National Instruments SCXI-1121 User Manual

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SCXI

SCXI-1121 User Manual

Four-Channel Isolated Universal Transducer Module for Signal Conditioning

SCXI-1121 User Manual

September 1999 Edition

Part Number 320426C-01

Worldwide Technical Support and Product Information

www.natinst.com

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For further support information, see the Technical Support Resources appendix. To comment on the documentation, send e-mail to techpubs@natinst.com.

Important Information

Warranty

The SCXI-1121 is warranted against defects in materials and workmanship f or a period of one year from the date of shipment, as evidenced by receipts or other documentation. National Instruments will, at its option, repair or replace equipment that proves to be defective during the warranty period. T his w arran ty i ncludes part s and l abo r.

A Return Material Authorization (RMA) number must be obtained from the factory and clearly marked on the outside of the package before any equipment will be accepted for warranty work. National Instruments will pay the shipping costs of returning to the owner parts which are covered by warrant y.

National Instruments believes that the information in this document is accurate. The document has been carefully reviewed for technical accuracy. In the event that technical or typographical errors exist, National Instruments reserves the right to make changes to subsequent editions of this document without prior notice to holders of this edition. The reader should consult National Instruments if errors are suspected. In no even t shall Nati on al Inst rum ents be l iable fo r any dama ges aris in g o ut of or related to this document or the information contained in it.

XCEPT AS SPECIFIED HEREIN

WARRANTY OF MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE OR NEGLIGENCE ON THE PART OF NATIONAL INSTRUMENTS SHALL BE LIMITED TO THE AMOUNT THERETOFORE PAID BY THE CUSTOMER

ATIONAL INSTRUMENTS WILL NOT BE LIABLE FOR DAMAGES RESULTING FROM LOSS OF DATA, PROFITS, USE OF PRODUCTS, OR INCIDENTAL

OR CONSEQUENTIAL DAMAGES, EVEN IF ADVISED OF THE POSSIBILITY THEREOF

will apply regardless of the form of action, whether in contract or tort, including negligence. Any action against National Instruments must be brought within one year after the cause of action accrues. National Instruments shall not be liable for any delay in performance due to causes beyond its reasonable control. The warranty provided herein does not cover damages, defects, malfunctions, or service failures caused by owner’s failure to follow the National Instruments installation, operation, or maintenance instructions; owner’s modification of the product; owner’s abuse, misuse, or negligent acts; and power failure or surges, fire, flood, accident, actions of third part ies, o r other eve nts o ut side reasonab le co ntrol .

ATIONAL INSTRUMENTS MAKES NO WARRANTIES, EXPRESS OR IMPLIED, AND SPECIFICALLY DISCLAIMS ANY

, N

Copyright

Under the copyright laws, this publication may not be reproduced or transmitted in any form, electronic or mechanical, including photocopying, recording, sto rin g in an i nform atio n ret rieval s ystem , o r t ranslati ng , i n w hole o r in part, w it ho ut the prior written consent of National Instruments Corporation.

Trademarks

LabVIEW™, natinst.com™, National Instruments™, NI-DAQ™, RTSI™, and SCXI™ are trademarks of National Instruments Corporation.

Product and company names mentioned herein are trademarks or trade names of their respective companies.

USTOMER’S RIGHT TO RECOVER DAMAGES CAUSED BY FAULT

. C

. This limitation of the liability of National Instruments

WARNING REGARDING USE OF NATIONAL INSTRUMENTS PRODUCTS

(1) NATIONAL INSTRUMENTS PRODUCTS ARE NOT DESIGNED WITH COMPONENTS AND TESTING FOR A LEVEL OF RELIABILITY SUITABLE FOR USE IN OR IN CONNECTION WITH SURGICAL IMPLANT S OR AS CRITICAL COMPONENTS IN ANY LIFE SUPPORT SYSTEMS WHOSE FAILURE TO PERFORM CAN REASONABLY BE EXPECTED TO CAUSE SIGNIFICANT INJURY TO A HUMAN.

(2) IN ANY APPLICATION, INCLUDING THE ABOVE, RELIABILITY OF OPERATION O F THE SOFTWARE PRODUCTS CAN BE IMPAIRED BY ADVERSE FACTORS, INCLUDING BUT NOT LIMITED TO FLUCTUATIONS IN ELECTRICAL POWER SUPPLY, COMPUTER HARDWARE MALFUNCTIONS, COMPUTER OPERATING SYSTEM SOFTWARE FITNESS, FITNESS OF COMPILERS AND DEVELOPMENT SOFTWARE USED TO DEVELOP AN APPLICATION, INSTALLATION ERRORS, SOFTWARE AND HARDWARE COMPATIBILITY PROBLEMS, MALFUNCTIONS OR FAILURES OF ELECTRONIC MONITORING OR CONTROL DEVICES, TRANSIENT FAILURES OF ELECTRONIC SYSTEMS (HARDWARE AND/OR SOFTWARE), UNANTICIPATED USES OR MISUSES, OR ERRORS ON THE PART OF THE USER OR APPLICATIONS DESIGNER (ADVERSE FACTORS SUCH AS THESE ARE HEREAFTER COLLECTIVELY TERMED “SYSTEM FAILURES”). AN Y A PPLICATION WHE RE A SYSTEM FAILURE WOULD CREATE A RISK OF HARM TO PROPERTY OR PERSONS (INCLUDING THE RISK OF BODILY INJURY AND DEATH) SHOULD NOT BE RELIANT SOLELY UPON ONE FORM OF ELECTRONIC SYSTEM DUE TO THE RISK OF SYSTEM FAILURE. TO AVOID DAMAGE, INJURY, OR DEATH , TH E U SER OR APPLICATION DESIGNER MUST TAKE REASONABLY PRUDENT STEPS TO PROTECT AGAINST SYSTEM FAILURES, INCLUDING BUT NOT LIMITED TO BACK-UP OR SHUT DOWN MECHANISMS. BECAUSE EACH END-USER SYSTEM IS CUSTOMIZED AND DIFFERS FROM NATIONAL INSTRUMENTS' TESTING PLATFORMS AND BECAUSE A USER OR APPLICATION DESIGNER MAY USE NATIONAL INSTRUMENTS PRODUCTS IN COMBINATION WITH OTHER PRODUCTS IN A MANNER NOT EVALUATED OR CONTEMPLATED BY NATIONAL INSTRUMENTS, THE USER OR APPLICATION DESIGNER IS ULTIMATELY RESPONSIBL E FOR VERIFYING AND VALIDATING THE SUITABILITY OF NATIONAL INSTRUMENT S PRODUCTS WHENEVE R NATIONAL INSTRUMENTS PRODUCTS ARE INCORPORATED IN A SYSTEM OR A PPLICATION, INCL UDING , WITHOUT LIMITATION, THE APPROPRIATE DESIGN, PROCESS AND SAFETY LEVEL OF SUCH SYSTEM OR APPLICATION.

About This Manual

Conventions ...................................................................................................................xi

Related Documentation........................................... .......................................................xii

Chapter 1 Introduction

What Your Kit Should Contain .....................................................................................1-2

Optional Software.............................................................. ............................................1-2

Optional Equipment.......................................................................................................1-4

Custom Cables.................................................................................................1-5

Unpacking......................................................................................................................1-6

Chapter 2 Configuration and Installation

Module Configuration....................................................................................................2-1

Digital Signal Connections..............................................................................2-3

Jumper W44......................................................................................2-3

Jumper W38......................................................................................2-4

Jumper W32......................................................................................2-4

Using Jumpers W32 and W38 ..........................................................2-4

Analog Configuration......................................................................................2-6

Grounding, Shielding, and Reference Mode Selection.....................2-6

Input Channel Jumpers......................................................................2-8

Excitation Jumpers......................................... ...................................2-9

Hardware Installation.....................................................................................................2-14

Signal Connections .................................................... ....................................................2-15

Front Connector...............................................................................................2-16

Front Connector Signal Descriptions ..............................................................2-18

Analog Input Channels......................................................................2-20

Excitation Channels ........................................................ ..................2-22

Temperature Sensor Connection.......................................................2-22

Connector-and-Shell Assembly ........................................................2-22

SCXI-1320, SCXI-1328, and SCXI-1321 Terminal Blocks.............2-24

Rear Signal Connector.....................................................................................2-37

Rear Signal Connector Signal Descriptions ...................................................2-38

Analog Output Signal Connections................................................... 2-39

Digital I/O Signal Connections.........................................................2-40

Timing Requirements and Communication Protocol........................2-42

Communication Signals....................................................................2-42

Contents

Chapter 3 Theory of Operation

Functional Overview.....................................................................................................3-1

SCXIbus Connector ........................................................................................3-3

SCXIbus Connector Signal Descriptions........................................................3-4

Digital Interface............................................................. ................................................3-6

Digital Control Circuitry ...............................................................................................3-7

Analog and Timing Circuitry ........................................................................................3-8

Analog Input Channels....................................................................................3-8

Excitation Output Channels............................................................................3-11

Calibration.......................................................................................................3-11

Analog Output Circuitry .................................................................................3-15

Scanning Modes .............................................................. ..............................................3-17

Single-Module Parallel Scanning....................................................................3-17

Multiplexed Scanning.....................................................................................3-17

Calibration Equipment Requirements ..............................................3-11

Offset Null Adjust ............................................................................3-12

Excitation Adjust..............................................................................3-13

Single-Module Multiplexed Scanning..............................................3-18

Multiple-Module Multiplexed Scanning ..........................................3-19

Multiple-Chassis Scanning...............................................................3-20

Chapter 4 Register Descriptions

Register Description......................................................................................................4-1

SCXI-1121 Registers ......................................................................................4-1

Slot 0 Register Descriptions............................................................................4-5

Chapter 5 Programming

Programming Considerations........................................................................................5-1

Notation...........................................................................................................5-1

Initialization......................................................................................5-3

Single-Channel Measurements .......................................................................5-4

Direct Measurements........................................................................5-4

Indirect Measurements .....................................................................5-5

Scanning Measurements ...................................... ...........................................5-7

1. Data Acquisition Board Setup Programming............................... 5-7

SCXI-1121 User Manual vi www.natinst.com

2. Module Programming ...................................................................5-10

3. Programming the Slot 0 Hardscan Circuitry.................................5-13

4. Acquisition Enable, Triggering, and Servicing.............................5-14

Scanning Examples................................... ... ..................................................................5-15

Example 1........................................................................................................5-15

Example 2........................................................................................................5-15

Example 3........................................................................................................5-16

Appendix A Specifications

Appendix B Rear Signal Connector

Appendix C SCXIbus Connector

Appendix D SCXI-1121 Front Connector

Contents

Appendix E SCXI-1121 Cabling

Appendix F Revision A and B Photo and Parts Locator Diagrams

Appendix G Technical Support Resources

Glossary

Index

Contents

Figures

Figure 2-1. SCXI-1121 General Parts Locator Diagram.........................................2-2

Figure 2-2. SCXI-1121 Detailed Parts Locator Diagram........................................2-3

Figure 2-3. SCXI-1121 Front Connector Pin Assignment ......................................2-18

Figure 2-4. Ground-Referenced Signal Connection with

High Common-Mode Voltage ..............................................................2-21

Figure 2-5. Floating Signal Connection Referenced to Chassis Ground for

Better Signal-to-Noise Ratio.................................................................2-21

Figure 2-6. Floating AC-Coupled Signal Connection.............................................2-22

Figure 2-7. AC-Coupled Signal Connection with High Common-Mode Voltage.. 2-22 Figure 2-8. Assembling and Mounting the SCXI-1330

Connector-and-Shell Assembly ............................................................2-25

Figure 2-9. Nulling Circuit ......................................................................................2-29

Figure 2-10. Shunt Circuit.........................................................................................2-30

Figure 2-11. SCXI-1320 Parts Locator Diagram.......................................................2-36

Figure 2-12. SCXI-1328 Parts Locator Diagram.......................................................2-37

Figure 2-13. SCXI-1321 Parts Locator Diagram.......................................................2-38

Figure 2-14. SCXI-1121 Rear Signal Connector Pin Assignment ............................ 2-39

Figure 2-15. SCANCLK Timing Requirements........................................................2-43

Figure 2-16. Slot-Select Timing Diagram.................................................................2-44

Figure 2-17. Serial Data Timing Diagram.................................................................2-45

Figure 2-18. Configuration Register Write Timing Diagram....................................2-46

Figure 2-19. SCXI-1121 Module ID Register Timing Diagram ...............................2-47

Figure 3-1. SCXI-1121 Block Diagram...................................................................3-1

Figure 3-2. SCXIbus Connector Pin Assignment....................................................3-3

Figure 3-3. Digital Interface Circuitry Block Diagram ........................................... 3-6

Figure 3-4. SCXI-1121 Digital Control...................................................................3-7

Figure 3-5. Analog Input Block Diagram................................................................3-9

Figure 3-6. Analog Output Circuitry.......................................................................3-15

Figure 3-7. Single-Module Parallel Scanning .........................................................3-17

Figure 3-8. Single-Module Multiplexed Scanning (Direct) ....................................3-18

Figure 3-9. Single-Module Multiplexed Scanning (Indirect)..................................3-19

Figure 3-10. Multiple-Module Multiplexed Scanning...............................................3-19

Figure 3-11. Multiple-Chassis Scanning ...................................................................3-20

Figure B-1. SCXI-1121 Rear Signal Connector Pin Assignment ............................ B-1

Figure C-1. SCXIbus Connector Pin Assignment....................................................C-2

Figure D-1. SCXI-1121 Front Connector Pin Assignment......................................D-2

Figure E-1. SCXI-1340 Installation .........................................................................E-4

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Tables

Contents

Figure E-2. SCXI-1180 Rear Connections...............................................................E-9

Figure E-3. SCXI-1180 Front Panel Installation......................................................E-10

Figure E-4. Cover Removal......................................................................................E-11

Figure F-1. Revision A and B SCXI-1121 Signal Conditioning Module................F-1

Figure F-2. Revision A and B SCXI-1121 General Parts Locator Diagram............F-2

Figure F-3. Revision A and B SCXI-1121 Detailed Parts Locator Diagram...........F-3

Table 2-1. Digital Signal Connections, Jumper Settings........................................2-6

Table 2-2. Jumper W33 Settings.............................................................................2-8

Table 2-3. Gain Jumper Allocation.........................................................................2-9

Table 2-4. Gain Jumper Positions...........................................................................2-9

Table 2-5. Filter Jumper Allocation........................................................................2-10

Table 2-6. Voltage and Current Mode Excitation Jumper Setup............................2-11

Table 2-7. Maximum Load per Excitation Channel...............................................2-12

Table 2-8. Excitation Level Jumper Selection........................................................2-12

Table 2-9. Completion Network Jumpers............................................................... 2-14

Table 2-10. Trimmer Potentiometer and Corresponding Channel ...........................2-27

Table 2-11. Nulling Resistors and Corresponding Channel.....................................2-27

Table 2-12. Jumper Settings of the Nulling Circuits................................................2-29

Table 2-13. Jumper Settings on the SCXI-1320 Terminal Block.............................2-33

Table 2-14. Jumper Settings on the SCXI-1328 Terminal Block.............................2-34

Table 2-15. Jumper Settings on the SCXI-1321 Terminal Block.............................2-34

Table 2-16. SCXIbus to SCXI-1121 Rear Signal Connector to

Data Acquisition Board Pin Equivalences ............................................2-42

Table 3-1. SCXIbus Equivalents for the Rear Signal Connector ...........................3-5

Table 3-2. Calibration Potentiometer Reference Designators................................3-14

Table 5-1. SCXI-1121 Rear Signal Connector Pin Equivalences ..........................5-2

Table E-1. SCXI-1121 and MIO-16 Pinout Equivalences......................................E-2

Table E-2. SCXI-1341 and SCXI-1344 Pin Translations.......................................E-5

Table E-3. SCXI-1342 Pin Translations .................................................................E-7

Table E-4. SCXI-1343 Pin Connections.................................................................E-14

About This Manual

This manual describes the electrical and mechanical aspects of the SCXI-1121 and contains information concerning its operation and programming. The SCXI-1121 is a member of the National Instruments Signal Conditioning eXtensions for Instrumentation (SCXI) Series for the National Instruments data acquisition plug-in boards. This board is designed for signal conditioning of strain gauges, RTDs, thermistors, thermocouples, volt and millivolt sources, and 4 to 20 mA sources or 0 to 20 mA process-current sources where high common-mode voltages exist. The SCXI-1121 operates as four isolated input channels and four isolated excitation channels. Each channel is isolated and independently configurable via jumpers.

This manual describes the installation, basic programming considerations, and theory of operation for the SCXI-1121.

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, DBIO<3..0>.

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. This icon denotes a warning, which advises you of precautions to take to

avoid being electrically shocked.

bold Bold text denotes items that you must select or click on in the software,

such as menu items and dialog box options. Bold text also denotes parameter names.

italic Italic text denotes variables, emphasis, a cross reference, or an introduction

to a key concept. This font also denotes text that is a placeholder for a word or value that you must supply.

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, and code excerpts.

monospace italic

Italic text in this font denotes text that is a placeholder for a word or value that you must supply.

