USB-2537
16-bit, 1 MS/s, High-Speed DAQ Board

User's Guide

May 2016. Rev 8A© Measurement Computing Corporation

Trademark and Copyright Information
Measurement Computing Corporation, InstaCal, Universal Library, and the Measurement Computing logo areeither trademarks or registered trademarks of Measurement Computing Corporation. Refer to the Copyrights &Trademarks section on mccdaq.com/legal for more information about Measurement Computing trademarks.
Other product and company names mentioned herein are trademarks or trade names of their respective
companies.
© 2016 Measurement Computing Corporation. All rights reserved. No part of this publication may be
reproduced, stored in a retrieval system, or transmitted, in any form by any means, electronic, mechanical, by
photocopying, recording, or otherwise without the prior written permission of Measurement Computing
Corporation.
NoticeMeasurement Computing Corporation does not authorize any Measurement Computing Corporation product for
use in life support systems and/or devices without prior written consent from Measurement Computing
Corporation. Life support devices/systems are devices or systems that, a) are intended for surgical implantation
into the body, or b) support or sustain life and whose failure to perform can be reasonably expected to result ininjury. Measurement Computing Corporation products are not designed with the components required, and are
not subject to the testing required to ensure a level of reliability suitable for the treatment and diagnosis ofpeople.

HM USB-2537.docx

Table of Contents
Preface

About this User's Guide ....................................................................................................................... 5
What you will learn from this user's guide ......................................................................................................... 5
Conventions in this user's guide ......................................................................................................................... 5
Where to find more information ......................................................................................................................... 5
Chapter 1

Introducing the USB-2537 .................................................................................................................... 6
Overview: USB-2537 features ............................................................................................................................ 6
Chapter 2

Installing the USB-2537 ........................................................................................................................ 7
Unpacking the USB-2537 ................................................................................................................................... 7
Installing the software ........................................................................................................................................ 7
Installing the hardware ....................................................................................................................................... 7
Configuring the hardware ................................................................................................................................... 8Signal connections .............................................................................................................................................. 968-pin SCSI connector (P5) .............................................................................................................................................1040-pin header connectors (J5, J6, J7, J8)..........................................................................................................................13
Four-channel TC terminal block (TB7) ...........................................................................................................................16

Cabling ............................................................................................................................................................. 17
Field wiring and signal termination .................................................................................................................. 17
Chapter 3

Functional Details ...............................................................................................................................18
Board components ............................................................................................................................................ 18
Functional block diagram ................................................................................................................................. 20
Synchronous I/O – mixing analog, digital, and counter scanning .................................................................... 21
Analog input ..................................................................................................................................................... 21
Analog input scanning .....................................................................................................................................................21

Thermocouple input .......................................................................................................................................... 23
Tips for making accurate temperature measurements ......................................................................................................24

Analog output ................................................................................................................................................... 24
Digital I/O ......................................................................................................................................................... 25
Digital input scanning ......................................................................................................................................................25
Digital outputs and pattern generation .............................................................................................................................26

Triggering ......................................................................................................................................................... 26
Hardware analog triggering .............................................................................................................................................26
Digital triggering..............................................................................................................................................................26
Software-based triggering ................................................................................................................................................26
Stop trigger modes ...........................................................................................................................................................27
Pre-triggering and post-triggering modes ........................................................................................................................27

Counter inputs .................................................................................................................................................. 27
Mapped channels .............................................................................................................................................................28
Counter modes .................................................................................................................................................................28
Debounce modes ..............................................................................................................................................................29
Encoder mode ..................................................................................................................................................................32

Timer outputs.................................................................................................................................................... 35
Example: Timer outputs ...................................................................................................................................................35

Using detection setpoints for output control ..................................................................................................... 36
What are detection setpoints? ..........................................................................................................................................36
Setpoint configuration overview ......................................................................................................................................36
Setpoint configuration......................................................................................................................................................373

USB-2537 User's Guide

Using the setpoint status register......................................................................................................................................38
Examples of control outputs ............................................................................................................................................39
Detection setpoint details .................................................................................................................................................42
FIRSTPORTC, DAC, or timer update latency .................................................................................................................43

Mechanical drawing ......................................................................................................................................... 44
Chapter 4

Calibrating the USB-2537 ...................................................................................................................45
Chapter 5

Specifications ......................................................................................................................................46
Analog input ..................................................................................................................................................... 46
Accuracy ..........................................................................................................................................................................46
Thermocouples ................................................................................................................................................................47

Analog outputs.................................................................................................................................................. 47
Digital input/output........................................................................................................................................... 48
Counters ............................................................................................................................................................ 48
Input sequencer ................................................................................................................................................. 49
Trigger sources and modes ............................................................................................................................... 49
Frequency/pulse generators .............................................................................................................................. 50
Power consumption .......................................................................................................................................... 50
External power .................................................................................................................................................. 50
USB specifications ........................................................................................................................................... 50
Environmental .................................................................................................................................................. 51
Mechanical ....................................................................................................................................................... 51
Signal I/O connectors ....................................................................................................................................... 51
68-pin SCSI connector (P5) .............................................................................................................................................52
40-pin header connectors .................................................................................................................................................54
TC connector (TB7) .........................................................................................................................................................57

4

Preface

About this User's Guide
What you will learn from this user's guideThis user's guide describes the Measurement Computing USB-2537 data acquisition device and lists the
specifications.

