Tektronix DAS-800 Series Users Guide

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DAS-800 Series

User’s Guide

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DAS-800 Series

User’s Guide

Revision A - December 1993

Part Number: 85790

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The information contained in this manual is believed to be accurate and reliable. However, the manufacturer assumes no responsibility for its use; nor for any infringements or patents or other rights

of third parties that may result from its use. No license is granted by implication or otherwise under any

patent rights of the manufacturer.

THE MANUFACTURER SHALL NOT BE LIABLE FOR ANY SPECIAL, INCIDENTAL, OR CONSEQUENTIAL DAMAGES RELATED TO THE USE OF THIS PRODUCT. THIS PRODUCT

IS NOT DESIGNED WITH COMPONENTS OF A LEVEL OF RELIABILITY THAT IS SUITED

FOR USE IN LIFE SUPPORT OR CRITICAL APPLICATIONS.

All brand and product names are trademarks or registered trademarks of their respective companies,

0 Copyright Keithley Instruments, Inc., 1993.

All rights reserved. Reproduction or adaptation of any part of this documentation beyond that permitted by Section 117 of the 1976 United States Copyright Act without permission of the Copyright owner is unlawful.

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Table of Contents

Preface

1 Overview

Supporting Software . . . . . . . . . . . . .

Accessories

2 Functional Description

Analog Input Features ..............

Channel Configuration ...........

Input Configuration ...........

Gains and Ranges. ............

Channel Selection ............

Channel Expansion ...........

Conversion Clock Sources ........

Triggers. ......................

Gates .........................

Data Transfer. ..................

Digital I/O Features ................

8254 Counternimer Circuity ........

Interrupts ........................

Power ...........................

........

.......

. . . . l-2

. . . . 1-4

. ...2-2

. ...2-3

. . . .2-4

. ...2-5

. ...2-6

. ...2-8

. ..2-12 . ..2-14 . ..2-16 . ..2-17 . ..2-17 . ..2-25

. ..2-26

3 Setup and Installation

Installing the Software. ...............................

Installing the DAS-800 Series Standard Software Package . .3-5 Installing the ASO- Software Package

DOS Installation. ...............................

Windows Installation ............................

Unpacking the Board. ................................

Configuring the Board. ...............................

Creating a Configuration File.

Setting the Base Address ...........................

Setting the Input Contiguration ......................

Setting the Interrupt Level .........................

Installing the Board .................................

.3-4

.............. .3-6

.3-6 .3-7 .3-8 .3-8

....................... .3-9

.3-13 .3-16 .3-17 .3-19

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Cabling and Wiring

Attaching Accessory and Expansion Boards.

Attaching an STC-37 Screw Terminal Connector Attaching an STA-08 / STA-OSPGA Screw Terminal

Accessory. .....................................

Attaching an EXP-16 or EXP-16/A Expansion Board. Attaching an EXP-GP Expansion Board

Attaching an MB Series Backplane ...................

Connecting Multiple Expansion Boards.

Connecting Signals ..................................

Connecting an Analog Input Signal to a Single-Ended Input. 4-9 Connecting an Analog Input Signal to a Differential Input .4-10

Connecting Digital Signals, ........................

Connecting Counter/Timer I/O Signals Synchronizing Conversions on Multiple Boards

The Control Panel

..............

........ .4-3

...............

........ .4-13

.4-l

.4-4

.... .4-5

.4-6 .4-7 .4-7 .4-9

.4-12 .4-12

6 Calibration

Equipment Required Potentiometers Calibration Utility

Troubleshooting

Problem Isolation Troubleshooting Table. Technical Support

Specifications

Connector Pin Assignments

............................

.................................

..............................

...............................

..........................

..............................

c DAS-800 Series External Driver

Running the DAS-800 Series External Driver. . . . . . .

Accessing the DAS-800 Series External Driver

Special Characteristics.. . . . . . . . . . . . .

Pseudo-Digital Output: Extended Functions. . . . .

Analog Triggers

Data Formats . . . . . . . . . . . . .

Using Expansion

Board

Gains . . . .