What Your Kit Should Contain

The contents of the SCXI-1121 kit (part number 776572-21) are listed as follows:

Kit Component Part Number

SCXI-1121 module 181700-01 SCXI-1121 User Manual 320426-01

If your kit is missing any of the components, contact Nati onal Instruments .

Optional Software

This manual contains complete instructions for directly programming the SCXI-1121. You can order separate software packages for controlling the SCXI-1121 from National Instruments.

When you combine the PC, AT, and MC data acquisition boards with the SCXI-1121, you can use LabVIEW for Windows or LabW indows for DOS. LabVIEW and LabWindows are inno vativ e program development software packages for data acquisition and control applications. LabVIEW uses graphical programming, whereas LabWindows enhances Microsoft C and QuickBASIC. Both packages include extensive libraries for data acquisition, instrument control, data analysis, and graphical data presentation.

Your National Instruments data acquisition board is shipped with the NI-DA Q software. NI-DA Q has a library of functions that you can call from your application programming environment. These functions include routines for analog input (A/D conversion), buffered data acquisition (high-speed A/D conversion), analog output (D/A conversion), waveform generation, digital I/O, counter/timer, SCXI, RTSI, and self-calibration. NI-DAQ maintains a consistent software interface among its different versions so you can switch between platforms with minimal modifications to your code.

You can also use the SCXI-1121, together with the PC, AT, and MC data acquisition boards, with NI-DAQ software for DOS/Windows/ LabWindows/CVI. NI-DAQ software for DOS/Windows/ LabWindows/CVI comes with language interfaces for Professional BASIC, T urbo Pascal, T urbo C, T urbo C++, Borland C++, and Microsoft C

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Chapter 1 Introduction

for DOS and Visual Basic, Turbo Pascal, Microsoft C with SDK, and Borland C++ for Windows. NI-DAQ software for DOS/Windows/LabWindows is on high-density 5.25 in. and 3.5 in. diskettes.

You can use the SCXI-1121, together with the Lab-LC or NB Series data acquisition boards, with LabVIEW for Macintosh, a software system that features interactive graphics, a state-of-the-art user interface, and a powerful graphical programming language. The LabVIEW Data Acquisition VI Library, a series of VIs for using LabVIEW with National Instruments boards, is included with LabVIEW. The LabVIEW Data Acquisition VI Library is functionally equivalent to the NI-DAQ software for Macintosh.

You can also use the SCXI-1121, combined with the NB Series data acquisition boards, with NI-DAQ software for Macintosh. NI-DAQ software for Macintosh, which is shipped with all National Instruments Macintosh data acquisition boards, comes with language interfaces for MPW C, THINK C, Pascal, and Microsoft QuickBASIC. Any language that uses Device Manager Toolbox calls can access NI-DAQ software for Macintosh.

Chapter 1 Introduction

Optional Equipment

NB6 cable

0.5 m 181305-01

1.0 m 181305-10 SCXI-1320 front terminal block 776573-20 SCXI-1321 offset-null and shunt-calibration terminal block 776573-21 SCXI-1328 high-accuracy isothermal terminal block 776573-28 SCXI-1330 32-pin connector-and-shell assembly 776573-30 SCXI-1340 cable assembly 776574-40 SCXI-1341 Lab-NB/Lab-PC/Lab-PC+ cable assembly 776574-41 SCXI-1342 PC-LPM-16 cable assembly 776574-42 SCXI-1343 rear screw terminal adapter 776574-43 SCXI-1344 Lab-LC cable assembly 776574-44 SCXI-1346 shielded multichassis cable adapter 776574-46

Equipment Part Number

SCXI-1347 SCXI shielded cable assembly

with 1 m cable 776574-471 with 2 m cable 776574-472 with 5 m cable 776574-475 with 10 m cable 776574-470

SCXI-1349 SCXI shielded cable assembly

with 1 m cable 776574-491 with 2 m cable 776574-492 with 5 m cable 776574-495

with 10 m cable 776574-490 SCXI-1350 multichassis adapter 776575-50 SCXI process-current resistor kit 776582-01 Standard ribbon cable

0.5 m 180524-05

1.0 m 180524-10

SCXI-1121 User Manual 1-4 www.natinst.com

Custom Cables

Chapter 1 Introduction

Refer to the Signal Connections section in Chapter 2, Configuration and

Installation, and to Appendix E, SCXI-1121 Cabling, for additional

information on cabling, connectors, and adapters.

The SCXI-1121 rear signal connector is a 50-pin male ribbon-cable header. The manufacturer part number used by National Instruments for this header is as follows:

• AMP Inc. (part number 1-103310-0) The mating connector for the SCXI-1121 rear signal connector is a

50-position polarized ribbon-socket connector with strain relief. National Instruments uses a polarized or keyed connector to prevent inadvertent upside-down connection to the SCXI-1121. Recommended manufacturer part numbers for this mating connector are as follows:

• Electronic Products Division/3M (part number 3425-7650)

• T&B/Ansley Corporation (part number 609-5041CE) Standard 50-conductor, 28 AWG, stranded ribbon cables that can be used

with these connectors are as follows:

• Electronic Products Division/3M (part number 3365/50)

• T&B/Ansle y Corporation (part number 171-50) The SCXI-1121 front connector is a 32-pin DIN C male connector with

column A and column C even pins only. The manufacturer part number used by National Instruments for this connector is as follows:

• Panduit Corporation (part number 100-932-023) The mating connector for the SCXI-1121 front connector is a 32-pin DIN C

female connector. National Instruments uses a polarized connector to prevent inadvertent upside-down connection to the SCXI-1121. Recommended manufacturer part numbers for this mating connector are as follows:

• Panduit Corporation (part number 100-932-434 straight-solder eyelet pins)

• Panduit Corporation (part number 100-932-633; right-angle pins)

National Instruments selected these connectors to meet UL 1950 and UL 1244 for 1,500 V

isolation.

rms

Chapter 1 Introduction

Unpacking

Your SCXI-1121 module is shipped in an antistatic package to prevent electrostatic damage to the module. Several components on the module can be damaged by electrostatic discharge. To avoid such damage in handling the module, take the following precautions.

• Touch the antistatic package to a metal part of your SCXI chassis before removing the module from the package.

• Remo ve the module from the package and inspect the module for loose components or any other sign of damage. Notify National Instruments if the module appears damaged in any way. Do not install a damaged module into your SCXI chassis.

SCXI-1121 User Manual 1-6 www.natinst.com

Configuration and Installation

This chapter describes the SCXI-1121 jumper configurations, installation of the SCXI-1121 into the SCXI chassis, signal connections to the SCXI-1121, and cable wiring.

Module Configuration

The SCXI-1121 contains 49 jumpers that are shown in the parts locator diagrams in Figures 2-1 and 2-2.

Figure 2-1.

SCXI-1121 General Parts Locator Diagram

Chapter 2 Configuration and Installation

Figure 2-2. SCXI-1121 Detailed Parts Locator Diagram

The jumpers are used as follows:

• Fixed jumpers – On Revision A and B modules, jumper W32 is unused and should

not be connected. – Jumper W45 is reserved and should not be reconfigured. – On Revision A and B modules, jumper W44 carries the

SLOT0SEL* signal from the rear signal connector, after

buffering, to the SCXIbus INTR* line and should be left in the

factory-set position (position 1). On Revision C or later modules,

jumper W44 does not exist.

• User-configurable jumpers – Jumper W38 carries the SCXIbus MISO line, after buffering, to

the SERDATOUT signal on the rear signal connector.

– On Revision C or later modules, jumper W32 connects a pullup

resistor to the SERDATOUT signal on the rear signal connector.

– Jumper W33 configures the guard, the analog output ground, and

enables the Pseudodifferential Reference mode.

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Chapter 2 Configuration and Installation

– Jumpers W3, W19, W29, and W41 configure the first-stage gain

of input channels 0 through 3, respectively.

– Jumpers W4, W20, W30, and W42 configure the second-stage

gain of input channels 0 through 3, resp ectively.

– Jumpers W5, W21, W31, and W43 configure the first-stage

filtering of input channels 0 through 3, respectively.

– Jumpers W6 and W7, W8 and W9, W10 and W11, and W12 and

W13 configure the second-stage filtering of input channels 0 through 3, respectively.

– Jumpers W14 and W15, W22 and W23, W34 and W35, and W46

and W47 configure the voltage or current mode of operation for excitation channels 0 through 3, respectively.

– Jumpers W16 and W26, W24 and W25, W36 and W37, and W48

and W49 configure the level of excitation for excitation channels 0 through 3, respectively.

– Jumpers W1 and W2, W17 and W18, W27 and W28, and W39

and W40 configure the half-bridge completion network for channels 0 through 3, respectively.

Further configuration of the board is software controlled and will be discussed later in this chapter.

Digital Signal Connections

The SCXI-1121 has three jumpers dedicated for communication between the data acquisition board and the SCXIbus. These jumpers are W32, W38, and W44.

Jumper W44

Position 1 on Revision A and B modules connects, after buffering, SLOT0SEL* to the SCXIbus INTR* line. This is the factory-default setting and should not be changed. In this setting, the data acquisition board controls the SCXIbus INTR* line. See the Timing Requirements and

Communication Protocol section later in this chapter, and Chapter 5, Programming, for information on the use of the INTR* line. See

Appendix E, SCXI-1121 Cabling, for the pin equivalences of the SCXI-1121 rear signal connector and the data acquisition board I/O connector.

Position 3 is reserved and should not be used. This position is not explicitly marked on the module.

Chapter 2 Configuration and Installation

On Revision C or later modules, jumper W44 does not exist. SLOT0SEL* is always buffered to the INTR* line.

Jumper W38

Position 1 connects, after buffering, the SCXIbus MISO line to the SERDATOUT pin of the rear signal connector. In this setting, along with the proper setting of W32, the data acquisition board can read the Module ID Register of the SCXI-1121. See the Timing Requirements and

Communication Protocol section later in this chapter, and Chapter 4, Register Descriptions, for information on reading the Module ID Register.

See Appendix E, SCXI-1121 Cabling, for the pin equivalences of the SCXI-1121 rear signal connector and the data acquisition board I/O connector. This is the factory-default setting.

Position 3 disconnects SERDATOUT from the SCXIbus MISO line.

Jumper W32

On Revision A and B modules, jumper W32 should not be connected. On Revision C or later modules, Position 1 connects a 2.2 kΩ pullup resistor to the SERDATOUT line (factory-default setting), and Position 3 does not connect the pullup resistor to the SERDATOUT line.

Using Jumpers W32 and W38

Set jumpers W32 and W38 as follows: If the SCXI-1121 is not cabled to a data acquisition board, the positions of

these jumpers do not matter, so leav e them in their factory default positions (both in position 1).

If the SCXI-1121 is cabled to a data acquisition board, and the SCXI chassis that the SCXI-1121 is in, is the only SCXI chassis cabled to that data acquisition board, leave the jumpers in their factory default positions (both in position 1).

If the SCXI-1121 is cabled to a data acquisition board, and there are multiple SCXI chassis cabled to that data acquisition board with shielded cables (you are using SCXI-1346 shielded cable multi-chassis adapters), leave the jumpers in their factory default positions (both in position 1).

If the SCXI-1121 is cabled to a data acquisition board, and there are multiple SCXI chassis cabled to that data acquisition board with ribbon cables (you are using SCXI-1350 multi-chassis adapters), leave jumper

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Chapter 2 Configuration and Installation

W38 in its factory default position (position 1). On all but one of the SCXI-1121s that are cabled to the data acquisition board, move jumper W32 to position 3. It does not matter which of the SCXI-1121 modules that are cabled to the data acquisition board has jumper W32 set to position 1. If you have different types of modules cabled to the data acquisition board, those different modules will have jumpers similar to W38 and W32 of the SCXI-1121. Set those jumpers on the different modules using the same method described here for the SCXI-1121.

On Revision A and B SCXI-1121s, jumper W32 is not used. Y ou set jumper W38 as explained in the cases above, except in the case of a multiple chassis ribbon cable system. In a multichassis ribbon cable system with Revision A and B SCXI-1121s cabled to the data acquisition board, you can access the MISO line in only one chassis. Pick one of the chassis and set jumper W38 to position 1 on the SCXI-1121 in that chassis that is cabled to the data acquisition board. On the SCXI-1121s that are in the other chassis and cabled to the data acquisition board, set jumper W38 to position 3. Notice that you will only be able to access digital information from the chassis that has the SCXI-1121 with jumper W38 set to position 1.

Table 2-1. Digital Signal Connections, Jumper Settings

Jumper Description Configuration

W38 Factory setting;

connects MISO to SERDATOUT

•

W38 Parking position

•

W45 Factory setting

•

Chapter 2 Configuration and Installation

Analog Configuration

The SCXI-1121 has 45 analog configuration jumpers.

Table 2-1.

Jumper Description Configuration

W44 Factory setting

W32 Fatory-default setting;

W32 Parking position (not

Digital Signal Connections, Jumper Settings (Continued)

(Revision A and B modules only)

connects pullup to SERDATOUT (Revision C and later)

connected on Revision A or B modules)

•

Before starting, notice that the jumper configurations for each input channel and each excitation channel are similar only the jumper numbers differ . Therefore, when you learn ho w to set up one channel pair (input and excitation), you can set up the other channel pairs as well.

Grounding, Shielding, and Reference Mode Selection

Jumper W33

Position AB-R0 connects the analog reference to the analog output ground (pins 1 and 2 on the rear signal connector). Select this configuration if you are using an RSE data acquisition board. It is not recommended to use a differential input data acquisition board when jumper W33 is in the AB-R0 position.

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Chapter 2 Configuration and Installation

•••••

•

R2 R 1 R 0

•••••

•

R2 R 1 R 0

•••••

•

R2 R 1 R 0

•••••

•

R2 R 1 R 0

Position AB-R1 connects the analog reference to the SCXIbus guard. Position A-R0R1 is the parking position and the factory setting. Position AB-R2 enables the Pseudodifferential Reference mode and

connects the analog reference to the OUTREF pin on the rear signal connector. Select this mode when the SCXI-1121 has to operate with data acquisition boards that have a nonreferenced single-ended (NRSE) input. It is not recommended to use differential-input data acquisition boards when jumper W33 is in the AB-R2 position.

Table 2-2. Jumper W33 Settings

Jumper Description Configuration

W33 Factory setting in

parking position

W33 Connects the

analog reference to AOGND (pins 1 and 2 of the rear signal connector)

W33 Connects SCXIbus

guard to the analog reference

W33 Enables the

Pseudodifferential Reference mode (pin 19 of the rear signal connector is connected to the analog reference)

Chapter 2 Configuration and Installation

Input Channel Jumpers

Gain Jumpers

Each input channel has two gain stages. The first gain stage provides gains of 1, 10, 50, and 100 and the second stage provides gains of 1, 2, 5, 10, and

20. Tables 2-3 and 2-4 show how to set up the gain for each channel.

Table 2-3.

Input Channel

Number

Gain Jumper Allocation

First Gain

Jumper

Second Gain

Jumper

0 W3 W4 1 W19 W20 2 W29 W30 3 W41 W42

The board is shipped to you with the first-stage gain set to 100 (position A) and a second-stage gain set to 10 (position D). To change the gain of your module, move the appropriate jumper on your module to the position indicated in T able 2-4. Refer to Figure 2-2 for the jumper locations on your module.

T o determine the o verall g ain of a giv en channel use the follo wing formula:

Overall gain = First-stage gain × second-stage gain

Table 2-4.

Gain Jumper Positions

Gain Setting Jumper Position

First-stage 1

10 50

100

A (factory setting)

Second-stage 1

2 5

D (factory setting)

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D C B

A B C

Chapter 2 Configuration and Installation

Filter Jumpers

Two-stage filtering is also available on your SCXI-1121 module. The first stage is located in the isolated section of the input channel, whereas the second stage is located in the nonisolated section of the input channel. This permits a higher signal-to-noise ratio by eliminating the noise generated by the isolation amplifier. Furthermore, two filter bandwidths are available—10 kHz and 4 Hz.

Table 2-5.

First Filter Jumper Second Filter Jumper

Input Channel

Number

0 W5-A W5-B W6 W7 1 W21-A W21-B W8 W9 2 W31-A W31-B W10 W11 3 W43-A W43-B W12 W13

4 Hz

(Factory Setting)

Your SCXI-1121 is shipped in the 4 Hz configuration. Always make sure to set both stages to the same bandwidth. This will ensure that the required bandwidth is achieved.

Filter Jumper Allocation

10 kHz

4 Hz

(Factory Setting)

Excitation Jumpers

Current and Voltage Excitation Jumpers

You can configure each excitation channel of your SCXI-1121 to either a Voltage or Current excitation mode. Each channel has two jumpers for this purpose. Set both jumpers in the same mode for correct operation of the excitation channel. Refer to Table 2-6 for setting up your module in the mode you want. Your SCXI-1121 is shipped to you in the Voltage mode.

10kHz

Chapter 2 Configuration and Installation

•

W14

1 2 3

•

W15

1 2 3

•

W22

1 2 3

•

W23

1 2 3

•

W34

1 2 3

•

W35

1 2 3

•

W46

1 2 3

•

W47

1 2 3

Table 2-6.