Conventions in this user's guide
For more information
Text presented in a box signifies additional information and helpful hints related to the subject matter you arereading.
Caution! Shaded caution statements present information to help you avoid injuring yourself and others,
damaging your hardware, or losing your data.
bold text

Bold text is used for the names of objects on a screen, such as buttons, text boxes, and check boxes.

italic text

Italic text is used for the names of manuals and help topic titles, and to emphasize a word or phrase.

Where to find more information
For additional information relevant to the operation of your hardware, refer to the Documents subdirectory
where you installed the MCC DAQ software (C:\Program Files\Measurement Computing\DAQ by default), or
search for your device on our website at www.mccdaq.com.

5Chapter 1

Introducing the USB-2537
Overview: USB-2537 features
The USB-2537 board is a multifunction measurement and control board that is supported under popular
Microsoft® Windows® operating systems.
The USB-2537 provides the following features:








1

32 differential or 64 single-ended analog inputs with 16-bit resolution.
o Software-selectable analog input ranges: ±10 V, ±5 V, ±2 V, ±1 V, ±0.5 V, ±0.2 V, ±0.1V.
o Up to four thermocouple (TC) inputs
Four 16-bit, 1 MHz analog outputs with an output range of –10 V to +10 V
24 high-speed digital I/O lines
o Up to 4 MHz scanning on all digital input lines1.
Two timer outputs
Four 32-bit counters
Synchronous analog I/O, digital I/O, and counter/timer I/O operations

Higher rates—up to 12 MHz—are possible depending on the platform and the amount of data being transferred.

6

Chapter 2

Installing the USB-2537
Unpacking the USB-2537
As with any electronic device, you should take care while handling to avoid damage from static
electricity. Before removing the USB-2537 from its packaging, ground yourself using a wrist strap or by simply
touching the computer chassis or other grounded object to eliminate any stored static charge.
If any components are missing or damaged, notify Measurement Computing Corporation immediately byphone, fax, or e-mail:

Phone: 508-946-5100 and follow the instructions for reaching Tech Support
Fax: 508-946-9500 to the attention of Tech Support
Email: techsupport@mccdaq.com

For international customers, contact your local distributor. Refer to the International Distributors section on our
web site at www.mccdaq.com/International.

Installing the software
Refer to the MCC DAQ Quick Start and the USB-2537 product page on our website for information about theavailable software.
Install the software before you install your device
The driver needed to run the USB-2537 is installed with the software. Therefore, you need to install thesoftware package you plan to use before you install the hardware.

Installing the hardware
To connect the USB-2537 to your system, turn your computer on, and connect the USB cable to a USB port onyour computer or to an external USB hub that is connected to your computer. The USB cable provides powerand communication to the USB-2537.
When you connect the USB-2537 to a computer for the first time, a Found New Hardware dialog opens when
the operating system detects the device. When the dialog closes, the installation is complete.
The power LED (bottom LED) blinks during device detection and initialization, and then remains on as long as
the USB-2537 has sufficient power. If the power provided from the USB is not sufficient, the LED turns off,
indicating you need a PS-9V1AEPS-2500 power supply.
When the board is first powered on, there is usually a momentary delay before the power LED blinks or turnson.
Connect external power, if used, before connecting the USB cable to the computer
If you are using a PS-9V1AEPS-2500 power supply, connect the external power cable to the USB-2537 before
connecting the USB cable to the computer. This allows the USB-2537 to inform the host computer (when the
USB cable is connected) that the board requires minimal power from the computer’s USB port.
In general, all standoffs should be used to mount the board to a metal frame.

7

USB-2537 User's Guide

Installing the USB-2537

The standoff at thislocation connects to theinternal chassis plane forshunting electrostatic
discharge.

The standoff at this location
connects to the USB chassis
for shunting electrostatic
discharge.

Caution! Do not disconnect any device from the USB bus while the computer is communicating with theUSB-2537, or you may lose data and/or your ability to communicate with the USB-2537.