.,6-l

.6-2 .6-4

.,7-l

. . l-2 . l-4

.c-2 .c-2 .c-3

. .c-3

.C-6 .c-9

.c-11

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Software Interrupt Vectors ......................

Counter/Iimer Functions .......................

Error Messages. .................................

Keithley Memory Manager

Installing and Setting Up the KMM.

Using

KMMSETUP.EXE

Using a Text Editor.

.......................

...........................

.................

Removing the KMM .............................

Index

List of Figures

Figure 2-l. DAS-800 Series Functional Block Diagram Figure 2-2. Channel Expansion

...................

Figure 2-3. Initiating Conversions .................

Figure 2-4. Initiating Conversions with a Hardware

Trigger

Figure 2-5. Hardware Gate.

.............................

......................

Figure 2-6. Pulse on Terminal Count Mode. .........

Figure 2-7. Programmable One-Shot Mode. .........

Figure 2-8. Rate Generator Mode.

.................

Figure 2-9. Square-Wave Generator Mode ..........

Figure 2- 10. Software-Triggered Strobe Mode ........

Figure 2-l 1 Figure 3-l. Figure 3-2. Figure 3-3. Figure 3-4. Figure 3-5. Figure 4-l. Figure 4-2.

Hardware-Triggered Strobe Mode. .......... .2-24

DAS-800 Board. ......................... .3-2

DAS-Sol/802 Board ...................... .3-3

Setting the Base Address. ................. .3-14

Setting the Input Configuration. ............ .3-17

Setting the Interrupt Level. ................ ,3-18

Main I/O Connector on a DAS-800 Board ..... .4-2

Main I/O Connector on a DAS-801 or

DAS-802 Board. ......................... .4-3

Figure 4-3.

Attaching an STC-37 Screw Terminal

Connector. .............................. .4-4

Figure 4-4.

Attaching an STA-08 / STA-OSPGA Screw

Terminal Accessory. ...................... .4-5

Figure 4-5.

Attaching an EXP-16 or EXP-16/A Expansion

Board .................................. .4-6

Figure 4-6. Figure 4-7.

Attaching an EXP-GP Expansion Board. ...... .4-7

Connecting Multiple Expansion Boards ....... .4-8

.c-12 .c-12 .c-13

. D-2

D-2

. D-3

D-4

. .2-2 . .2-l .2-10

.2-13 .2-15 ,2-19 .2-20 .2-21 .2-22 .2-23

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Figure 4-8. Figure 4-9.

Single-Ended Input , . . . . . . . . . . . . .4-10

Differential Input. . . . . . . . . . . .4-l 1

Figure 4-10. Synchronizing Conversions on Multiple

Boards . . . . . . , . . . . . . . . . . . . .4-13

Figure 4-l 1.

Figure 6-l. Figure 6-2. Figure B-l. Figure B-2. Figure C-l. Figure C-2. Figure C-3.

List of Tables

Table 2-1.

Table 2-2. Table 2-3.

Dividing the Rate of the Master Clock .4-14

Potentiometers (DAS-800) . . . . . . . . . .6-3

Potentiometers (DAS-801 / DAS-802) . .6-3

Main I/O Connector (DAS-800) . . . . .B-2

Main I/O Connector @AS-801 / DAS-802) . . .B-5 Analog Trigger Conditions . . .C-7

Using a Hysteresis Value. . , . . . . . .C-8

Initiating Conversions with an Analog Trigger. . .C-9

Supported Gains .........................

Sources for 8254 Documentation

...........

Expansion Board / Backplane Power

Limitations .............................

Table 3-1. Table 3-2. Table 3-3. Table 7-1. Table A- 1.

Default Configuration I/O Address Map (OOOH to 3FFH)

....................

..........

Interrupt Levels .........................

Troubleshooting Information.

...............

DAS-800, DAS-801, and DA.%802

Specifications. ...........................

Table B-l.

Main I/O Connector Pm Assignments for the

DAS-SOO................................B- 3

Table B-2. Table C- 1.

Table C-2. Table C-3.