Excitation

Channel

Jumpers

0 W14 and W15

1 W22 and W23

2 W34 and W35

3 W46 and W47

Voltage and Current Mode Excitation Jumper Setup

Voltage Mode

(Factory Setting)

W14

•

1 2 3

W22

•

1 2 3

W34

•

1 2 3

W46

•

1 2 3

•

1 2 3

•

1 2 3

•

W15

•

W23

•

W35

•

W47

•

Current Mode

1 2 3

Excitation Level

Each excitation channel of your SCXI-1121 has two different current or voltage levels. You can set a given channel to one of the following level modes:

• In the Current mode 0.150 or 0.450 mA

• In the Voltage mode 3.333 or 10 V

It is important to notice that you should select the level of excitation according to the load you are using. Table 2-7 lists the maximum load that can be driven per channel at each level of excitation for both volt and current excitation.

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Chapter 2 Configuration and Installation

•

W16

1 2 3

•

W26

1 2 3

•

W24

1 2 3

•

W25

1 2 3

•

W36

1 2 3

•

W37

1 2 3

•

W48

1 2 3

•

W49

1 2 3

Table 2-7. Maximum Load per Excitation Channel

Excitation Level Maximum Load

3.333 V 28 mA 10 V 14 mA

0.150 mA 10 kΩ

0.450 mA 10 kΩ

After selecting the excitation mode of operation desired—Voltage or Current—as described in the previous section, use Table 2-8 to set your SCXI-1121 for the level of operation. Your SCXI-1121 is shipped with the Voltage mode set to 3.333 V.

Table 2-8. Excitation Level Jumper Selection

Excitation

Channel

0 W16 and W26

1 W24 and W25

2 W36 and W37

3 W48 and W49

Jumpers

3.333 V or 0.150 mA (Factory Setting)

W16

•

1 2 3

W24

•

1 2 3

W36

•

1 2 3

W48

•

2 3

W25

•

1 2 3

W37

•

1 2 3

W49

•

W26

•

10 V or 0.450 mA

•

1 2 3

Chapter 2 Configuration and Installation

A B

W18

W17

1 2 3

•••

•

Using the Internal Half-Bridge Completion

Your SCXI-1121 includes half-bridge completion for half-bridge and quarter-bridge setups. The completion network consists of two

4.5 kΩ ± 0.05% ratio tolerance resistors with a temperature coefficient of 5 ppm/°C. These resistors are connected in series. To enable the network, you must set two jumpers for each input/excitation channel pair.

When the completion network is enabled, you cannot access the negative input of the amplifier, which preserves the overvoltage protection of the channel. Table 2-9 shows how to enable and disable the completion network.

Note

When using the half-bridge completion network with a quarter-bridge setup, you must use an extra resistor to complete the bridge. Place this resistor on the terminal block between the positive input channel and the negative excitation output.

Table 2-9.

Completion Network Jumpers

Channel Jumpers Enable Completion

0 W1 and W2

•••

•

A B

•

1 2 3

1 W17 and W18

•••

W18

•

A B

•

W17

1 2 3

Disable Network

(Factory Setting)

•••

•

A B

•

1 2 3

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Table 2-9. Completion Network Jumpers (Continued)

A B

W28

W27

1 2 3

•••

•

A B

W40

W39

1 2 3

•••

•

Channel Jumpers Enable Completion

Chapter 2 Configuration and Installation

Disable Network (Factory Setting)

2 W27 and W28

3 W39 and W40

•••

•

A B

•

1 2 3

•••

•

A B

•

1 2 3

W28

•

W40

•

W27

W39

Chapter 2 Configuration and Installation

Hardware Installation

You can install the SCXI-1121 in any available SCXI chassis. After you have made any necessary changes and have verified and recorded the jumper settings on the form in AppendixG, Technical Support Resources, you are ready to install the SCXI-1121. The following are general installation instructions consult the user manual or technical reference manual of your SCXI chassis for specific instructions and warnings.

1. Turn off the computer that contains the data acquisition board or disconnect it from your SCXI chassis.

2. Turn off the SCXI chassis. Do not insert the SCXI-1121 into a chassis that is turned on.

3. Insert the SCXI-1121 into the board guides. Gently guide the module into the back of the slot until the connectors make good contact. If a cable assembly has already been installed in the rear of the chassis, the module and cable assembly must be firmly engaged; however, do not force the module into place.

4. Screw the front mounting panel of the SCXI-1121 to the top and bottom threaded strips of your SCXI chassis.

5. If this module is to be connected to an MIO-16 data acquisition board, attach the connector at the metal end of the SCXI-1340 cable assembly to the rear signal connector on the SCXI-1121 module. Screw the rear panel to the rear threaded strip. Attach the loose end of the cable to the MIO-16 board.

Note

For installation procedures with other SCXI accessories and data acquisition boards,

consult Appendix E, SCXI-1121 Cabling.

6. Check the installation.

7. Turn on the SCXI chassis.

8. Turn on the computer or reconnect it to your chassis.

The SCXI-1121 module is installed and ready for operation.

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Signal Connections

This section describes the input and output signal connections to the SCXI-1121 board via the SCXI-1121 front connector and rear signal connector, and includes specifications and connection instructions for the signals given on the SCXI-1121 connectors.

Chapter 2 Configuration and Installation

Cautions

flammable gasses or fumes.

Keep away from live circuits. Do not remove equipment covers or shields unless you are trained to do so. If signal wires are connected to the device, hazardous voltages may exist even when the equipment is turned off. To avoid a shock hazard, do not perform procedures involving co ver or shield remo v al unless you are qualified to do so and disconnect all field power prior to removing covers or shields.

Equipment described in this document must be used in an Installation Category II environment per IEC 60664. This category requires local level supply mains-connected installation.

Do not operate damaged equipment. The safety protection features built into this device can become impaired if the device becomes damaged in any way . If the device is damaged, turn the device off and do not use until service-trained personnel can check its safety. If necessary , return the device to National Instruments for service and repair to ensure that its safety is not compromised.

Do not operate this equipment in a manner that contradicts the information specif ied in this document. Misuse of this equipment could result in a shock hazard.

Terminals are for use only with equipment that has no accessible live parts.

Do not substitute parts or modify equipment. Because of the danger of introducing additional hazards, do not install unauthorized parts or modify the device. Return the device to National Instruments for service and repair to ensure that its safety features are not compromised.

Do not operate the device in an explosive atmosphere or where there may be

When using the device with high common-mode voltages, you must insulate your signal wires for the highest input voltage. National Instruments is not liable for any damages or injuries resulting from inadequate signal wire insulation. Use only 26-14 AWG wire with a voltage rating of 300 V and 60 °C for measuring 250 V. Prepare your signal wire by stripping the insulation no more than 7 mm.

Chapter 2 Configuration and Installation

When connecting or disconnecting signal lines to the SCXI terminal block screw terminals, make sure the lines are powered off. Potential differences between the lines and the SCXI ground create a shock hazard while you connect the lines.

Connect the signal wires to the screw terminals by inserting the stripped end of the wire fully into the terminals. Tighten the terminals to a torque of 5 to 7 in.-lb.

Connections, including power signals to ground and vice versa, that exceed any of the maximum signal ratings on the SCXI device can create a shock or fi re hazard or can damage any or all of the boards connected to the SCXI chassis, the host computer, and the SCXI device. National Instruments is not liable for any damages or injuries resulting from incorrect signal connections.

If high voltages (≥30 Vrms and 42.4 V peak or 60 VDC) are present, you must connect a safety earth ground wire to the terminal block safety ground solder lug. This complies with safety agency requirements and protects against electric shock when the terminal block is not connected to the chassis. T o connect the safety earth ground to the safety ground solder lug, run an earth ground wire in the cable from the signal source to the terminal block. National Instruments is not liable for any damages or injuries resulting from inadequate safety earth ground connections.

Do not loosen or re-orient the safety ground solder lug hardware when connecting the safety ground wire. To do so reduces the safety isolation between the high voltage and safety ground.

Clean devices and terminal blocks by brushing off light dust with a soft, nonmetallic brush. Remove other contaminants with deionized water and a stiff nonmetallic brush. The unit must be completely dry and free from contaminants before returning to service.

Use only National Instruments TBX Series cable assemblies with high-voltage TBX Series terminal blocks.

Front Connector

Figure 2-3 shows the pin assignments for the SCXI-1121 front connector.

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Chapter 2 Configuration and Installation

Number

32 31 30 29 28 27 26 25 24 23 22 21 20 19 18 17 16 15 14 13 12 11 10

9 8 7 6 5 4 3 2 1

Signal

Name

CH0+

EX0+

EGND0

CH1+

EX1+

EGND1

CH2+

EX2+

EGND2

CH3+

EX3+

EGND3

SCAL

+5 V

CGND

Column

A B C

Signal Name

CH0–

EX0+

CH1–

EX1–

CH2–

EX2–

CH3–

EX3–

RSVD

MTEMP

DTEMP

Figure 2-3. SCXI-1121 Front Connector Pin Assignment

Chapter 2 Configuration and Installation

Front Connector Signal Descriptions

Pin Signal Name Description

A2 CGND Chassis Ground—This pin is tied to the SCXI chassis. C2 DTEMP Direct Temperature Sensor—This pin connects the

temperature sensor to the MCH4+ when the terminal block is configured for direct temperature connection.

A4 +5 V +5 VDC Source—This pin is used to power the

temperature sensor on the terminal block. 0.2 mA of source not protected.

C4 MTEMP Multiplexed Temperature Sensor—This pin connects the

temperature sensor to the output multiplexer.

A6 SCAL Shunt Calibration—This pin is tied to the SCAL bit and is

used to control the SCXI-1321 shunt calibration switch. CMOS/TTL output not protected.

C6, C8 RSVD Reserved—These pins are reserved. Do not connect any

signal to these pins.

A8, C10, C16, C22, C28

A10 EGND3 Excitation Ground 3—This pin connects to the excitation

A12 EX3+ Positiv e Excitation Output 3—This pin is connected to the

C12 EX3– Negative Excitation Output 3—This pin is connected to the

A14 CH3+ Positive Input Channel 3—This pin is connected to the

C14 CH3– Negative Input Channel 3—This pin is connected to the

A16 EGND2 Excitation Ground 2—This pin connects to the excitation

A18 EX2+ Positiv e Excitation Output 2—This pin is connected to the

C18 EX2– Negative Excitation Output 2—This pin is connected to the

No Connect Do not connect any signal to these pins.

ground 3 via a 51 kΩ resistor.

excitation channel 3 positive output.

excitation channel 3 negative output.

input channel 3 positive input.

input channel 3 negative input.

ground 2 via a 51 kΩ resistor.

excitation channel 2 positive output.

excitation channel 2 negative output.

SCXI-1121 User Manual 2-18 www.natinst.com

Chapter 2 Configuration and Installation

Pin Signal Name Description

A20 CH2+ Positive Input Channel 2—This pin is connected to the

input channel 2 positive input.

C20 CH2– Negative Input Channel 2—This pin is connected to the

input channel 2 negative input.

A22 EGND1 Excitation Ground 1—This pin connects to the excitation

ground 1 via a 51 kΩ resistor.

A24 EX1+ Positi v e Excitation Output 1—This pin is connected to the

excitation channel 1 positive output.

C24 EX1– Negative Excitation Output 1—This pin is connected to the

excitation channel 1 negative output.

A26 CH1+ Positive Input Channel 1—This pin is connected to the

input channel 1 positive input.

C26 CH1– Negative Input Channel 1—This pin is connected to the

input channel 1 negative input.

A28 EGND0 Excitation Ground 0—This pin connects to the excitation

ground 0 via a 51 kΩ resistor.

A30 EX0+ Positi v e Excitation Output 0—This pin is connected to the

excitation channel 0 positive output.

C30 EX0– Negative Excitation Output 0—This pin is connected to the

excitation channel 0 negative output.

A32 CH0+ Positive Input Channel 0—This pin is connected to the

input channel 0 positive input.

C32 CH0– Negative Input Channel 0—This pin is connected to the

input channel 0 negative input.

The signals on the front connector are all analog except pins A6, C6, and C8, which are digital controls. These analog signals can be divided into three groups—the analog input channels, the excitation channels, and the temperature sensor.

Chapter 2 Configuration and Installation

Analog Input Channels

The positive input channels are located in column A. Their corresponding negative input channels are located in column C. Each input corresponds to a separate amplifier and is fully isolated from the other channels and from earth ground. The inputs are designed in a floating single-ended configuration, hence the measured signal can be referenced to a ground level with common-mode voltage up to 250 V immunity, connect the negative input channel to the signal reference. If the measured signals are floating, connect the negative input channel to chassis ground on the terminal block. Figure 2-4 shows how to connect a ground-referenced signal. Figure 2-5 shows how to connect a floating signal. Figures 2-6 and 2-7 show how to connect AC-coupled signals.

. For better noise

rms

Figure 2-4.

Figure 2-5.

–

High

CMV

–

Module

out

–

Ground-Referenced Signal Connection with High Common-Mode Voltage

–

Module

out

–

Floating Signal Connection Referenced to Chassis Ground for Better

Signal-to-Noise Ratio

SCXI-1121 User Manual 2-20 www.natinst.com

Chapter 2 Configuration and Installation

bias

–

Module

out

–

Figure 2-6. Floating AC-Coupled Signal Connection

–

bias

High CMV

Module

out

–

Figure 2-7. AC-Coupled Signal Connection with High Common-Mode Voltage

For AC-coupled signals, you should connect an external resistor from the positive input channel to the signal reference. This is needed to provide the DC path for the positive input bias current. Typical resistor values range from 100 kΩ to 1 MΩ. This solution, although necessary in this case, lowers the input impedance of the input channel amplifier and introduces an additional offset voltage proportional to the input bias current and to the resistor value used. The typical input bias current of the amplif ier consists of ±80 pA and a negligible offset drift current. When a 100 kΩ resistor is used, this will result into ±8 µV of offset, which is insignificant in most applications. However, if larger resistors are used, significant input offset may result. To determine the maximum offset introduced by the biasing resistor, use the following equation:

ofsbiasIbiasRbias

The input signal range of an SCXI-1121 input channel is ±5 V/ G referenced to its negative input, where G

×=

is equal to the product of the

total

first-stage and second-stage gains. In addition, the input channels are overvoltage protected to 250 V

4.5 m

sink or source.

Arms

with power on or off at a maximum of

rms

Chapter 2 Configuration and Installation

Warning Exceeding the input signal range and the common-mode input range results in

distorted signals. Exceeding the maximum input voltage rating (250 V and negative terminals and between any terminal and earth ground) can damage the SCXI-1121, the SCXIbus, and the DAQ board. National Instruments is not liable for any damages or injuries resulting from such signal connections.

Excitation Channels

Four fully isolated excitation channels are available. Each excitation channel corresponds to an input channel. A 250 V between two corresponding channels (for example, between input channel 0 and excitation channel 0). In addition, the excitation outputs are overvoltage protected to 250 V

Warning Exceeding the overvoltage protection or isolation rating on the excitation output

can damage the SCXI-1121, the SCXIbus, and the DA Q board. National Instruments is not liable for any damages or injuries resulting from such signal connections.

Temperature Sensor Connection

Pins C2 and C4 are dedicated for connecting the temperature sensor to the SCXI-1121. The temperature sensor is not isolated and is referenced to chassis ground. The connection is overvoltage-protected to ±25 VDC with power on and ±15 VDC with power off.

rms

with current foldback.

rms

between positive

rms

isolation barrier exists

Warning Exceeding the overv oltage protection on the temperature connections can

damage the SCXI-1121, the SCXIbus, and the DAQ board. National Instruments is not liable for any damages resulting from such signal connections.

Connector-and-Shell Assembly

Two types of signal connectors are available to connect the transducers to the SCXI-1121 inputs. The first, the SCXI-1330 32-pin DIN C female connector-and-shell assembly, is available in a kit listed in the Optional

Equipment section in Chapter 1, Introduction. The connector has eyelet

ends for easy hook-and-solder wire connection. With this kit, you can build your own signal cable to connect to the SCXI-1121 inputs. After you have built the cable, the shell covers and protects the connector. Perform the following steps to assemble and mount the connector-and-shell assembly to your SCXI module:

1. Refer to Figure 2-8, Assembling and Mounting the SCXI-1330

Connector-and-Shell Assembly, and the diagram included with your

SCXI-1330 kit to build the connector-and-shell assembly.

2. Turn of f the computer that contains your DA Q board or disconnect the board from your SCXI chassis.

SCXI-1121 User Manual 2-22 www.natinst.com

Chapter 2 Configuration and Installation

3. Turn off your SCXI chassis.

4. Slide the selected module out of the SCXI chassis.

5. Remove the module cover.

6. Place one jack screw on the SCXI-1121 as indicated in Figure 2-8.

7. While holding the jack screw in place, insert the lock washe r and then the nut. Notice that you might need long-nose pliers to insert the washer and nut.

8. Tighten the nut by holding it firmly and rotating the jack screw.

9. Repeat steps 6 through 8 for the second jack screw.

10. Replace the module cover and tighten the grounding screw.

11. Slide the module back in place.

12. Connect the SCXI-1330 to your module connector and secure it by tightening both mounting screws.

Shell Assembly

Mounting Screw

Connector

Mounting Screw

Jack

Screws

Shell Assembly

Lock Washers

Nut

SCXI-1121 Module

Nut

Grounding Screw

Figure 2-8. Assembling and Mounting the SCXI-1330 Connector-and-Shell Assembly

Chapter 2 Configuration and Installation

SCXI-1320, SCXI-1328, and SCXI-1321 Terminal Blocks

The second type of connector available to connect the transducers to the SCXI-1121 inputs is a terminal block with an onboard temperature sensor and screw terminals for easy connection. One terminal block, the SCXI-1328 isothermal terminal block, has a high-accuracy onboard temperature sensor. The terminal block kits are listed in the Optional

Equipment section in Chapter 1, Introduction.

