Referenced single-ended mode—All measurements are made with respect
to a common reference measurement system or a ground. Also called a
grounded measurement system.
© National Instruments Corporation G-5 NI 781x R User Manual
Glossary
S
s Seconds.
S Samples.
S/s Samples per second—Used to express the rate at which a DAQ board
samples an analog signal.
signal conditioning The manipulation of signals to prepare them for digitizing.
slew rate The voltage rate of change as a function of time. The maximum slew rate
of an amplifier is often a key specification to its performance. Slew rate
limitations are first seen as distortion at higher signal frequencies.
T
THD Total harmonic distortion—The ratio of the total rms signal due to
harmonic distortion to the overall rms signal, in decibel or a percentage.
thermocouple A temperature sensor created by joining two dissimilar metals. The
junction produces a small voltage as a function of the temperature.
TTL Transistor-transistor logic.
two’s complement Given a number x expressed in base 2 with n digits to the left of the radix
point, the (base 2) number 2n – x.
V
V Volts.
VDC Volts direct current.
VHDCI Very high density cabled interconnect.
VI Virtual Instrument—Program in LabVIEW that models the appearance and
function of a physical instrument.
V
IH
V
IL
NI 781xR User Manual G-6 © National Instruments Corporation
Volts, input high.
Volts, input low.
Glossary
V
OH
V
OL
V
rms
Volts, output high.
Volts, output low.
Volts, root mean square.
W
waveform Multiple voltage readings taken at a specific sampling rate.
© National Instruments Corporation G-7 NI 781x R User Manual
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