Main I/O Connector Pin Assignments for the DAS-801 /DAS-802

Pseudo-Digital Output Channels

......................

.............

Interrupt Vectors ........................

Error/Status Codes

.......................

.2-4

.2-25 .2-27

.3-10 .3-14 .3-18

.7-2

A- 1

.B-6

.C-4 .C-12 .C-13

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Preface

The DAM00 Series User’s Guide provides the information needed to set up, install, and use DAS-800 Series boards.

The manual is intended for data acquisition system designers, engineers, technicians, scientists, and other users responsible for setting up, cabling,

and wiring signals to DA,%800 Series boards. It is assumed that users are familiar with application.

data

acquisition principles and with their particular

The

DAS-BOO Series

Chapter 1 provides an overview of the features of DA%800 Series boards, including a description of supported software and accessories.

Chapter 2 provides a more detailed description of the analog input, digital I/O, and counter/timer I/O features of DAS-800 Series boards.

Chapter 3 describes how to unpack, configure, and install DAS-800 Series boards.

Chapter 4 describes how to attach accessory and expansion boards and how to wire signals to DAS-800 Series boards.

Chapter 5 describes how to use the Control Panel to test the functions of DAS-800 Series boards.

Chapter 6 describes how to calibrate DAS-800 Series boards.

Chapter 7 provides troubleshooting information.

Appendix A lists the specifications for DAS-800 Series boards.

User’s Guide is organized as follows:

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. Appendix B lists the connector pin assignments. . Appendix C describes how to use the DAS-800 Series External

Driver. The DAS-800 Series External Driver allows you to use DAS-800 Series boards with certain data acquisition and analysis software packages.

. Appendix D describes the Keithley Memory Manager. The Keithley

Memory Manager allows you to allocate sufficient memory when running under Windowsm.

An index completes this manual. Throughout the manual, keep the following in mind: . References to DAS-800 Series boards apply to the DAS-800,

DAS-801, and DAS-802 boards. When a feature applies to a particular board, that board’s name is used.

. References to Microsoft@ QuickBasic” apply to both Microsoft

QuickBASIC (Version 4.0) and Microsoft QuickBasic (Version 4.5).

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Overview

The DAS-800 Series is a family of analog input and digital input and output (I/O) boards for an IBM@ PC/XTTM, AT’ or compatible computer. The DAS-80 Series includes the DAS-800, DAS-801, and DAS-802 boards, The major features of DAS-800 Series boards are as follows:

Eight analog input channels (single-ended on the DAS-800;

single-ended or differential on the DAS-801 and DAS-802).

Fixed f5 V analog input range for the DAS-800; nine unipolar and bipolar, software-selectable analog input ranges for the DAS-801 and

DAS-802. On-board 8254 counter/timer circuitry, which you can use as a

hardware internal clock source and/or for general-purpose counter/timer I/O operations.

Software-selectable conversion clock source. Digital trigger. Hardware gate.

Four-word FIFO to store converted data: overrun detection logic to detect lost dam points.

Software-selectable interrupt source. Three bits of digital input.

. Four bits of digital output.

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Note:

DAS-800 boards are enhancements of DAS-8 boards; DAS-801 boards are enhancements of DAS-8 PGA boards; DAS-802 boards are enhancements of DAS-8 PGA/G2 boards. You can use application programs written to support the DAS-8 with the DAS-800, application programs written to support the DAS-8 PGA with the DAS-801, and application programs written to support the DAS-8 PGA/GZ with the DAS-802.

Supporting Software

You can use DAS-800 Series boards with the following software:

DASJOO Series standard software package

DAS-800 Series boards. Includes function libraries for writing

application programs under DOS in a high-level Microsoft QuickBasic and Microsoft Visual BasicTM for DOS, support files, utility programs, and language-specific example programs. Refer to more information.

the DAM00 Series Function Call Driver User’s Guide

- Shipped with

language

such as

for

l-2

ASO-

software package - The optional Advanced Software

Option for DAS-800 Series boards. Includes function libraries for writing application programs under Windows and DOS in a high-level language such as Borland@ C/C++, Borland Turbo Pascal@

for DOS and Windows, and Microsoft Visual Basic for Windows; support files; utility programs; and language-specific example programs. Refer to the

Guide

for more information.