The terminal blocks consist of a shielded board with supports for connection to the SCXI-1121 input connector. The terminal blocks have 18 screw terminals for easy connection. Four pairs of screw terminals are for signal connection to the four inputs of the SCXI-1121, four pairs are for the excitation channels, and one pair of screw terminals connects to the chassis ground.

The following warnings contain important safety information concerning hazardous voltages and terminal blocks.

Warnings

insulate your signal wires appropriately. National Instruments is not liabl e for any damages or injuries resulting from inadequate signal wire insulation.

If high voltages (≥42 V strain-relief tab. This complies with UL 1244 and protects ag ainst electric shock when the terminal block is not connected to the chassis. To connect the safety earth ground to the strain-relief tab, run an earth ground wire in the cable from the signal source to the terminal block. National Instruments is not liable for any damages or injuries resulting from inadequate safety earth ground connections.

When using the terminal block with high common-mode voltages, you must

) are present, you must connect the safety earth ground to the

rms

SCXI-1320 and SCXI-1328 Terminal Blocks

When connecting your signals to the SCXI-1320 terminal block for use with the SCXI-1121, follow the labeling on the SCXI-1320 indicated under the module type column for the SCXI-1121 as indicated in Figure 2-11.

When connecting your signals to the SCXI-1328 high-accuracy isothermal terminal block for use with the SCXI-1121, follow the labeling on the SCXI-1328 indicated along the module type row for the SCXI-1121 as indicated in Figure 2-12.

SCXI-1121 User Manual 2-24 www.natinst.com

Chapter 2 Configuration and Installation

SCXI-1321 Offset-Null and Shunt-Calibration Terminal Block

The SCXI-1321 terminal block operates only with Revision C and later SCXI-1121 modules.

In addition to the 18 screw terminals, the SCXI-1321 has circuitry for offset-null adjust of Wheatstone bridges as well as a shunt resistor for strain-gauge shunt calibration. This terminal block works especially well with bridge-type transducers such as strain gauges. The SCXI-1321 can also easily accommodate thermocouples, RTDs, thermistors, millivolt sources, volt sources, and current-loop receivers.

SCXI-1321 Nulling Circuitry

The nulling circuitry operates with full-bridge, half-bridge, quarter-bridge, and strain-gauge configurations. Each channel has its own nulling circuitry and its own trimming potentiometer as listed in Table 2-10.

Table 2-10.

Trimmer Potentiometer and Corresponding Channel

Channel Number Trimmer Potentiometer

0 R1 1 R2 2 R14 3 R15

To null the static offset voltage of the bridge, use the following procedure:

1. Configure your bridge to the selected channel.

2. Select and read the channel output.

3. While monitoring the output, rotate the trimmer wiper with a flathead screwdriver until you reach 0 V.

You have nulled your bridge and are ready for a measurement. The nulling range for your terminal block is ±2.5 mV, assuming that you

have a 120 Ω strain gauge and 3.333 V excitation voltage. You can change this range by replacing the nulling resistor with a resistor of another value. Each channel has an independent nulling resistor. You can therefore mix your ranges to accommodate each channel requirement. T able 2-11 lists the nulling resistors and their corresponding channels.

Chapter 2 Configuration and Installation

The value of all the nulling resistors on your terminal block is 39 kΩ. Notice that these resistors are socketed for easy replacement. These sockets best fit a 1/4 W resistor lead size.

To determine your nulling range, use the following formula (refer to Figure 2-9 for visual help):

Table 2-11. Nulling Resistors and Corresponding Channel

Channel Number Nulling Resistor

0 R3 1 R5 2 R7 3 R9

nullingrange

exc

--------- 2

excRdRnullRg

---------------------------------------------------------- -–±=

nullRgRdRnullRg

+()

where

is the nominal strain-gauge resistance value.

is either a completion resistor or a second strain-gauge nominal

resistance.

is the nulling resistor value.

null

is the excitation voltage (3.333 or 10 V).

exc

For example, assuming:

= 3.333 V

exc

= 120 Ω

= 39 kΩ

null

= ±2.56 mV

nulling

+()+

SCXI-1121 User Manual 2-26 www.natinst.com

Chapter 2 Configuration and Installation

Assuming a strain-gauge range with a gauge factor of GF = 2 and a quarter-bridge configuration, this range corresponds to ±1,498 µε as given by the strain formula for a quarter-bridge strain-gauge configuration:

–4V

-------------------------------=

GF 12Vr+()

where

strained voltage static unstrained voltage–

------------------------------------------------------------------------------------------------------- -=

exc

EX+

Trimmer

Potentiometer

SCXI-1321

null

CH+ CH–

EX–

Figure 2-9. Nulling Circuit

Using the SCXI-1321 with RTDs and Thermistors

When using this terminal block with RTDs or thermistor-type transducers and with the SCXI-1121 excitation set in the Current mode, you must disable the nulling circuit of the channel of interest. You can do this in two steps:

1. Place the enable/disable jumper in position D (disable) as shown in Table 2-12.

2. Remove the nulling resistor from its sockets.

Chapter 2 Configuration and Installation

Jumper Position Description

Table 2-12. Jumper Settings of the Nulling Circuits

•

Nulling circuit of Channel 0 is enabled; factory setting

Nulling circuit of Channel 0 is disabled

Nulling circuit of Channel 1 is enabled; factory setting

Nulling circuit of Channel 1 is disabled

Nulling circuit of Channel 2 is enabled; factory setting

Nulling circuit of Channel 2 is disabled

Nulling circuit of Channel 3 is enabled; factory setting

Nulling circuit of Channel 3 is disabled

SCXI-1121 Shunt Calibration

Shunt calibration circuits are independent from each other but are controlled together. In other words, when SCAL is set to 1 on the SCXI-1121, all the shunt switches close when SCAL is cleared to 0, all the switches open. At startup or reset, all switches are open. This shunt calibration circuitry configuration places a shunting resistor in parallel with the strain gauge as shown in Figure 2-10.

SCXI-1121 User Manual 2-28 www.natinst.com

SCAL

Chapter 2 Configuration and Installation

EX+

CH+ CH–

EX–

SCXI-1321

SCAL

Figure 2-10. Shunt Circuit

The shunting resistors R a resistor of another value to achieve the required changes. The R

are socketed so that you can replace them with

SCAL

resistors on your terminal block have a 301 kΩ ±1% value. Assuming a quarter-bridge strain-gauge configuration with a gauge factor

of GF = 2, the equiva lent strain change introduced by the R

SCAL

shunting

resistor is –199 µε. Determine the change as follows:

1. Determine the change caused by the shunting resistor using the following formula:

change

excRdRSCALRg

---------------------------------------------------------- -

SCALRdRSCALRg

+()

+()+

exc

--------- -–= 2

2. Using the appropriate strain-gauge strain formula, and assuming that you have no static voltage, determine the equivalent strain that the

should produce. For example, R

SCAL

= 301 kΩ and a

SCAL

quarter-bridge 120 Ω strain gauge with a gauge factor of GF = 2 and V

= 3.333 V and R = 120 Ω produces the following result:

exc

= 0.3321 mV

change

Replacing the strained voltage with V

in the quarter-bridge strain

change

equation produces an equivalent –199 µε of change.

Chapter 2 Configuration and Installation

Terminal Block Temperature Sensor

To accommodate thermocouples with the SCXI-1121, the terminal block has an onboard temperature sensor for cold-junction compensation. You can connect this temperature sensor in two ways:

• You can connect the temperature sensor to the MTEMP pin (C4) on the module front connector and multiplex the sensor at the output multiplexer along with the amplifier outputs. This is the Multiplexed T emperature Sensor (MTS) mode. Refer to the Configuration Register section in Chapter 4, Register Descriptions, for further details.

• You can connect the temperature sensor to a separate data acquisition channel via MCH4± (pins 11 and 12 on the module rear signal connector). This is the Direct Temperature Sensor (DTS) mode.

Note

Use an average of a large number of samples to obtain the most accurate reading.

Noisy environments require more samples for greater accuracy.

The SCXI-1320 and SCXI-1321 temperature sensors output 10 mV/°C and have an accuracy of ±1 °C over the 0 to 55 °C temperature range. To determine the temperature, use the following formulas:

where V

TEMPOUT

T °C() 100 V

T °F()

is the temperature sensor output and T (°F) and T (°C) are

()=

TEMPOUT

T °C()[]9

---------------------- - 32+= 5

the temperature readings in degrees Fahrenheit and degrees Celsius, respectively.

The SCXI-1328 temperature sensor outputs 0.62 to 0.07 V from 0 to 55 °C and has an accuracy of ±0.35 °C over the 15 to 35 °C range and ±0.65 °C over the 0 to 15 °C and 35 to 55 °C ranges. To determine the temperature, use the following formulas:

where T

T °C() T

is the temperature in kelvin

273.15–=

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Chapter 2 Configuration and Installation

ln()cR

ln()

a = 1.288 x 10 b = 2.356 x 10 c = 9.556 x 10

--------------------------------------------------------------=

ab R

++[]

–3

–4

–8

RT = resistance of the thermistor in Ω

TEMPOUT



------------------------------------- -



2.5 V

–

TEMPOUT

T °C()[]9

---------------------- - 32+= 5

TEMPOUT

50,000

= output voltage of the temperature sensor

T °F()

where T (°F) and T (°C) are the temperature readings in degrees Fahrenheit and degrees Celsius, respectively.

Terminal Block Jumper Configuration

In addition to the screw terminals, the terminal block has one jumper for configuring the onboard temperature sensor. When you set jumper W1 on the SCXI-1320 or SCXI-1328 (jumper W5 on the SCXI-1321) to the MTEMP position, the jumper connects the temperature sensor output to the SCXI-1121 output multiplexer. This is the factory setting. The DTEMP position of jumper W1 (jumper W5 on the SCXI-1321) connects the temperature sensor to the SCXI-1121 MCH4+ signal on the rear signal connector.

In both MTS and DTS modes, the reference to the temperature sensor signal is the SCXI-1121 analog ground that is connected to MCH0– in the MTS mode and to MCH4– in the DTS mode. Notice that MCH4– is continuously connected to the SCXI-1121 ground, whereas MCH0– is switched through the output multiplexer.

One jumper block comprises both positions; therefore, you can use only one type of configuration at a time. The parking position for the jumper block is in the MTEMP position (the temperature sensor is disabled until the RTEMP bit in the Configuration Register selects the sensor).

Chapter 2 Configuration and Installation

Ta bles 2-13, 2-14 , and 2-15 show the jumper settings on the SCXI-1320, SCXI-1328, and SCXI-1321 terminal blocks.

Jumper Position Description

Table 2-13. Jumper Settings on the SCXI-1320 Terminal Block

W1 MTS mode selected; factory

•

MTEMP

•

DTEMP

setting; parking position

W1 DTS mode selected

•

MTEMP

•

DTEMP

Table 2-14. Jumper Settings on the SCXI-1328 Terminal Block

Jumper Position Description

W1 MTS mode selected; factory

DTEMP MTEMP

•••

•

setting; parking position

W1 DTS mode selected

DTEMP MTEMP

Table 2-15. Jumper Settings on the SCXI-1321 Terminal Block

•••

•

Jumper Position Description

W5 MTS mode selected;

MTEMP

•••

•

DTEMP

factory setting; parking position

W5 DTS mode selected

•••

•

MTEMP

SCXI-1121 User Manual 2-32 www.natinst.com

DTEMP

Terminal Block Signal Connection

Chapter 2 Configuration and Installation

Warnings

The chassis GND terminals on your terminal block are for grounding high impedance sources such as a floating source (1 mA maximum). Do not use these terminals as safety earth grounds.

If high voltages (≥42 V

) are present, you must connect the safety earth ground to the

rms

strain-relief tab. This complies with UL 1244 and fully protects against electric shock when the terminal block is not connected to the chassis. To connect the safety earth ground to the strain-relief tab, run an earth ground wire in the cable from the signal source to the terminal block. National Instruments is not liable for any damages or injuries resulting from inadequate safety earth ground connections.

Shock Hazard—This unit should only be opened by qualified personnel aware of the dangers involved. Disconnect all power before removing cover. Always install grounding screw.

To conn ect the signal to the terminal block, use the following procedure:

1. Remove the grounding screw of the top cover.

2. Snap out the top cover of the shield by placing a screwdriver in the groove at the bottom of the terminal block.

3. Slide the signal wires, one at a time, through the front panel strain-relief opening. You can add padding or insulation if necessary.

4. Connect the wires to the screw terminals. For thermistor and RTD connection, follow the procedure stated in the Using the SCXI-1321

with RTDs and Thermistors section earlier in this chapter.

5. Tighten the larger strain-relief screws.

6. Snap the top cover back in place.

7. Reinsert the grounding screw to ensure proper shielding.

8. Connect the terminal block to the SCXI-1121 front connector as explained in the Terminal Block Installation section later in this chapter.

Figure 2-11 shows a parts locator diagram for the SCXI-1320 terminal block. Figure 2-12 shows a parts locator diagram for the SCXI-1328 terminal block. Figure 2-13 shows a parts locator diagram for the SCXI-1321 terminal block.

Chapter 2 Configuration and Installation

Figure 2-11. SCXI-1320 Parts Locator Diagram

SCXI-1121 User Manual 2-34 www.natinst.com

Chapter 2 Configuration and Installation

Figure 2-12. SCXI-1328 Parts Locator Diagram

Chapter 2 Configuration and Installation

Figure 2-13. SCXI-1321 Parts Locator Diagram

Terminal Block Installation

To connect the terminal block to the SCXI-1121 front connector, perform the following steps:

1. Connect the SCXI-1121 front connector to its mating connector on the terminal block.

2. Make sure that the SCXI-1121 top and bottom thumbscrews do not obstruct the rear panel of the terminal block.

3. Tighten the top and bottom screws on the back of the terminal block to hold it securely in place.

SCXI-1121 User Manual 2-36 www.natinst.com

Rear Signal Connector

Note

If you are using the SCXI-1121 with a National Instruments data acquisition board and cable assembly , you do not need to read the remainder of this chapter . If you are using the SCXI-1180 feedthrough panel, the SCXI-1343 rear screw terminal adapter, or the SCXI-1351 one-slot cable extender with the SCXI-1121, you should read this section.

Figure 2-14 shows the pin assignments for the SCXI-1121 rear signal connector.

Chapter 2 Configuration and Installation

AOGND

MCH0+ MCH1+

MCH2+

MCH3+

MCH4+

OUTREF

SERDATIN

DAQD*/A

SLOT0SEL*

DIG GND

SERCLK

RSVD

12 34 56 78

910 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50

AOGND MCH0– MCH1– MCH2– MCH3– MCH4–

DIG GND SERDATOUT

SCANCLK

Figure 2-14.

SCXI-1121 Rear Signal Connector Pin Assignment

Chapter 2 Configuration and Installation

Rear Signal Connector Signal Descriptions

Pin Signal Name Description

1-2 AOGND Analog Output Ground—These pins are connected to the analog

reference when jumper W33 is in position AB-R0.

3-12 MCH0± through

MCH4±

Analog Output Channels 0 through 4—Connects to the data acquisition board differential analog input channels.

19 OUTREF Output Reference—This pin serves as the reference node for the

analog channels output in the Pseudodifferential Reference mode. It should be connected to the analog input sense of the NRSE data acquisition board.

24, 33 DIG GND Digital Ground—These pins supply the reference for data

acquisition board digital signals and are tied to the module digital ground.

25 SERDATIN Serial Data In—This signal taps into the SCXIbus MOSI line to

provide serial input data to a module or Slot 0.

26 SERDATOUT Serial Data Out—This signal taps into the SCXIbus MISO line to

accept serial output data from a module.

27 DAQD*/A Data Acquisition Board Data/Address Line—This signal taps into

the SCXIbus D*/A line to indicate to the module whether the incoming serial stream is data or address information.

29 SLOT0SEL* Slot 0 Select—This signal taps into the SCXIbus INTR* line to

indicate whether the information on MOSI is being sent to a module or Slot 0.

36 SCANCLK Scan Clock—This indicates to the SCXI-1121 that a sample has

been taken by the data acquisition board and causes the SCXI-1121 to change channels. See the Timing Requirements and

Communication Protocol section later in this chapter for more

detailed information on timing.

37 SERCLK Serial Clock—This signal taps into the SCXIbus SPICLK line to

clock the data on the MOSI and MISO lines. See the Timing

Requirements and Communication Protocol section later in this

chapter for more detailed information on timing.

43 RSVD Reserved.

All other pins are not connected.

SCXI-1121 User Manual 2-38 www.natinst.com

Chapter 2 Configuration and Installation

The signals on the rear signal connector can be classified as analog output signals, digital I/O signals, or timing I/O signals. Signal connection guidelines for each of these groups are given in the following section.