DA&800 Series utilities

DA&BOO Series Function Cull Driver User’s

- The following utilities are provided as part

of both the DAS-800 Series standard software package and the

ASO- software package:

Confgurarion urilify

-The configuration utility (D800CFG.EXE) allows you to create or modify a configuration tile. The configuration tile indicates the settings of switches and jumpers on the board and provides other configuration information. This information is used by the DAS-800 Series Function Call Driver and other software packages to perform the board’s I/O

Overview

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operations. Refer to page 3-9 for more information about the configuration utility.

Control Panel

-The Control Panel allows you to perform operations on DAS-800 Series boards, without programming. It provides a quick way to test your board and monitor

your I/O

operation. Two versions of the Control Panel are available:

CTL800.EXE (for DOS) and CTLBOOW.EXE (for Windows).

Refer to Chapter 5 for more information about the Control Panel.

Calibrafion uriliry

- The calibration utility (CALSOO.EXE) allows you to calibrate the analog input circuitry of DAS-800 Series boards. Refer to Chapter 6 for more information about the calibration utility.

. DAM300 Series custom controls

programs in Visual Basic for Windows. Refer to the Custom

. Data acquisition and analysis application software -

Controls User’s Guide

- Help you to write application

VisualDAS

for more information.

Many menu-driven, integrated software packages are available for DAS-800 Series boards, including VIEWDAC?, EASYEST LXa’, and EASYEST AGW. In addition, programming tools, such as the ASYST@ scientific and engineering programming

language, are

available to help you customize your own application program.

Note:

If you use VIBWDAC!, EASYEST LX / AG, or ASYST to

program your DAS-800 Series board, you must use the DA&800

Series External Driver, which is shipped as part of the DAS-800 Series standard software package. Refer to Appendix C for information on using the DAS-800 Series External Driver.

. DAS-800 Series register I/O map - If you cannot satisfy your

application’s requirements with the available software packages and you are an experienced programmer, you may be able to program

your DAS-800 Series

board

through direct register I/O instructions.

Contact the factory for more information.

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Accessories

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The following accessories are available for use with DAS-800 Series boards:

. STC-37 screw terminal connector - For

all DAS-800 Series boards, provides 37 screw terminals that allow you to access the functions of the board; connects directly to the DAS-800 Series board without a cable.

STA-08 screw terminal accessory - For the DAS-800 board

provides screw terminals that allow you to access the functions of the board; provides a breadboard area with power and additional screw terminals to access the user-designed circuitry.

. STA-08PGA screw terminal accessory

- For the DAS-801 and DAS-802 boards only, provides screw terminals that allow you to access the functions of the

board;

provides a breadboard area with

power and additional screw terminals to access the user-designed circuitry.

. EXP-16 and EXP-16/A expansion boards

- Sixteen-channel

multiplexer and signal-conditioning expansion boards; provide cold

junction compensation (CJC) for thermocouples and

switch-selectable gains ranging from 0.5 to 2000.

. EXP-GP expansion board

- An 8-channel signal-conditioning

expansion board; connects to RTDs, thermistors, strain gages, and

other variable resistance sensors; provides CJC for thermocouples and switch-selectable gains of 1, 10, 100, and 1000 or 2.5.25.250, and 2500.

only,

1-4

. MB Series modules and backplanes

- MB Series modules are high-performance, signal-conditioning modules that measure thermocouple, RTD, strain gage, voltage, and current inputs and are installed in MB Series backplanes. MB Series backplanes provide

screw terminals for connecting the high-level analog I/O signals.

Overview

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. STA-SCM8

screw terminal accessory - Allows you to

connect a DAS-800 Series board to up to four MB-02 backplanes; provides screw terminals that allow you to access the functions of the board; provides a breadboard area with power for the user-designed circuitry.