Analog Output Signal Connections

Pins 1 through 12 and pin 19 of the rear signal connector are analog output signal pins. Pins 1 and 2 are AOGND signal pins. AOGND is an analog output common signal that is routed through jumper W33 to the analog reference on the SCXI-1121. You can use these pins for a general analog power ground tie point to the SCXI-1121 if necessary. In particular, when using differential input data acquisition boards such as the MIO-16 series, it is preferable to leave jumper W33 in its factory setting or in position AB-R1 to avoid ground loops. With data acquisition boards that are configured for referenced single-ended (RSE) measurements, W33 should be in position AB-R0 to connect the SCXI-1121 ground to the data acquisition analog ground. Pin 19 is the OUTREF pin this pin is connected internally to the analog reference when jumper W33 is in position AB-R2. Pins 3 through 12 are the analog output channels of the SCXI-1121. Pins 3 and 4 or MCH0± are a multiplexed output of all four input channels and the temperature sensor output. Pins 5 through 10 or MCH1± through MCH3± are a parallel connection of input channels 1 through 3 to the rear signal connector. Pins 11 and 12 or MCH4± are a direct connection of the temperature sensor. Notice that the temperature sensor is located on the terminal block. For further details on configuring the temperature sensor output, refer to the SCXI-1320, SCXI-1328, and SCXI-1321

Terminal Blocks section earlier in this chapter.

Warning

The SCXI-1121 analog outputs are not overv oltage-protected. Applying external voltages to these outputs can damage the SCXI-1121. National Instruments is not liable for any damages resulting from such signal connections.

Note

The SCXI-1121 analog outputs are short-circuit protected.

Chapter 2 Configuration and Installation

Digital I/O Signal Connections

Pins 24 through 27, 29, 33, 36, 37, and 43 constitute the digital I/O lines of the rear signal connector. They are divided into three categories—the digital input signals, the digital output signals, and the digital timing signals.

The digital input signals are pins 24, 25, 27, 29, 33, and 37. The data acquisition board uses these pins to configure an SCXI module that is under data acquisition board control. Each digital line emulates the SCXIbus communication signals as follows:

• Pin 25 is SERDATIN and is equivalent to the SCXIbus MOSI serial data input line.

• Pin 27 is DAQD*/A and is equivalent to the SCXIbus D*/A line. It indicates to the module whether the incoming serial stream on SERDATIN is data (DAQD*/A = 0), or address (DAQD*/A = 1) information.

• Pin 29 is SLO T0SEL* and is equi va lent to the SCXIbus INTR* line. It indicates whether the data on the SERDATIN line is being sent to Slot 0 (SLOT0SEL* = 0) or to a module (SLOT0SEL* = 1).

• Pins 24 and 33 are the digital ground references for the data acquisition board digital signals and are tied to the module digital ground.

• P in 37 is SERCLK and is equiv alent to the SCXIb us SPICLK line and is used to clock the serial data on the SERDATIN line into the module registers.

The digital output signal is pin 26.

• Pin 26 is SERDATOUT and is equivalent to SCXIbus MISO when jumper W38 is in position 1.

The digital input and output signals of the SCXI-1121 match the digital I/O lines of the MIO-16 board. When used with an SCXI-1341, SCXI-1342, or SCXI-1344 cable assembly, the SCXI-1121 signals match the digital lines of the Lab-NB/Lab-PC/Lab-PC+/Lab-LC boards and the PC-LPM-16 board, respectively. Table 2-16 lists the equivalences. For more information, consult Appendix E, SCXI-1121 Cabling.

SCXI-1121 User Manual 2-40 www.natinst.com

Chapter 2 Configuration and Installation

Table 2-16. SCXIbus to SCXI-1121 Rear Signal Connector to Data Acquisition Board Pin Equivalences

SCXI-1121

SCXIbus Line

Rear Signal

Connector

MIO-16

Lab-NB/Lab-PC

Lab-PC+/Lab-LC

PC-LPM-16

MOSI SERDATIN ADIO0 PB4 DOUT4

D*/A DAQD*/A ADIO1 PB5 DOUT5

INTR* SLOT0SEL* ADIO2 PB6 DOUT6

SPICLK SERCLK EXTSTROBE* PB7 DOUT7

MISO SERDATOUT BDIO0 PC1 DIN6

The digital timing signals are pins 36 and 43.

• Pin 36 is used as a clock by the SCXI-1121 to increment the MUXCOUNTER after each conversion by the data acquisition board during scanning. This signal is referred to as SCANCLK. See Chapter 3, Theory of Operation, for a description of MUXCOUNTER.

• Pin 43 is a reserved digital input.

The following specifications and ratings apply to the digital I/O lines.

Absolute maximum voltage

Input rating 5.5 V with respect to DIG GND

Digital input specifications (referenced to DIG GND):

input logic high voltage 2 V minimum

input logic low voltage 0.8 V maximum

input current leakage ±1 µA maximum

Digital output specifications (referenced to DIG GND):

output logic high voltage 3.7 V minimum at 4 mA maximum

output logic low voltage 0.4 V maximum at 4 mA maximum

Chapter 2 Configuration and Installation

Timing Requirements and Communication Protocol

Timing Signal

The data acquisition timing signal is SCANCLK. SCANCLK is used to increment MUXCOUNTER on its rising edge.

Figure2-15 shows the timing requirements of the SCANCLK signal. These requirements will ensure that SCANCLK is properly transmitted over TRIG0.

SCANCLK

low

high

low

high

Time low before rising edge 400 nsec minimum Time high before falling edge 250 nsec minimum

Figure 2-15.

SCANCLK Timing Requirements

For output selection time specifications, refer to AppendixA,

Specifications.

Communication Signals

This section describes the methods for communicating on the Serial Peripheral Interface (SPI) bus and their timing requirements. The communication signals are SERDATIN, DAQD*/A, SLOT0SEL*, SERDATOUT, and SERCLK. Furthermore, SS* is produced by Slot 0 according to data acquisition board programming, and SS* timing relationships will also be discussed. For information on the Slot 0 Slot-Select Register, consult Chapter 4, Register Descriptions.

The data acquisition board determines to which slot it will talk by writing a slot-select number to Slot 0. In the case of an SCXI-1001 chassis, this write also determines to which chassis the data acquisition board will talk. Writing a slot-select number is also used in programming the Slot 0 hardscan circuitry. See Chapter 5, Programming, for information on programming the Slot 0 hardscan circuitry.

The following sections detail the procedure for selecting a slot in a particular chassis. Figure2-16 illustrates the timing of this procedure with the example case of selecting Slot 11 in Chassis 9. Notice that the factory-default chassis address for the SCXI-1000 is address 0. For information on changing the address of your chassis, consult the SCXI-1000/1001 User Manual. An SCXI-1000 chassis will respond to any chassis number.

SCXI-1121 User Manual 2-42 www.natinst.com

SLOT0SEL*

SS*X

Chassis Y

SS*11

Chassis 9 SERCLK

SERDATIN

ss_dis

clk_wait

Chapter 2 Configuration and Installation

slot0sel*_wait

0100 110 11

Chassis ID = 9 Slot 11

ss_en

ss _ dis

clk _ wait

slot0sel* _ wait

ss _ en

SLOT0SEL* low to SS* disabled 200 nsec maximum SLOT0SEL* low to first rising edge on SERCLK 75 nsec minimum Last rising edge on SERCLK to SLOT0SEL* high 250 nsec minimum SLOT0SEL* high to SS* enabled 350 nsec maximum

Figure 2-16. Slot-Select Timing Diagram

To write the 16 -bit slot-select number to Slot 0, follow these steps:

1. Initial conditions: SERDATIN = don't care DAQD*/A = don't care SLOT0SEL* = 1 SERCLK = 1

2. Clear SLOT0SEL* to 0. This will deassert all SS* lines to all modules in all chassis.

3. For each bit, starting with the most significant bit, perform the following action:

a. SERDATIN = bit to be sent. These bits are the data that is being

written to the Slot-Select Register. b. SERCLK = 0 c. SERCLK = 1. This rising edge clocks the data.

4. Set SLOT0SEL* to 1. This will assert the SS* line of the module whose slot number was written to Slot 0. If multiple chassis are being used, only the appropriate slot in the chassis whose address corresponds to the written chassis number will be selected. When no communication is taking place between the data acquisition board and any modules, it is recommended that 0 be written to the Slot-Select Register to ensure that no accidental writes occur.

Chapter 2 Configuration and Installation

Figure 2-17 shows the timing requirements on the SERCLK and SERDATIN signals. You must observe these timing requirements for all communications. T

SERCLK

SERDATIN

SERDATOUT

delay

is a specification of the SCXI-1121.

delay

low

setup

high

hold

T T T T T

low high setup hold delay

Minimum low time 65 nsec minimum Minimum high time 400 nsec minimum SERDATIN setup time 200 nsec minimum SERDATIN hold time 200 nsec minimum SERDATOUT delay 350 nsec maximum

Figure 2-17. Serial Data Timing Diagram

After the Slot-Select line to an SCXI-1121 has been asserted, you can write to its Configuration Register and read from its Module ID Register by following the protocols given below. The contents of the Module ID Register are reinitialized by deasserting Slot-Select. After the 32 bits of data are read from the Module ID Register, further data will be zeros until reinitialization occurs.

To write to the Configuration Register, follow these steps:

1. Initial conditions: SS* asserted low SERDATIN = don't care DAQD*/A = 0 (indicates data will be written to Configuration

2. For each bit to be written: Establish the desired SERDATIN level corresponding to this bit. SERCLK = 0 SERCLK = 1. Clock the data.

SCXI-1121 User Manual 2-44 www.natinst.com

Chapter 2 Configuration and Installation

3. Pull SLOT0SEL* low to deassert the SS* line and establish conditions for writing a new slot-select number to the Slot 0 Slot-Select Register.

4. If you are not selecting another slot, you should write zero to the Slot 0 Slot-Select Register.

Figure 2-18 illustrates a write to the SCXI-1121 Configuration Register of the binary pattern:

10000011 00001111

SLOT0SEL*

SS*

SERCLK

SERDATIN

Figure 2-18. Configuration Register Write Timing Diagram

01 00001100001111

To read from the Module ID Register, follow these steps:

1. Initial conditions: SS* asserted low SERDATIN = don't care DAQD*/A = 1. Make sure DAQD*/A does not go low or erroneous

data will be written to the Configuration Register. SLOT0SEL* = 1 SERCLK = 1 (and has not changed since SS* went low)

2. For each bit to be read: SERCLK = 0 SERCLK = 1. Clock the data. Read the level of the SERDATOUT line.

3. Pull SLOT0SEL* low to deassert the SS* line and establish conditions for writing a new slot- select number to the Slot 0 Slot-Select Register.

4. If you are not selecting another slot, you should write zero to the Slot 0 Slot-Select Register.

Chapter 2 Configuration and Installation

Figure 2-19 illustrates a read of the SCXI-1121 Module ID Register.

SLOT0SEL*

SS*

SERCLK

SERDATOUT

delay

000000 00000000000000000000000001

byte 0 = 2 byte 3 = 0byte 2 = 0byte 1 = 0

For further details on programming these signals, refer to Chapter 5,

Programming.

delay

SS* high to SERDATOUT high 350 nsec maximum

Figure 2-19. SCXI-1121 Module ID Register Timing Diagram

SCXI-1121 User Manual 2-46 www.natinst.com

Theory of Operation

This chapter contains a functional overview of the SCXI-1121 module and explains the operation of each functional unit making up the SCXI-1121.

Functional Overview

The block diagram in Figure 3-1 illustrates the key functional components of the SCXI-1121.

SCXIbus

Isolated Section

–

Front Connector

–

•

–

Nonisolated

Section

Input channel 0

Excitation 0

Input channel 3

Excitation 3

Temperature sensor

Figure 3-1.

Digital

Interface

and

Control

•

SCXI-1121 Block Diagram

Timing

and Analog Output

Stage

Rear Signal Connector

Chapter 3 Theory of Operation

The major components of the SCXI-1121 are as follows:

• SCXIbus connector

• Digital interface

• Digital control circuitry

• Timing and analog circuitry The SCXI-1121 consists of four isolated amplifier channels with gains of

1, 2, 5, 10, 20, 50, 100, 200, 500, 1,000, and 2,000, and four isolated excitation channels with voltage or current excitation. The SCXI-1121 also has a digital section for automatic control of channel scanning, for temperature selection, and for MUXCOUNTER clock selection.

The theory of operation for each of these components is explained in the rest of this chapter.

SCXI-1121 User Manual 3-2 www.natinst.com

SCXIbus Connector

Chapter 3 Theory of Operation

Figure 3-2 shows the pin assignments for the SCXIbus connector.

GUARD GUARD GUARD

AB0+ GUARD GUARD GUARD

GUARD GUARD GUARD

RESET*

MISO

V–

V– CHSGND CHSGND

V+ V+

+5 V

SPICLK

TRIG0

SS*

A1 B1 A2 B2 A3 B3 A4 B4 A5 B5 A6 B6 A7 B7 A8 B8 A9 B9 A10 B10 A11 B11 A12 B12 A13 B13 A14 B14 A15 B15 A16 B16 A17 B17 A18 B18 A19 B19 A20 B20 A21 B21 A22 B22 A23 B23 A24 B24

D1 C1 D2 C2 D3 C3 D4 C4 D5 C5 D6 C6 D7 C7 D8 C8 D9 C9 D10 C10 D11 C11 D12 C12 D13 C13 D14 C14 D15 C15 D16 C16 D17 C17 D18 C18 D19 C19 D20 C20 D21 C21 D22 C22 D23 C23 D24 C24

GUARD GUARD GUARD

AB0– GUARD GUARD GUARD

GUARD GUARD GUARD

CHSGND CHSGND CHSGND CHSGND CHSGND

RSVD

INTR* D*/A

V–

V– CHSGND CHSGND

V+

+5 V

MOSI

SCANCON

Figure 3-2.

SCXIbus Connector Pin Assignment

Chapter 3 Theory of Operation

SCXIbus Connector Signal Descriptions

Pin Signal Name Description

A1, B1, C1, D1, A2, D2,A3, B3, C3, D3, A4, D4, A5, B5, C5, D5, A6, D6

B2 AB0+ Analog Bus 0+ —Positive analog bus 0 line. Used

C2 AB0– Analog Bus 0– —Negative analog b us 0 line. Used

C13-C17, A21, B21, C21, D21

C18 RSVD Reserved. A19 RESET* Reset—When pulled low, reinitializes the module

B19 MISO Master-In Slave-Out—Transmits data from the

C19 D*/A Data/Address—Indicates to the module whether

D19 INTR* Interrupt—Active low. Causes data that is on

GUARD Guard—Shields and guards the analog bus lines

from noise.

to multiplex several modules to one analog signal.

CHSGND Chassis Ground—Digital and analog ground

reference.

to its power-up state. Totem pole. Input.

module to the SCXIbus. Open collector. I/O.

address information or data information is being sent to the module on MOSI. Open collector. I/O.

MOSI to be written to the Slot-Select Register in

Slot 0. Open collector. Output. A20, B20, C20, D20 V– Negative Analog Supply— –18.5 to –25 V. A22, B22, C22, D22 V+ Positive Analog Supply— +18.5 to +25 V. A23, D23 +5 V +5 VDC Source—Digital power supply. B23 SPICLK Serial Peripheral Interface (SPI) Clock—Clocks

the serial data on the MOSI and MISO lines. Open

collector. I/O. C23 MOSI Master-Out Slave-In—Transmits data from the

SCXIbus to the module. Open collector. I/O.

SCXI-1121 User Manual 3-4 www.natinst.com

Chapter 3 Theory of Operation

Pin Signal Name Description

A24 TRIG0 TRIG0—General-purpose trigger line used by the

SCXI-1121 to send SCANCLK to other modules or receive SCANCLK from other modules. Open collector. I/O.

B24 SS* Slot Select—When low, enables module

communications over the SCXIbus. Totem pole. Input.

C24 SCANCON Scanning Control—Combination output enable

and reload signal for scanning operations. Totem pole. Input.

All other pins are not connected.

MOSI, MISO, SPICLK, and SS* form a synchronous communication link that conforms with SPI using an idle-high clock and second-edge data latching. D*/A, INTR*, and RESET* are additional control signals.

When the module is being used in an SCXI-1000 or SCXI-1001 chassis, the data acquisition board, via the module rear signal connector, must tap into the open-collector backplane signal lines as a master to write to the module. The signal connections from the rear signal connector to the backplane are shown in Table 3-1.

Table 3-1. SCXIbus Equivalents for the Rear Signal Connector

Rear Signal

Connector Signal

SCXIbus Equivalent

SERDATIN MOSI DAQD*/A D*/A SLOT0SEL* INTR* Jumper W44 must be set to position 1 SERCLK SPICLK SERDATOUT MISO Jumper W38 must be set to position 1

The SCXI-1121 module converts the data acquisition board signals to open-collector signals on the backplane of the SCXI chassis. In order for the data acquisition board to talk to a slot, the board must first assert the SS* for that slot. This is done by asserting INTR* low, writing a 16-bit number over MOSI corresponding to the desired slot (and chassis if an SCXI-1001

Chapter 3 Theory of Operation

chassis is being used), and then releasing INTR* high. At this point, SS* of the desired slot is asserted low and the data acquisition board can communicate with the module in that slot according to the SPI protocol.

Digital Interface

Figure 3-3 shows a diagram of the SCXI-1121 and SCXIbus digital interface circuitry.

Buffered Serial Data

Buffered Digital Signal Controls

MISO

SCXIbus

INTR*

SPICLK

Digital

Interface

D*/A

MOSI

SS*

SERDATIN

DAQD*/A

SLOT0SEL*

SERCLK

Rear Signal Connector

SERDATOUT

Figure 3-3.

Digital Interface Circuitry Block Diagram

The digital interface circuitry is divided into a data acquisition section and an SCXIbus section. The SCXI-1121 connects to the SCXIbus via a 4 × 24 metral receptacle and to the data acquisition board via a 50-pin ribbon-cable header. The digital interface circuitry buffers the digital signals from the data acquisition board and from the SCXIbus and sends signals back and forth between the data acquisition board and the SCXIbus.

SCXI-1121 User Manual 3-6 www.natinst.com

Digital Control Circuitry

Figure 3-4 diagrams the SCXI-1121 digital control.

Chapter 3 Theory of Operation

Serial Data Out

Input Channel Select

Module ID Register

Buffered

Configuration

Output

Stage

Control

Figure 3-4.

SCANCLK

Path

Control

Hardware

Scan

Control

SCXI-1121 Digital Control

Serial Data In Buffered Digital

Control Signals

The digital control section consists of the Configuration Register and the Module ID Register.

The Configuration Register is a two-byte, serial-in parallel-out shift register. Data is received on the MOSI line from either Slot 0 or the data acquisition board when SS* is enabled and D*/A indicates data transfer (D*/A low). The Configuration Register provides temperature channel selection and channel selection, and configures the SCXI-1121 for scanning options. All the control bits are fed into a latch before being routed to the rest of the module. The channel-select bits are taken directly from the shift register. Complete descriptions of the register bits are given in Chapter 4, Register Descriptions. Writes to the Configuration Register require the following steps:

1. SS* goes low, enabling communication with the board.

2. D*/A goes low, indicating that the information sent on the MOSI line is data.

Chapter 3 Theory of Operation

3. The serial data is available on MOSI and SPICLK clocks it into the register.

4. SS* goes high and D*/A goes high, indicating an end of communication. This action latches the Configuration Register bits.

When the SCXIbus is reset, all bits in the Configuration Register are cleared.

The Module ID Register connects to MISO on the SCXIbus. The Module ID Register is an 8-bit parallel/serial-in serial-out shift register and an SPI communication adapter. The contents of the Module ID Register are written onto MISO during the first four bytes of transfer after SS* has been asserted low. Zeros are written to MISO thereafter until SS* is released and reasserted. The SCXI-1121 module ID is hex 00000002.

Analog and Timing Circuitry

The SCXIbus provides analog power (±18.5 VDC) that is regulated on the SCXI-1121 to ±15 VDC, a guard, an analog bus (AB0±), and a chassis ground (CHSGND). AB0± buses the SCXI-1121 output to other modules or receives outputs from other modules via the SCXIbus. Refer to the

Calibration section later in this chapter for more information. The guard

guards the analog bus, and can be connected via jumper W33 to the analog ground reference or can be left floating (a connection can be made by another board).

The data acquisition board analog input and timing is the interface between the SCXI-1121 output and the data acquisition board. This is fully described in the following section.

Analog Input Channels

Figure 3-5 is a diagram of the analog input block.

SCXI-1121 User Manual 3-8 www.natinst.com

Chapter 3 Theory of Operation

Input Channel 0

+ –

LPF

To Output

–

Stage

+ –

EX0

Input Channel 1

+ –

LPF

+ –

EX1

LPF

To Output

–

Stage

Input Channel 2

+ –

LPF

+ –

EX2

LPF

To Output

–

Stage

Input Channel 3

+ –

LPF

To Output

–

Stage

+ –

EX3

MTEMP

DTEMP

Figure 3-5. Analog Input Block Diagram

Chapter 3 Theory of Operation

The analog input consists of four isolated single-ended noninverting amplifiers. In addition, lowpass filtering is available at the inputs. You can jumper select one of two bandwidths, 10 kHz or 4 Hz. The amplifier gain is divided into two stages, a first stage providing gains of 1, 10, 50, and 100, and a second stage providing gains of 1, 2, 5, 10, and 20. Also, the module has an internal completion network that can be used with half-bridge or quarter-bridge networks. Each channel is configurable to a diff erent bandwidth, gain, or completion network operation.

Use the following formula to determine the overall gain of a gi ven amplifier input channel:

where G

is the overall gain and G

total

×=

1stG2nd

and G

1st

are the first and

2nd

second-stage gains. It is important to note that the choice of gain in each stage will affect the amplifier ba ndwidth. To determine the bandwidth of a given gain stage use the following formula:

GBWP

-----------------=

where BW is a given amplifier stage bandwidth, GBWP is the gain bandwidth product (typically 800 kHz), and G is the gain at this stage. This BW might be of concern at high first-stage gains such as 50 and 100. In this case the first-stage amplifier has a BW equal to 16 kHz and 8 kHz, respectively. Because of this decrease in the amplifier bandwidth, the channel overall bandwidth decreases, but noise immunity improv es. If this bandwidth limitation is unacceptable, you should spread the gains over both stages, thus increasing the BW of each amplifier stage. In most cases this will introduce a negligible effect on the channel bandwidth. For example, to achiev e a gain of 100, use G 1,000 use G

= 50 and G

1st

2nd

= 20.

All the amplifier input channels are overvoltage-protected to 240 V

= 10 and G

1st

= 10 for a gain of

2nd

rms

with

power on or off. The isolated amplifiers fulfill two purposes on the SCXI-1121 module.

They convert a small signal riding on a high common-mode voltage into a single-ended signal with respect to the SCXI-1121 chassis ground. With this conversion, the input analog signal can be extracted from a high common-mode voltage or noise before being sampled and conv erted by the data acquisition board. The isolated amplifier also amplifies and conditions an input signal, which results in an increase in measurement resolution and accuracy .

SCXI-1121 User Manual 3-10 www.natinst.com

After isolation, further filtering is available to increase the noise immunity of the amplifier channel. It is important to note that the overall amplifier bandwidth is determined by both filtering stages, so to achieve the required bandwidth, both filtering sections should be set the same, as indicated in Chapter 2, Configuration and Installation.

Excitation Output Channels

In addition to the four input channels, the SCXI-1121 contains four fully isolated excitation channels, each corresponding to an input channel. For instance, input channel 0 corresponds to excitation channel 0. Each excitation channel consists of a voltage/current source with overvoltage protection and current limiting. Two levels of excitation are available for each mode of operation. In the voltage mode you can set the level to

3.333V or 10 V in the current mode you can set the level to 150 µA or 450µA. You can choose one configuration out of the four available. To configure the excitation channels refer to Chapter 2, Configuration and

Installation. The excitation channels are isolated from each other and are

independently configurable for voltage or current excitation.

Calibration

Chapter 3 Theory of Operation

Calibration Equipment Requirements

For best measurement results, calibrate the SCXI-1121 so that its offset is adjusted to 0 ± 3 mV RTO and 0 ± 6 µV RTI and its excitation output is adjusted to ±0.04%. According to standard practice, the equipment used to calibrate the SCXI-1121 should be 10 times as accurate as the SCXI-1121, that is, have 0.004% rated accuracy. Practically speaking, calibration equipment with four times the accuracy of the item under calibration is generally considered acceptable. Four times the SCXI-1121 accuracy is

0.016%. To calibrate the SCXI-1121 you need the following equipment:

• For the excitation channels, you need a voltmeter with the following specifications:

– Accuracy:±0.004% standard

±0.016% sufficient – Range: 0 to +5 V for 3.333 V and greater than +10 V for 10 V – Resolution:5 1/2 digits

Chapter 3 Theory of Operation

• You also need a 120 Ω 1/4 W precision resistor with tempco less than

or equal to 5 ppm, or an ammeter with the following specifications: – Accuracy: ±0.004% standard

±0.016% sufficient – Range: 0.5 mA – Resolution: 6 1/2 digits

• I f you use the resistor to calibrate the current e xcitation, you also need an ohmmeter with four-wire measurement and the following specifications:

– Accuracy: ±0.004% standard

±0.016% sufficient

– Range: 200 Ω – Resolution: 5 1/2 digits

A multiranging 5 1/2-digit digital multimeter can provide you with most of the necessary functions described previously. We will refer to the measuring instrument as a digital multimeter (DMM).

Each channel on the SCXI-1121 has two potentiometers dedicated for calibration. For the amplifier channels, one potentiometer is used to null the output offset; the other is used to null the input offset. On the excitation channels, one potentiometer is used to adjust the voltage reference, while the other is used to adjust the current source.

Offset Null Adjust

Follow these steps to null the offset of the amplifier channels:

1. Short the inputs of the DMM together and then connect them to chassis ground.

2. Record the measurement indicated by the DMM display. This is the DMM inherent offset and should be subtracted from subsequent measurements.

3. Short the channel inputs of interest together and then to chassis ground.

4. Set the amplifier gain to 1.

5. Connect the amplifier output to the DMM. Make sure that the DMM can achieve the accuracy and resolution you need.

6. Adjust the output potentiometer of the channel of interest until the output is 0 ± 3 mV.

7. Set the amplifier gain to 1,000.

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Chapter 3 Theory of Operation

8. Adjust the input potentiometer of the channel of interest until the output is 0 ± 6 mV.

9. Go to the next channel.

T o av oid erroneous results when nulling the amplifier, follow these steps in the order indicated.

Excitation Adjust

When calibrating the excitation channels, you should always start with the voltage excitation and then proceed to the current excitation, because the voltage excitation reference is used as a voltage reference for the current excitation. The following procedure will show you how to recalibrate your module excitation channel to the factory-calibration setting.

1. Connect a 120 Ω precision resistor to the output of your excitation channel. Before connecting this resistor, measure it with a four-wire ohmmeter and record the exact value you have measured.

2. Set up the excitation channel of interest to 3.333 V excitation level.

3. Connect your DMM leads to the excitation output as close as possible to the resistor body.

4. Adjust the excitation voltage potentiometer until you read

3.333 V ± 0.04%.

5. Set up your channel for 150 µA excitation level.

6. Adjust the excitation current potentiometer until you read (150 µA x R120) V ± 0.04%, where R precision resistor.

7. Go to the next channel.

is the measured value of the

120

If you are using an ammeter to calibrate the current excitation level, you do not need a low-tempco resistor a simple 120 Ω, 1%, 1/4 W, 100 ppm, metal-film resistor will do, and you do not need to measure the resistor. After following the previous procedure through step 4, follow these steps:

1. Remove the resistor from the excitation channel.

2. Set up your channel for 150 µA excitation level.

3. Connect the ammeter leads to the excitation channel output.

4. Adjust the excitation current potentiometer until you read 150 µA ± 0.04%.

5. Go to the next channel.

Chapter 3 Theory of Operation

Table 3-2. Calibration Potentiometer Reference Designators

This procedure calibrates the 10 V and 450 µA levels at the same time but the accuracy achieved is limited to ±0.2%. To achieve better accuracies at these levels, follow the procedure indicated above but set the excitation levels to 10 V and to 450 µA instead of 3.333 V and 150 µA. If you do so, the lower excitation levels of this channel will then be calibrated to ±0.2% instead of to 0.04%. In the factory, the module is calibrated for 3.333 V and 150 µA.

You can seal the potentiometers after calibration with antisabotage lacquer to avoid tampering with the calibration.

Table 3-2 lists the potentiometer reference designators that correspond to each channel.

Input Channel

Number

Amplifier Channel Excitation Channel

Input Null Output Null Voltage Mode Current Mode

0 R2 R3 R10 R7 1 R16 R4 R20 R17 2 R26 R5 R30 R27 3 R36 R6 R40 R37

The resistor used to calibrate the current level must be a precision type with a tempco of 5 ppm or less. Y ou should measure and record the resistor value before each calibration procedure. The DMM you are using should provide you with the required resolution and accuracy to achieve the calibration levels indicated in the paragraphs above. Annual or semi-annual calibration is recommended to maintain the accuracy level.

SCXI-1121 User Manual 3-14 www.natinst.com

Analog Output Circuitry

Figure 3-6 shows the SCXI-1121 analog output circuitry.

Chapter 3 Theory of Operation

SCXIbus

Channel 0 Channel 1 Channel 2 Channel 3

MTEMP

Output Stage and

Hardware Scan Control

Analog

Reference

Output

Mux

AB0

Switch

Channel 1

From

Channel 2

From

Channel 3

DTEMP

Figure 3-6.

Output

Stage

Control

Buffer

MCH1+From

MCH2+

MCH3+

MCH0+

MCH0–

MCH1–

MCH2–

MCH3–

MCH4+

MCH4–

Analog Output Circuitry

Rear Signal Connector

The SCXI-1121 output circuitry consists of a buffered-output multiplexer and channel-select hardware. The channel-select hardware consists of a two-bit counter, MUXCOUNTER. This counter is needed when the board is operating in the Multiplexed-Output Mode. The counter output is sent to the multiplexer address pins to determine which of the four channels is to be connected to MCH0. In the Single-Channel Read mode, the MUXCOUNTER is loaded with the desired channel number. In the Scanning mode, the counter is loaded with the first channel to be read. During the scan, the counter is clocked by SCANCLK from the data acquisition board, or TRIG0 from the SCXIbus, depending on the state of the CLKSELECT bit in the Configuration Register. During scanning operations, the MUXCOUNTER is reloaded with the channel value stored

Chapter 3 Theory of Operation

in the Configuration Register when SCANCON is high (inacti ve) and will count upwards on each rising clock edge when SCANCON is low (acti ve). In the Parallel-Output Mode, the MUXCOUNTER is disabled and its output indicates binary 00 hence, amplifier channel 0 is selected at the output multiplexer and is connected to MCH0. The three other channels are hardwired to MCH1 through MCH3 on the rear signal connector.

The output multiplexer multiplexes all four amplifier outputs and the temperature sensor reading provided on the MTEMP line. To read the temperature sensor when it is multiplexed with the other input channels, set the RTEMP bit of the Configuration Register high. This measurement is only software controlled. For hardware control of the temperature sensor reading, connect the temperature sensor to MCH4+. Notice that MCH4–, the DTS reference, is hardwired to the chassis ground. The multiplexer output connects to the MCH0± and is connected to the data acquisition board analog channel input. In the case of the MIO data acquisition boards, MCH0± on the rear signal connector corresponds to ACH0 and ACH8.

Furthermore, you can bus the multiplexed output of the SCXI-1121 via switches to AB0± on the SCXIbus and on to other modules. When you use multiple modules, you can bus the output of the module via AB0 to the module that is connected to the data acquisition board. In this case, the AB0 switches of all the modules are closed, whereas the output multiplexer of all the modules but the one being read are disabled. Refer to Chapters 2 and 5 for further details on how to configure and program multiple modules.

In addition to the Multiplexed-Output mode described in the previous paragraph, you can operate the SCXI-1121 in Parallel-Output mode. In this mode, you need no software—other than software used with your data acquisition board—to control the scanning of the four channels or to perform a single read. To access the temperature sensor in this mode, configure the temperature sensor in the DTS mode. At power up or at reset, amplifier channel 0 is selected on the output multiplexer, and hence connects to MCH0. The other four channels (three amplifier channels and one temperature channel) are hardwired to the rear signal connector . Notice that even when you select the Multiplexed-Output mode, the SCXI-1121 drives the rear signal connector pins 5 through 12. The SCXI-1121 outputs on the rear signal connector are short-circuit protected.

Refer to the following Scanning Modes section for further details on how to scan the SCXI-1121 channels.

SCXI-1121 User Manual 3-16 www.natinst.com

Scanning Modes

There are four basic types of scanning modes possible with the SCXI-1121—single-module parallel scanning, single-module multiplexed scanning, multiple-module multiplexed scanning, and multiple-chassis scanning (possible only with the SCXI-1001 chassis). For additional information, consult Chapter 2, Configuration and Installation, Chapter 5,

Programming, your data acquisition board manual, and your SCXI chassis

user manual. If you need further information, contact National Instruments.

Single-Module Parallel Scanning

Single-Module parallel scanning is the simplest scanning mode. Directly cable the SCXI-1121 to the data acquisition board as shown in Figure 3-7. In this configuration, each analog signal has its own channel. Timing signals are not necessary for this type of scanning because the module provides all channels to the data acquisition board at all times. You can implement single-module parallel scanning with any data acquisition board that is appropriately cabled to the SCXI-1121.

Chapter 3 Theory of Operation

Data Acquisition BoardSCXI-1121

Cable Assembly

Four Isolated

Floating

Single-Ended

Inputs

CH0 CH1 CH2 CH3

MCH0 MCH1 MCH2 MCH3

Figure 3-7.