. C-1800 cable

-Unshielded, la-inch cable with a 37-pin connector on each end: allows you to connect a DAS-800 Series board to an STA-08, STA-08PGA, EXP-16, EXP-16/A, or EXP-GP.

. S-1800 cable - Shielded, la-inch cable with a 37-pin connector on

each end; allows you to connect a DAS-800 Series board to an STA-08, STA-OBPGA, EXP-16, EXP-16/A, or EXP-GP.

. CB-MB1

cable

- Cable with a 37-pin connector on one end and a 26-pin-connector on the other end; allows you to connect a DAS-800 Series board to an MB-01 or MB-02 backplane.

. C-2600 cable

- An la-inch cable with a26-pin connector at each end; allows you to connect an STA-SCM8 screw terminal accessory to an MB-02 backplane.

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Functional Description

This chapter describes the following features of DAS-800 Series boards: . Analog input features

. Digital I/O features . Counter/timer I/O features

Interrupts

. Power

A functional block diagram of a DAS-800 Series board is shown in

Figure 2- 1.

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Figure 2-1. DAS-800 Series Functional Block Diagram

Analog Input Features

DAS-800 Series boards use a 12-bit, successive approximation analog-to-digital converter (ADC) with integral sample and hold. The ADC provides 1Zbit resolution fl least significant bit (LSB), providing an effective accuracy of 11 bits. The ADC converts one sample every 25 ks, providing a maximum conversion frequency of 40 kHz.

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Functional Description

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Channel Configuration

DAS-800 Series boards contain eight on-board analog input channels. The following subsections describe the input configurations supported for each channel, the gains the methods of specifying a channel or channels for an analog input operation.

On the DA%801 and DAS-802, you can configure each channel as either

single-ended or differential. The differences between a single-ended and a

differential input configuration are described as follows:

and

input ranges supported for each channel, and

. Single-ended

you are measuring relatively high-level signals (greater than 1 V), if the source of the input signal is close to the board (less than two feet), or if all input signals are referred to a common ground. This configuration does not provide common-mode noise rejection.

. Differential

are measuring low-level signals, if high source resistances (greater than 100 D) exist, or if common-mode voltages exist between the voltage source and the host’s chassis ground. In a differential configuration, a separate positive and negative terminal is provided for each channel. Any common-mode noise that is picked up equally on both inputs is rejected because the difference is zero.

You specify the input configuration by setting switches on the board. The switches connect or disconnect the inverting side of the input signal to low-level ground. Refer to page 3-16 for information on setting the switches.

Notes: On the DAS-800, the

single-ended; ah signals are referred to a single low-level ground.

- A single-ended input configuration is appropriate if

- A differential input configuration is appropriate if you

channels are always configured as

If you are using BXP-16, EXP-16/A, or EXP-GP expansion MB-02 backplanes, you must configure the on-board analog input channels associated with the expansion boards or backplanes as

single-ended.

boards or

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Gains and Ranges

A DAS-800 board measures analog input signals in the range of f5 V. Each DAS-801 or DAS-802 board contains a programmable gain

amplifier (EGA), which allows you to measure analog input signals in one of several software-selectable unipolar and bipolar ranges. For each channel on a DAS-801 or DAS-802 board, you can specify one of five bipolar and four unipolar analog input ranges.

Table 2-1 lists the gains supported by DAS-800 Series boards and the analog input voltage range for each gain.

Table 2-l. Supported Gains

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Functional Description

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Note:

with protection against signals outside the specified analog input range. All DAS-800 Series boards can tolerate voltages up to f35 V and transients of several hundred volts without damaging the board.

When measuring signals at differential inputs, DAS-801 and DAS-802 boards can tolerate common-mode voltages up to f35 V and transients of several hundred volts without damaging the board; however, for normal operation of the board, make sure that the common-mode voltage is no more than 12 V - ((C / 2) x differential input voltage.

Channel Selection

You can use DAS-800 Series boards to acquire data from a single analog input channel or from a range of contiguous, on-board analog input channels using automatic channel scanning. These two methods of channel selection are described as follows:

Analog input channels on DAS-800 Series boards are provided

V,),

Single

initiate a conversion.

channel - You use software to specify a single channel and

where G is tbe gain and

is the

. Automatic channel scanning

and last channels in a range of contiguous, on-board channels (0 to 7).

The channels are sampled in order from first to last; the hardware

automatically increments the analog input multiplexer address shortly after the start of each conversion. When the last address is reached,

the multiplexer returns to the start address and the channels are

sampled again. For example, assume that the start channel is 4, the

stop channel is 7, and you want to acquire five samples. Your program reads data first from channel 4, then from channels 5, 6, and 7, and finally from channel 4 again.

The start channel can be higher than the stop channel. For example,

assume that the start channel is 7, the stop channel is 2, and you want

to acquire five samples. Your program reads data first from channel 7,

then from channels 0, 1, and 2, and finally from channel 7 again.

When using automatic channel scanning, all contiguous, on-board

channels must have the same gain (analog input range).

- You use software to specify the first

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Note:

that includes channels on expansion boards or MB Series backplanes, you can create a group of consecutive channels through software. tn addition, if your application requires non-consecutive channels or different gains for each channel, you can create a channel-gain list through software. The DAS-800 Series Function Call Driver provides functions for creating a group of consecutive channels or channel-gain list; refer to the

User’s you to set up a group of consecutive channels or channel-gain list; refer to Chapter 5 for more information. You can also set up a group of consecutive channels or channel-gain list using DAS-800 Series custom controls; refer to

Guide

Automatic channel scanning is a hardware feature. The functions used to create a group of consecutive channels or a channel-gain list emulate automatic channel scanning through software. Therefore, the maximum attainable conversion frequency is reduced when using a group of consecutive channels or a channel-gain list.

Channel Expansion

If you want to acquire

Guide

for more information. The Control Panel also allows

the VisualDAS Custom Controls User’s

for more information.

data

from a range of multiple channels

DAM00 Series Function Call Driver

Z-6

If you require additional analog input channels or signal conditioning for transducer inputs, you can use any combination of up to eight 16-channel EXP-16 expansion boards, eight 16-channel EXP-16/A expansion boards, and/or eight X-channel EXP-GP expansion boards to increase the number of available channels to 128. You can also use up to four MB-02 backplanes to increase the number of available channels to 68.

For the EXP-16, EXP-16/A. and EXP-GP, you attach the expansion boards in a daisy-chain configuration using the S-1800 or C-1800 cable. The first expansion board in the daisy chain is associated with on-board channel 0, the next expansion board is associated with

1, and so on. You specify the associated on-board channel by setting a

jumper on each expansion board. You can access any unused on-board

channels by attaching an STA-08 or STA-OBPGA screw terminal accessory to the last expansion board in the daisy-chain configuration.

on-board

Functional Description

channel

chapOZ.frm Black 7

Figure 2-2 illustrates a daisy-chain configuration of two EXP-16 expansion boards, one EXP-GP expansion board, and an STA-08 screw terminal accessory connected to a DAS-800 board.

Omboard channel 0

I I I I r I I I

D&3-600

Board

EXP.16

Figure 2-2. Channel Expansion

On-board On-board channel 1

EXP-16

channal2 chsnnsls 3 to 7

EXPQP

For information on attaching multiple MB-02 backplanes, refer to the ME Series User’s Guide.

Notes:

You must specify a single-ended input configuration for all

on-board channels associated with channels on EXP-16, EXP-16/A. or

EXP-GP expansion boards or MB-02 backplanes.

If you are using EXP-16, EXP- 16/A, or EXP-GP expansion boards or MB Series backplanes, the digital output lines of the DAS-800 Series board select the particular channel on the expansion board or backplane to read.

On-board

STA.08

Refer to the appropriate expansion board documentation for more information about the EXP-16, EXP-16/A, and EXP-GP expansion boards. Refer

to the ME Series User’s Guide

for more information about

the MB-02 backplane.