Analog Input 0 Analog Input 1 Analog Input 2 Analog Input 3

Single-Module Parallel Scanning

Multiplexed Scanning

Only the MIO-16 data acquisition boards support multiplexed scanning on the SCXI-1121. During multiplexed scanning, a module sends the SCANCLK signal to Slot 0 over the TRIG0 backplane line, and Slot 0 sends unique SCANCON signals to each module. Each module uses its signal to reload MUXCOUNTER and to determine when the SCXI-1121 output is enabled. Slot 0 contains a module list first-in-first-out (FIFO) memory chip, similar to the Channel/Gain FIFO on an MIO-16 board, except that instead of having a channel number and gain setting for each entry, the Slot 0 FIFO contains a slot number and a sample count for each

Chapter 3 Theory of Operation

SCXI-1000 or SCXI-1001 Chassis

entry. The list in Slot 0 will determine which module is being accessed and for how many samples. It is important that you make sure that the lists on the data acquisition board and Slot 0 are compatible so that the samples are acquired as intended. See your SCXI chassis manual for more information.

Single-Module Multiplexed Scanning

Single-Module Multiplexed Scanning (Direct)

This is the simplest multiplexed scanning mode. Directly cable the SCXI-1121 to the data acquisition board as shown in Figure 3-8. The module sends SCANCLK onto TRIG0, and Slot 0 sends SCANCON back to the module. SCANCON will be low at all times during the scan except during changes from one Slot 0 scan list entry to the next, when SCANCON pulses high to make the MUXCOUNTER reload its starting channel. Notice that although you are using only a single module, you can put many entries with different counts in the Slot 0 FIFO, so that some channels are read more often than others. You cannot change the start channel in the module Configuration Register during a scan.

SLOT 0

SCANCON X

TRIG0

Four Isolated

Floating

Single-Ended

Inputs

SLOT X

SCXI-1121

Figure 3-8.

Data Acquisition Board

Cable

SCANCLK

MCH0

Single-Module Multiplexed Scanning (Direct)

Assembly

Timing Output

Analog Input

Single-Module Multiplexed Scanning (Indirect)

In this mode, the SCXI-1121 is not directly cabled to the data acquisition board. Instead, you connect another module to the data acquisition board, and the analog output of the SCXI-1121 is sent over Analog Bus 0, through the intermediate module, and then to the data acquisition board. The SCXI-1121 receives its MUXCOUNTER clock from TRIG0, which is sent by the intermediate module, as illustrated in Figure 3-9. Slot 0 operation is the same for direct connection scanning.

SCXI-1121 User Manual 3-18 www.natinst.com

SCANCON X

SLOT 0

Chapter 3 Theory of Operation

SCXI-1000 or SCXI-1001 Chassis

TRIG0

Data Acquisition Board

Cable

Assembly

Timing Output Analog Input

SCXI-1121

SLOT X

SCANCLK

MCH0

Other

Module

Analog Bus 0

Figure 3-9. Single-Module Multiplexed Scanning (Indirect)

Multiple-Module Multiplexed Scanning

In this mode, all the modules tie into Analog Bus 0, and SCANCON enables the output of their amplifiers. The module that is directly cabled to the data acquisition board sends SCANCLK onto TRIG0 for the other modules and Slot 0, as illustrated in Figure 3-10. The scan list in Slot 0 is programmed with the sequence of modules and the number of samples per entry.

SCXI-1000 or SCXI-1001 Chassis

SCANCON X

Data Acquisition Board

Timing

Output

Analog

Input

Cable Assembly

SCANCON A

SLOT 0

SCANCON B

SLOT A

TRIG0

SCXI Module

SLOT B

SCXI ModuleSCXI Module

Analog Bus 0

SLOT X

SCANCLK

MCH0

Figure 3-10. Multiple-Module Multiplexed Scanning

Chapter 3 Theory of Operation

Multiple-Chassis Scanning

In this mode, you attach each SCXI-1001 chassis to a daisy chain of cable assemblies and multichassis adapter boards, as illustrated in Figure 3-11. You program each chassis separately, and each chassis occupies a dedicated channel of the data acquisition board. Within each chassis, scanning operations act as if the other chassis are not being used, with one exception. You must program the Slot 0 scan list in each chassis with dummy entries of Slot 13 to fill the samples when the data acquisition board will be sampling another chassis or data acquisition board channel. This will keep the chassis synchronized. Notice that you can only perform multiple-chassis scanning with the SCXI-1001 chassis and MIO-16 data acquisition boards. See Chapter 5, Programming, for more information on multiple-chassis scanning. See Appendix E, SCXI-1121 Cabling, for more information on the necessary cable accessories for multichassis scanning.

Data Acquisition Board

Input Ch. N

Input Ch. 1 Input Ch. 0

Timing Output

Cable

Assembly

Multichassis

Adapter

Figure 3-11.

Cable

Assembly

Multichassis

Adapter

Cable

Assemblies

Chassis 2Chassis 1

Chassis

Multiple-Chassis Scanning

Multichassis

Adapter

Chassis N

SCXI-1121 User Manual 3-20 www.natinst.com

This chapter describes in detail the SCXI-1121 Module ID Register, the Configuration Register, the Slot 0 registers, and multiplexer addressing.

Note

If you plan to use a programming software package such as NI-DAQ, LabWindows,

or LabVIEW with your SCXI-1121 board, you do not need to read this chapter.

Register Description

Register Description Format

The register description chapter discusses each of the SCXI-1121 registers and the Slot 0 registers. A detailed bit description of each register is given. The individual register description gives the type, word size, and bit map of the register, followed by a description of each bit.

The register bit map shows a diagram of the register with the MSB shown on the left (bit 15 for a 16-bit register, bit 7 for an 8-bit register), and the LSB shown on the right (bit 0). A rectangle is used to represent each bit. Each bit is labeled with a name inside its rectangle. An asterisk (*) after the bit name indicates that the bit is inverted (negative logic). The Module ID register has a unique format described in the Module ID Register section.

In many of the registers, several bits are labeled with an X, indicating don’t care bits. When you write to a register you may set or clear these bits without effect.

SCXI-1121 Registers

The SCXI-1121 has two registers. The Module ID Register is a four-byte, read-only register that contains the Module ID number of the SCXI-1121. The Configuration Register is a 16-bit, write-only register that controls the functions and characteristics of the SCXI-1121.

Chapter 4 Register Descriptions

Module ID Register

The Module ID Register contains the 4-byte module ID code for the SCXI-1121. This code number will be read as the first four b ytes on the MISO line whenev er the module is accessed. The bytes will appear least significant byte first. Within each byte, data is sent out most significant bit first. Additional data transfers will result in all zeros being sent on the MISO line. The Module ID Register is reinitialized to its original value each time the SCXI-1121 is deselected by the SS* signal on the backplane.

Type: Read-only Word Size: 4-byte Bit Map: Byte 0

76543210 00000010

Byte 1

76543210 00000000

Byte 2

76543210 00000000

Byte 3

76543210 00000000

SCXI-1121 User Manual 4-2 www.natinst.com

Chapter 4 Register Descriptions

Configuration Register

The Configuration Register contains 16 bits that control the functions of the SCXI-1121. When SS* is asserted (low) and D*/A indicates data (low), the register will shift in the data present on the MOSI line, bit 15 first, and then latch it when the SCXI-1121 is deselected by the SS* signal on the backplane. The Configuration Register initializes to all zeros when the SCXI chassis is reset or first turned on.

Type: Write-only Word Size: 16-bit Bit Map:

15 14 13 12 11 10 9 8

CLKOUTEN CLKSELECT SCAL X X X CHAN1 CHAN0

76 5 4 3 2 1 0

X X RTEMP RSVD SCANCLKEN SCANCONEN AB0EN FOUTEN*

Bit Name Description

15 CLKOUTEN Scanclock Output Enable—This bit determines whether

the SCANCLK signal from the rear signal connector is sent out, in inverted form, to the TRIG0 backplane signal. If CLKOUTEN is set to 1, SCANCLK* is transmitted on TRIG0. If CLKOUTEN is cleared to 0, SCANCLK* is not transmitted on TRIG0.

14 CLKSELECT Scanclock Select—This bit determines whether the

SCXI-1121 uses SCANCLK or the inverted form of TRIG0 to clock the MUXCOUNTER for the purpose of scanning through the analog channels. If CLKSELECT is cleared to 0, SCANCLK is used to clock MUXCOUNTER. If CLKSELECT is set to 1, TRIG0* is used as the source to clock MUXCOUNTER.

13 SCAL Shunt Calibrate—This bit determines whether the shunt

calibration switches on the SCXI-1321 are closed or open. If SCAL is cleared to 0, the switches are open. If SCAL is set to 1, the shunt calibration switches on the SCXI-1321 are closed and an R

is placed in parallel with the

SCAL

bridge between EX+ and CH+ on all four channels.

12-10, 7-6 X Don’t care bits.

Chapter 4 Register Descriptions

9-8 CHAN<1..0> Channel Select—These bits determine the channel number

5 RTEMP Read Temperature—This bit determines whether the

4 RSVD Reserved—This bit should always be written to zero. 3 SCANCLKEN Scan Clock Enable—This bit determines whether

(zero to three) that is loaded into the MUXCOUNTER to determine the analog channel to be read during a single read, or the starting channel on the module for a scanned data acquisition. CHAN1 is the MSB.

selected channel output or the MTEMP signal is driven onto the MCH0± pins of the rear signal connector. If RTEMP is cleared to zero, the selected channel output is used as the module output. If RTEMP is set to one, the MTEMP signal is used as the module output. The module output will only be driven when FOUTEN* is cleared to 0, or SCANCON is active (low) while SCANCONEN* is cleared.

MUXCOUNTER will increment on each clock signal (the clock source is determined by CLKSELECT), or keep its loaded value. If SCANCLKEN is set to one, MUXCOUNTER will be clocked during scans. If SCANCLKEN is cleared to zero, MUXCOUNTER will not be clocked.

2 SCANCONEN Scan Control Enable—This bit, whe n high, enables the

SCANCON signal.

1 AB0EN Analog Bus 0 Enable—This bit determines whether

Analog Bus 0 on the SCXIbus drives MCH0 on the rear signal connector. If AB0EN is cleared to zero, Analog Bus 0 does not drive MCH0. If AB0EN is set to one, Analog Bus 0 + drives MCH0+ through a buffer and a Analog Bus 0 – is connected to MCH0–.

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0 FOUTEN* Forced Output Enable—This bit determines whether the

Slot 0 Register Descriptions

Slot 0 has three registers. The Slot-Select Register is a 16-bit, write-only register that determines with which slot the data acquisition board will speak when SLOT0SEL* is released high. In the case of the SCXI-1001 chassis, the Slot-Select Register also determines in which chassis the desired slot is. The FIFO Register is a 16-bit, write-only register used for storing the Slot 0 scan list that determines the chassis scan sequence. The Hardscan Control Register (HSCR) is an 8-bit, write-only register used for setting up the timing circuitry in Slot 0. The Slot-Select Register is written to by using the SLOT0SEL* line. The HSCR and the FIFO Register are written to as if they were registers located on modules in Slots 13 and 14. It is recommended that you maintain software copies of the Slot-Select Register, HSCRs, and all the Slot 0 scan lists that correspond to the writes to FIFO Registers.

Chapter 4 Register Descriptions

module will drive the MCH0± pins on the rear signal connector with either the selected channel output or the MTEMP signal, depending on the state of RTEMP. If FOUTEN* is cleared to zero, the MCH0± pins will be driven through a buffer by the selected channel output or the MTEMP line. If FOUTEN* is set to one, the MCH0± pins will not be driven by the selected channel output or MTEMP, unless SCANCON is active (low) and the SCANCONEN bit is cleared. If the selected channel output or MTEMP is driving the output buffer, it will d rive Analog Bus 0 if AB0EN is set. If nothing is driving the output buffer, the SCXI-1121 output will saturate.

If you are using multiple chassis, it is important to understand the architectural differences of the Slot-Select Register as compared to the HSCR and the FIFO Register. Although each chassis has its own physical Slot-Select Register, all are written to at the same time. The jumper settings in Slot 0 of a chassis determine with which chassis number Slot 0 is identified. From the software perspective, only one Slot-Select Register exists in a system composed of multiple chassis. The HSCR and FIFO Register, on the other hand, are unique to each chassis and you must program them separately.

Chapter 4 Register Descriptions

Slot-Select Register

The Slot-Select Register contains 16 bits that determine which module in which chassis will be enabled for communication when the SLOT0SEL* line is set to one. An SCXI-1000 chassis will select the appropriate module in its chassis, regardless of the chassis number written. The Slot-Select Register will shift in the data present on the MOSI line, bit 16 first, when SLOT0SEL* is cleared to zero.

Type: Write-only Word Size: 16-b it Bit Map:

15 14 13 12 11 10 9 8

XXXXXXXCHS4

76543210

CHS3 CHS2 CHS1 CHS0 SL3 SL2 SL1 SL0

Bit Name Description

15-9 X Don’t care bits. 8-4 CHS<4..0> Chassis Bit 4 through 0—These bits determine which

chassis is selected. On the SCXI-1000 chassis, these bits are don’t cares.

3-0 SL<3..0> Slot Bit 3 through 0—These bits determine which slot in

the selected chassis is selected.

SCXI-1121 User Manual 4-6 www.natinst.com

Chapter 4 Register Descriptions

Hardscan Control Register (HSCR)

The HSCR contains eight bits that control the setup and operation of the hardscan timing circuitry of Slot 0. To write to the HSCR, follow the procedure given in the Register Writes section of Chapter 5, Programming, using 13 as the slot number, and writing eight bits to the HSCR. The register will shift in the data present on the MOSI line, bit seven first, when Slot 13 is selected by the Slot-Select Register.

Type: Write-only Word Size: 8-bit Bit Map:

765432 1 0

RSVD FRT RD ONCE HSRS* LOAD* SCANCONEN CLKEN

Bit Name Description

7 RSVD Reserved. 6 FRT Forced Retransmit—This bit, when clear, causes the scan

list in the FIFO to be reinitialized to the first entry, thus allowing the scan list to be reprogrammed in two steps instead of having to rewrite the entire list. When this bit is set, it has no effect.

5 RD Read—This bit, when clear, prevents the FIFO from being

read. When set, the FIFO is being read except at the end of a scan list entry during scanning, when reading is briefly disabled to advance to the next scan list entry.

4 ONCE Once—When set, this bit will cause the Hardscan circuitry

to shut down at the end of the scan list circuitry during a data acquisition. When clear, the circuitry will wrap around and continue with the first scan list entry after the entry is finished.

3 HSRS* Hardscan Reset—When clear, this bit causes all the

hardware scanning circuitry, including the FIFO, to be reset to the power up state. When set, this bit has no effect.

2 LOAD* Load—T his bit, when clear, forces a loading of the Slot 0

sample counter with the output of the FIFO. When set, this bit has no effect.

Chapter 4 Register Descriptions

1 SCANCONEN Scan Control Enable—When set, this bit enable s the

0 CLKEN Clock Enable—When set, this bit enables TRIG0 as a

SCANCON lines. When clear, all SCANCON lines are disabled (high).

clock for the hardscan circuitry. When clear, TRIG0 is disabled.

SCXI-1121 User Manual 4-8 www.natinst.com

Chapter 4 Register Descriptions

FIFO Register

The FIFO Register is used to add entries to the Slot 0 FIFO. The FIFO contains the Slot 0 scan list. Each entry contains a slot number to be accessed, and a count number to determine the number of samples to be taken from that slot. To write to the FIFO Register, follow the procedure given in the Register Writes section of Chapter 5, Programming, using 14 as the slot number, and writing 16 bits to the FIFO Register . The register will shift in the data present on the MOSI line, bit 15 first, when Slot 14 is selected by the Slot-Select Register. The Slot 0 scan list is created by consecutive writes to the FIFO Register. Each write creates a new entry at the end of the scan list. The maximum number of entries is 256. To clear the FIFO of all entries, clear the HSRS* bit in the HSCR.

Type: Write-only Word Size: 16-b it Bit Map:

15 14 13 12 11 10 9 8

X X X X X MOD3 MOD2 MOD1

76543210

MOD0 CNT6 CNT5 CNT4 CNT3 CNT2 CNT1 CNT0

Bit Name Description

15-11 X Don’t care bits—Unused. 10-7 MOD<3..0>Module Number—The value of these bits plus

on determines the number of the slot to be accessed fo r this scan entry. For example, to access Slot 6, MOD<3..0> would be 0101.

6-0 CNT<6..0> Count—The value of th ese bits plus one determines ho w

many samples will be taken before the next scan list entry becomes active. A value of zero corresponds to one sample and a value of 127 corresponds to 128 samples.

Programming

This chapter contains a functional programming description of the SCXI-1121 and Slot 0.

Note

If you plan to use a programming software package such as NI-DAQ, LabWindows,

or LabVIEW with your SCXI-1121 board, you do not need to read this chapter.

Programming Considerations

Programming the SCXI-1121 involves writing to the Configuration Register. Programming Slot 0 involves writing to the HSCR and FIFO Register. Programming the data acquisition boards involves writes to their registers. See your data acquisition board user manual for more information. The programming instructions list the sequence of steps to take. The instructions are language independent that is, they instruct you to write a value to a given register without presenting the actual code.

Notation

For the bit patterns to be written, the following symbols are used:

0 Binary zero 1 Binary one X Don't care, either zero or one may be written C One of two bits used to specify the channel to be loaded into the

MUXCOUNTER. This value will either be the channel to be read for single reads, or a starting channel for scanned measurements.

The 16-bit patterns are presented MSB first, left to right.

Chapter 5 Programming

Register Writes

This section describes how to write to the Configuration Register, HSCR, and FIFO Register including the procedure for writing to the Slot-Select Register to select the appropriate slot. For timing specifics, refer to the

Timing Requirements and Communication Protocol section in Chapter2,

Configuration and Installation. The rear signal connector pin equivalences

to the different National Instruments data acquisition boards are given in Table5-1. See also AppendixE, SCXI-1121 Cabling. The Configuration Register, the FIFO Register, and the HSCR are write-only registers.

The different bits in these registers often control independent pieces of circuitry. There are times when you may want to set or clear a specific bit or bits without affecting the remaining bits. However, a write to one of these registers will affect all bits simultaneously. You cannot read the registers to determine which bits have been set or cleared in the past therefore, you should maintain a software copy of these registers. You can then read the software copy to determine the status of the register. To change the state of a single bit without disturbing the remaining bits, set or clear the bit in the software copy and write the software copy to the register.

Table 5-1.

SCXI-1121

SCXIbus

Line

MOSI SERDATIN ADIO0 PB4 DOUT4 D*/A DAQD*/A ADIO1 PB5 DOUT5 INTR* SLOT0SEL* ADIO2 PB6 DOUT6 SPICLK SERCLK EXTSTROBE* PB7 DOUT7 MISO SERDATOUT BDIO0 PC1 DIN6

Rear Signal

Connector

SCXI-1121 Rear Signal Connector Pin Equivalences

MIO-16 Lab Board PC-LPM-16

Register Selection and Write Procedure

1. Select the slot of the module to be written to (or Slot 13 or 14). Initial conditions: SERDATIN = X DAQD*/A = X SLOT0SEL* = 1 SERCLK = 1

2. Clear SLOT0SEL* to 0. This will deassert all SS* lines to all modules in all chassis.

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Chapter 5 Programming

3. For each bit, starting with the MSB first (bit 15): a. SERDATIN = bit to be sent. These bits are the data that is being

written to the Slot-Select Register. b. Clear SERCLK to 0. c. Set SERCLK to 1. This rising edge clocks the data. (If you are

using an MIO-16 board, writing to the EXTSTROBE* register

will pulse EXTSTROBE* low and then high, accomplishing

steps 3b and 3c.)

4. Set SLOT0SEL* to 1. This will assert the SS* line of the module whose slot number was written to Slot 0. If you are using multiple chassis, the appropriate slot in the chassis whose address corresponds to the written chassis number will be selected automatically. When no communications are taking place between the data acquisition board and any modules, write zero to the Slot-Select Register to ensure that no accidental writes occur.

5. If you are writing to a Configuration Register, clear DAQD*/A to 0 (this indicates data will be written to the Configuration Register). If you are writing to the HSCR or FIFO Register, leave DAQD*/A high.

6. For each bit to be written to the Configuration Register: a. Establish the desired SERDATIN level corresponding to this bit. b. Clear SERCLK to 0. c. Set SERCLK to 1 (clock the data). (If you are using an MIO-16

board, writing to the EXTSTROBE* register will pulse EXTSTROBE* low and then high, accomplishing steps 6b and 6c.)

7. Pull SLOT0SEL* low to deassert the SS* line, latch the data into the Configuration Register and establish conditions for writing a new slot select number to the Slot 0 Slot-Select Register.

8. If you are not selecting another slot, write zero to the Slot 0 Slot-Select Register. If you are selecting another slot, start at step 3.

For a timing illustration of a Configuration Register write, see Figure 2-18,

Configuration Register Write Timing Diagram, which shows the proper

write to configure an SCXI-1121 that is directly cabled to an MIO-16 for multiple-module multiplexed scanning with a start channel of 3.

Initialization

The SCXI-1121 powers up with its Configuration register cleared to all zeros. You can force this state by an active low signal on the RESET* pin of the backplane connector. In the reset state, CH0 through CH3 are routed

Chapter 5 Programming

to MCH0 through MCH3 on the rear signal connector. The module is disconnected from Analog Bus 0 and disabled from scanning.

Single-Channel Measurements

This section describes how to program the SCXI-1121, either alone or in conjunction with other modules, to make single-channel, or nonscanned, measurements.

Direct Measurements

Parallel Output

In order to perform a parallel output measurement, you must cable the SCXI-1121 rear signal connector to a data acquisition board with each output connected to a different data acquisition board channel. See Chapter 2, Configuration and Installation, for more information. For information on how to make the voltage measurement with your data acquisition board, consult your data acquisition board user manual. Remember to account for the gains of both the SCXI-1121 and the data acquisition board when calculating the actual voltage present at the input of the SCXI-1121.

T o measure one of the four differential input channels to the SCXI-1121, or the DTEMP line if the module has been configured appropriately , perform the following steps:

1. Write the binary pattern Configuration Register. Notice that this can be the RESET state.

2. Measure the voltage with the data acquisition board.

000XXX00 XX000000 to the SCXI-1121

Multiplexed Output

In order to perform a direct multiplexed output measurement, you must cable the SCXI-1121 rear signal connector to a data acquisition board. See Chapter 2, Configura tion and Installation, for more information. For information on how to make the voltage measurement with your data acquisition board, consult your data acquisition board user manual. Remember to account for the gains of both the SCXI-1121 and the data acquisition board when calculating the actual voltage present at the input of the SCXI-1121.

SCXI-1121 User Manual 5-4 www.natinst.com

Chapter 5 Programming

To measure one of the four differential input channels to the SCXI-1121, perform the following steps:

1. Write the binary pattern

000XXXCC XX000000 to the SCXI-1121

Configuration Register.

2. Measure the voltage with the data acquisition board. To shunt calibrate one of the four differential input channels, perform the

following steps:

1. Write the binary pattern

001XXXCC XX00000 to the SCXI-1121

Configuration Register. Insert a delay of at least 1 sec if you have set the 4 Hz filter , or at least 1 msec if you ha v e set the 10 kHz f ilter. This delay permits the SCXI-1121 amplifier to settle.

2. Measure the voltage with the data acquisition board. To measure the voltage on the MTEMP line, perform the following steps:

1. Write the binary pattern

000XXXXX XX100000 to the SCXI-1121

Configuration Register.

2. Measure the voltage with the data acquisition board.

Indirect Measurements

Indirect measurements involve one module sending a signal to Analog Bus 0, where it is picked up by another module and transmitted to the data acquisition board.

Measurements from Other Modules

To perform measurements from other modules, you must cable the SCXI-1121 rear signal connector to a data acquisition board. See Chapter 2, Configuration and Installation, for more information. To make a measurement from another module, perform the following steps:

1. Perform any necessary programming to ensure that no modules are driving Analog Bus 0. For an SCXI-1121, clearing AB0EN in the Configuration Register will ensure that its output is not driving AB0.

2. Write the binary pattern Configuration Register . This step disables the SCXI-1121 from driving Analog Bus 0 and allows Analog Bus 0 to drive MCH0 through the output buffer.

3. Program the other module to drive Analog Bus 0 with the signal to be measured.

4. Measure the voltage with the data acquisition board.

000XXXXX XX100011 to the SCXI-1121

Chapter 5 Programming

Measurements from the SCXI-1121 via Another Module

To perform measurements via another module, you must cable the other module rear signal connector to a data acquisition board. The other module must also be able to transfer Analog Bus 0 to the data acquisition board. See Chapter 2, Configuration and Installation, for more information.

To measure one of the four differential input channels to the SCXI-1121, perform the following steps:

1. Perform any necessary programming to ensure that no modules are driving Analog Bus 0. For an SCXI-1121, clearing AB0EN in the Configuration Register will ensure that its output is not driving AB0.

2. Program the other module not to drive Analog Bus 0, but to send Analog Bus 0 to the data acquisition board.

3. Write the binary pattern Configuration Register.

4. Measure the voltage with the data acquisition board.

T o perform a shunt calibration on one of the four differential input channels of the SCXI-1121, perform the following steps:

1. Perform any necessary programming to ensure that no modules are driving Analog Bus 0. For an SCXI-1121, clearing AB0EN in the Configuration Register will ensure that its output is not driving AB0.

2. Program the other module not to drive Analog Bus 0, but to send Analog Bus 0 to the data acquisition board.

3. Write the binary pattern Configuration Register.

4. Insert a delay equal to 1 sec if you have set the 4 Hz filter , or 1 msec if you have set the 10 kHz filter. This delay permits the SCXI-1121 amplifier to settle.

5. Measure the voltage with the data acquisition board.

000XXXCC XX000010 to the SCXI-1121

001XXXCC XX000010 to the SCXI-1121

To measure the voltage on the MTEMP line, perform the following steps:

1. Perform any necessary programming to ensure that no modules are driving Analog Bus 0. For an SCXI-1121, clearing AB0EN in the Configuration Register will ensure that its output is not driving AB0.

2. Program the other module not to drive Analog Bus 0, but to send Analog Bus 0 to the data acquisition board.

3. Write the binary pattern

000XXXXX XX100010 to the SCXI-1121

Configuration Register.

4. Measure the voltage with the data acquisition board.

SCXI-1121 User Manual 5-6 www.natinst.com

Scanning Measurements

Programming for scanned data acquisition involves programming your data acquisition board, modules, and Slot 0. In general, the steps to be taken are as follows:

1. Perform all data acquisition board programming to the point of enabling the data acquisition.

2. Perform all module programming.

3. Program the Slot 0 hardscan circuitry.

4. Enable the data acquisition, trigger it either through software or hardware, and service the data acquisition.

The MIO and Lab-PC+ boards can do all types of scanning. Lab-NB, Lab-PC, Lab-PC+, Lab-LC, and PC-LPM-16 boards support only single-module parallel scanning, and do not support any of the multiplexed scanning modes. Notice that single-module parallel scanning is typically done without any module or Slot 0 programming only programming the data acquisition board is necessary.

1. Data Acquisition Board Setup Programming

The programming steps for your data acquisition board are given in your data acquisition board user manual. You should follow the instructions in the following sections:

• AT-MIO-16 User Manual – Multiple A/D Conversions with Continuous Channel Scanning

– Multiple A/D Conversions with Interval Channel Scanning

• AT-MIO-16D User Manual – Multiple A/D Conversions with Continuous Channel Scanning

– Multiple A/D Conversions with Interval Channel Scanning

• AT-MIO-16F-5 User Manual – Posttrigger Data Acquisition with Continuous Channel Scanning – Posttrigger Data Acquisition with Interval Channel Scanning

Chapter 5 Programming

(Round Robin)

(Pseudosimultaneous)

(Round Robin)

(Pseudosimultaneous)

Chapter 5 Programming

• AT-MIO-16X User Manual – Continuous Channel Scanning Data Acquisition – Interval Channel Scanning Data Acquisition

• AT-MIO-64F-5 User Manual – Continuous Channel Scanning Data Acquisition – Interval Channel Scanning Data Acquisition

• Lab-LC User Manual – Programming Multiple A/D Conversions with Channel Scanning

• Lab-NB User Manual – Programming Multiple A/D Conversions with Channel Scanning

• Lab-PC User Manual – Programming Multiple A/D Conversions with Channel Scanning

• Lab-PC+ User Manual – Programming Multiple A/D Conversions with Channel Scanning – Programming Multiple A/D Conversions with Interval Scanning – Programming Multiple A/D Conversions in Single-Channel

Interval Acquisition Mode

• MC-MIO-16 User Manual – Multiple A/D Conversions with Continuous Channel Scanning

(Round Robin)

– Multiple A/D Conversions with Interval Channel Scanning

(Pseudosimultaneous)

• NB-MIO-16 User Manual – Programming Multiple A/D Conversions with Channel Scanning

• NB-MIO-16X User Manual – Multiple A/D Conversions with Continuous Channel Scanning

(Round Robin)

– Multiple A/D Conversions with Interval Channel Scanning

(Pseudosimultaneous)

• PC-LPM-16 User Manual – Programming Multiple A/D Conversions with Channel Scanning

SCXI-1121 User Manual 5-8 www.natinst.com

Chapter 5 Programming

Follow the instructions in these sections through the part labeled as follows:

• Clear the A/D Circuitry and Reset the Mux Counter in the MIO board user manual (except for the AT -MIO-16X and the AT -MIO-64F-5). Do not continue to the part called Enable the Scanning Data Acquisition Operation. You will do this after you program the modules and Slot 0.

• Program the Sample Counter (if you are doing continuous channel scanning) or Program the Scan-Interval Counter (if you are doing interval channel scanning) in the A T-MIO-16X or A T-MIO-64F-5 user manual. Do not continue to the part labeled Enable a Scanning Data

Acquisition Operation or Enable an Interval Scanning Data Acquisition Operation. Y ou will do this after you program the modules

and Slot 0.

Note For multiplexed scanning with an MIO board, it is important that you follow the

instructions in the channel-scanning sections, not the single-channel sections. Although you may be using only one MIO board channel, the channel scanning programming will ensure that the MIO board outputs SCANCLK, which is needed by the SCXI-1120 and Slot 0.

• Clear the A/D Circuitry in the Lab-LC User Manual. Do not continue to the part called Program the Sample-Interval Counter. You will do this after you program the modules and Slot 0.

• Clear the A/D Circuitry in the Lab-PC User Manual, the Lab-PC+ User Manual, and the PC-LPM-16 User Manual. Do not continue to the part called Start and Service the Data Acquisition Operation. You will do this after you program the modules and Slot 0.

• Clear the A/D Circuitry in the Lab-NB User Manual. Do not continue to the part called Program the Sample-Interval Counter (Counter A0). You will do this after you program the modules and Slot 0.

Counter 1 and SCANDIV

All MIO boards can operate their data acquisition board scan lists in two ways—they can acquire one sample per data acquisition board scan list entry or they can acquire N samples per data acquisition board scan list entry, where N is a number from 2 to 65,535 that is programmed in Counter 1. This second method of operation is especially useful when the data acquisition board scan list length is limited to 16 entries, as it is on all MIO boards except the AT-MIO-16F-5, which can have up to 512 entries. Because you can multiplex many SCXI-1121s in one chassis to one MIO board channel, often the simplest way to program the MIO board is to use only one data acquisition board scan list entry, and make N the total number of samples to be taken on all modules in one scan. Check your MIO board user manual for limitations in the data acquisition board scan list format.

National Instruments SCXI-1121 User Manual

Specifications and Main Features

Frequently Asked Questions

User Manual

SCXI-1121 User Manual

Worldwide Technical Support and Product Information

National Instruments Corporate Headquarters

Worldwide Offices

Important Information

Warranty

Copyright

Trademarks

WARNING REGARDING USE OF NATIONAL INSTRUMENTS PRODUCTS

Contents

Figures

Tables

About This Manual

Conventions

Related Documentation

What Your Kit Should Contain

Optional Software

Optional Equipment

Custom Cables

Unpacking

Module Configuration

Figure 2-2. SCXI-1121 Detailed Parts Locator Diagram

Digital Signal Connections

Jumper W44

Jumper W38

Jumper W32

Using Jumpers W32 and W38

Table 2-1. Digital Signal Connections, Jumper Settings

Analog Configuration

Grounding, Shielding, and Reference Mode Selection

Table 2-2. Jumper W33 Settings

Input Channel Jumpers

Excitation Jumpers

Table 2-7. Maximum Load per Excitation Channel

Table 2-8. Excitation Level Jumper Selection

Hardware Installation

Signal Connections

Front Connector

Figure 2-3. SCXI-1121 Front Connector Pin Assignment

Front Connector Signal Descriptions

Analog Input Channels

Figure 2-6. Floating AC-Coupled Signal Connection

Figure 2-7. AC-Coupled Signal Connection with High Common-Mode Voltage

Excitation Channels

Temperature Sensor Connection

Connector-and-Shell Assembly

Figure 2-8. Assembling and Mounting the SCXI-1330 Connector-and-Shell Assembly

Table 2-11. Nulling Resistors and Corresponding Channel

Figure 2-9. Nulling Circuit

Table 2-12. Jumper Settings of the Nulling Circuits

Figure 2-10. Shunt Circuit

Table 2-13. Jumper Settings on the SCXI-1320 Terminal Block

Table 2-14. Jumper Settings on the SCXI-1328 Terminal Block

Table 2-15. Jumper Settings on the SCXI-1321 Terminal Block

Figure 2-11. SCXI-1320 Parts Locator Diagram

Figure 2-12. SCXI-1328 Parts Locator Diagram

Figure 2-13. SCXI-1321 Parts Locator Diagram

Rear Signal Connector

Rear Signal Connector Signal Descriptions

Analog Output Signal Connections

Digital I/O Signal Connections

Table 2-16. SCXIbus to SCXI-1121 Rear Signal Connector to Data Acquisition Board Pin Equivalences

Timing Requirements and Communication Protocol

Communication Signals

Figure 2-16. Slot-Select Timing Diagram

Figure 2-17. Serial Data Timing Diagram

Figure 2-18. Configuration Register Write Timing Diagram

Figure 2-19. SCXI-1121 Module ID Register Timing Diagram

Functional Overview

SCXIbus Connector

SCXIbus Connector Signal Descriptions

Table 3-1. SCXIbus Equivalents for the Rear Signal Connector

Digital Interface

Digital Control Circuitry

Analog and Timing Circuitry

Analog Input Channels