2-7

chap02-.frm Black 8

Conversion Clock Sources

The conversion clock source determines when each analog-to-digital (A/D) conversion is initiated. DAS-800 Series boards provide the following software-selectable conversion clock sources:

. Software -When using a software conversion clock, the host

computer issues a command to initiate a conversion. The host polls the board to determine if the conversion is complete. When the conversion is complete, the host reads the data from the ADC and returns the value. If the host reads data before the conversion is complete, the data will be invalid.

Software-initiated conversions are suitable for measuring DC voltages; however, in applications where you must accurately control the sampling rate (as when measuring time-varying signals), it is recommended that you use either an internal or an external hardware conversion clock source.

At power-up or system reset, the board assumes that conversions will be initiated through software.

. Hardware (internal clock source) -The internal clock source uses

the on-board 8254 counter/timer circuitry and a crystal-controlled

I MHz time base. The 8254 counter/timer circuitry is normally in an

idle state. When you start an analog input operation, a conversion is initiated immediately. The 8254 is loaded with its initial count value

and begins counting down. When the 8254 counts down to 0, another conversion is initiated and the process repeats.

Because the 8254 counter/timer uses a 1 MHz time base, each count represents 1 ps. For example, if you load a count of 25, the time

interval between conversions is 25 ps: if you load a count of 65536, the time interval between conversions is 65.536 ms.

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Functional Description

chap02Lfrm Black 9

The 8254 contains three counter/timers: C/TO, Cnl, and C/r2. If you are using a hardware internal clock source, the time base logic uses C/T1 and C/r2 in either normal or cascaded mode, as follows:

- Normal

of the 8254 counter/timer circuitry. Each time C/r2 reaches terminal count, a conversion is initiated. The time interval between conversions ranges from 25 FLS to 65.536 ms.

Cascaded Mode

C/r2 and C/r1 of the 8254 counter/timer circuitry. When CK2 counts down to 0, CR1 decrements by 1. Cn2 is reloaded with its count value and begins counting down again. Each time C/r2 counts down to 0, Cm1 decrements by 1. Each time both C/r2 and CR1 reach terminal count, a conversion is initiated. The time interval between conversions ranges from 25 ps to 1.2 hours.

Note:

system reset, the DA%800 board connects the clock input of C/r2 to the CPU bus clock divided by two. If you specify a hardware internal clock source through software, the DAS-800 board connects the clock inputs of C/T1 and CD2 to the 1 MHz time base. The DAS-801 and DAS-802 boards always connect the clock input of C/f2 to the

1 MHz time base.

Refer to page 2-17 for more information about the 8254 counter/timer circuitry.

Mode

- A software-selectable count is loaded into C/r2

- A software-selectable count is divided between

For compatibility with the DAS-8 board, on power-up or

. Hardware (external clock source) - An external clock source is

useful if you want to sample at rates not available with the 8254 counter/timer circuitry, if you want to sample at uneven intervals, or if you want to sample on the basis of an external event. An external clock also allows you to synchronize conversions on multiple boards to a common timing source.

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The external clock source is an externally applied TTL-compatible signal, which you attach to the INT-IN / XCLK pin (pin 24) of the main I/O connector. When you start an analog input operation, conversions are soume (and at every subsequent falling edge of the external clock

source), a conversion is initiated.

armed.

At the next falling edge of the external clock

Note:

use the INT-IN / XCLK pin (pin 24) to generate interrupts.

Figure 2-3 illustrates how conversions are initiated when using an internal

and an external clock source. (Note that Figure 2-3 assumes that you are not using a hardware trigger; refer to Figure 2-4 for an illustration of conversions when using a hardware trigger.)

If you are using a hardware external clock source, you cannot

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Figure 2-3. Initiating Conversions

Functional Description

chap02Lfrm Black 11

Notes: The ADC acquires data at a maximum of 40 kHz (one sample

every 25 ns). If you are using a hardware external clock, make sure that

the clock does not initiate conversions at a faster rate than the ADC can

handle.

To achieve full measurement accuracy when using a gain of 500, you

should limit me conversion frequency to a maximum of 25 kHz (one

sample every 40 its).

If you are acquiring samples from multiple channels. the maximum

sampling rate for each channel is equal to 40 kHz divided by the number

of channels.

The rate at which the computer can reliably read data from the board

depends on a number of factors, including your computer, the operating

system/environment, whether you are using expansion boards, the gains

of the channels, and software issues.

You can synchronize conversions on multiple DAS-800 Series boards to a

common, externally applied conversion clock. In addition, you can use a

DAS-801 or DAS-802 board as a timing master; the output of the OUT1 pin (pin 5) on the main I/O connector of the master board acts as an

external hardware conversion clock to any additional boards. You can use external circuitry, such as CEO on the 8254, to divide the rate of the master clock; this allows you to synchronize conversions on the

additional hoards to a rate different from that of the master board. Refer to page 4-13 for more information on synchronizing conversions on multiple

boards.

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Triggers

A trigger is an event that must occur before a DAS-800 Series board starts an analog input operation. You can use one of the following trigger

sources to trigger aa analog input operation:

. Software - When you start the analog input operation, conversions

begin

immediately.

. Hardware - You connect a digital trigger signal to the digital input

IP 1 /TRIG pin (pin 25) of the main I/O connector. The trigger event occurs when the board detects a rising edge on IP1 /TRIG.

The actual point at which conversions begin depends on whether you

are using an internal or external clock soorce. These considerations are described as follows:

Internal clock

source - The 8254 counter/timer circuitry remains idle until the trigger event occurs. When the trigger event occurs, the

board

initiates the first conversion immediately.

- Enrernal

clock

source - Conversions are armed when the trigger event occurs. At the next falling edge of the external clock source, the board initiates the first conversion.

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Functional Description

chap02-.frm Black 13

Figure 2-4 illustrates how conversions are started when using a hardware trigger.

External Clock source

Figure 24. Initiating Conversions

with

a Hardware Trigger

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Hardware Gates

A hardware gate is an externally applied digital signal that determines whether conversions occur. You connect the gate signal to the IPl /TRIG pin (pin 25) on the main I/O connector. DAS-800 Series boards support a positive gate only. Therefore, if the hardware gate is enabled and the

signal to IPl /TRIG is high, conversions occur; if the signal to IPl /

TRIG is low. conversions are inhibited.

Note:

You cannot use the hardware gate with a hardware trigger. However, the gate signal itself can act as a trigger. If the gate signal is low when the software starts the analog input operation, the board waits until the gate signal goes high before conversions begin.

When using the hardware gate, the way conversions are synchronized depends on whether you are using a hardware external clock or a hardware internal clock, as follows:

. External

clock

- The signal from the external clock continues

uninterrupted while the gate signal is low; therefore, conversions are

synchronized to the external clock.

. Internal clock - The 8254 does not count while the gate signal is low.

Whenever the gate signal goes high, the 8254 is loaded with its initial count value and starts counting; therefore, conversions are synchronized to the gate signal.

Figure 2-5 illustrates how to use the hardware gate with both an external clock and an internal clock.

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Functional Description

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sonware starts ths

operation -b

3rd convmsion

2nd conversion

/ /

p-r . . . . . . * . . . . .

at wnverslon , (Intcmsl clock)

Note:

analog trigger, you can program an analog trigger through software, using one of the analog input channels as the trigger channel. The DAS-800 Series Function Call Driver provides functions for an analog trigger; refer to

the DAS-800 Series Funciion Call Driver User’s Guide

information. The Control Panel also allows you to set up an analog trigger; refer to Chapter 5 for more information. You can also set up an analog trigger using DAS-800 Series custom controls; refer to the

VisualDAS

2nd mnvwston (Inkmel clock)

Figure 2-5. Hardware Gate

t 3rd l2dverslon (Internal clock)

4th converslbn (Internalclock)

A-

Although DAS-800 Series boards do not provide a hardware-based

for more

Custom

Controls Lrser’x Guide

for more information.

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+ 101 hidden pages

Tektronix DAS-800 Series Users Guide

Specifications and Main Features

Frequently Asked Questions

User Manual