Configuring the hardware
All hardware configuration options on the USB-2537 are software-controlled. You can select some of theconfiguration options using InstaCal, such as the analog input configuration (64 single-ended or 32 differential
channels), and the edge used for pacing when using an external clock. Once selected, any program that uses the
Universal Library initializes the hardware according to these selections.
You need a PS-9V1AEPS-2500 power supply (sold separately) when there is insufficient power from the USB
port. However, you can use this power supply in any scenario.
Caution! Avoid redundant connections. Ensure there is no signal conflict between SCSI pins and theassociated header pin (J5 - J8). Also make sure there is no conflict between theTB7 TC
connections and the SCSI and/or the 40-pin header connections.
Failure to do so could possibly cause equipment damage and/or personal injury.
Also, turn off power to all devices connected to the system before making connections. Electricalshock or damage to equipment can result even under low-voltage conditions.
Information on signal connections
General information regarding signal connection and configuration is available in the Guide to DAQ Signal
Connections. This document is available for download from www.mccdaq.com/support/DAQ-SignalConnections.aspx).
Caution! Always handle components carefully, and never touch connector pins or circuit components unless
you are following ESD guidelines in an appropriate ESD-controlled area. These guidelines include
using properly-grounded mats and wrist straps, ESD bags and cartons, and related procedures.
Avoid touching board surfaces and onboard components. Only handle boards by their edges. Make
sure the USB-2537 does not come into contact with foreign elements such as oils, water, andindustrial particulate.
The discharge of static electricity can damage some electronic components. Semiconductor
devices are especially susceptible to ESD damage.

8

USB-2537 User's Guide

Installing the USB-2537

Signal connections
The following table lists board connectors, applicable cables, and compatible accessory products.
Board connectors, cables, and compatible hardware
Parameter

Specification

Connector types

Main connector: 68-pin standard "SCSI type III" female connector
Auxiliary connectors: Four, 40-pin header connectors
68-pin SCSI connector:
 CA-68-3R — 68-pin ribbon cable; 3 feet.
 CA-68-3S — 68-pin shielded round cable; 3 feet.
 CA-68-6S — 68-pin shielded round cable; 6 feet
40-pin header connectors:
 C40FF-x
Using CA-68-3R, CA-68-3S, or CA-68-6S cables: TB-100 terminal board
Using the C40FF-x cable:
 CIO-MINI40
Terminal board: TB-101; mounts directly onto the header connectors

Compatible cables

Compatible accessory products

9USB-2537 User's Guide

Installing the USB-2537

68-pin SCSI connector (P5)The 68-pin SCSI connector—labeled P5 on the board—provides 16 single-ended analog channels or eight
differential analog channels. Refer to the "40-pin header connector" section starting on page 13 to learn thepinouts for accessing up to 64 single-ended/32 differential analog channels using the P5 and P6 connectors.
Caution! Avoid redundant connections. Make sure there is no signal conflict among the SCSI pins, the 40pin header connector pins (J5 - J8), and the TB7 TC connections. Failure to do so could possibly
cause equipment damage and/or personal injury.
SCSI connector P5 single-ended pinout
Signal name

Pin

Pin

Signal name

ACH0
AGND
ACH9

68
67
66





34
33
32

ACH8
ACH1

ACH2
AGND

65
64




31
30

ACH11
SGND
ACH12

63
62
61





29
28
27

ACH5
AGND

60
59




26
25

ACH14
ACH7

58
57




24
23

XDAC3
XDAC2

56
55
54





22
21
20

53
52




19
18

A3
A5

51
50




17
16

A7
B1
B3

49
48
47





15
14
13

B5
B7

46
45




12
11

C1
C3

44
43




10
9

C5
C7
GND

42
41
40





8
7
6

CNT1
CNT3

39
38




5
4

TMR1
GND
GND

37
36
35





3
2
1

NEGREF (reserved for self-calibration)
GND
A1

10

AGND
ACH10
ACH3
AGND
ACH4
AGND
ACH13
ACH6
AGND
ACH15
XDAC0
XDAC1
POSREF (reserved for self-calibration)
+5 V
A0
A2
A4
A6
B0
B2
B4
B6
C0
C2
C4
C6
TTL TRG
CNT0
CNT2
TMR0
XAPCR
XDPCR

USB-2537 User's Guide

Installing the USB-2537

SCSI connector P5 differential pinout
Signal name

Pin

Pin

Signal name

ACH0 HIAGND
ACH1 LO

68
67
66





34
33
32

ACH0 LO

ACH2 HI
AGND

65
64




31
30

ACH3 LO
SGND

63
62




29
28

ACH4 LO
ACH5 HI
AGND

61
60
59





27
26
25

ACH6 LO
ACH7 HI

58
57




24
23

XDAC3
XDAC2

56
55




22
21

NEGREF (reserved for self-calibration)
GND
A1

54
53
52





20
19
18

A3
A5

51
50




17
16

A7
B1

49
48




15
14

B3
B5
B7

47
46
45





13
12
11

C1
C3

44
43




10
9

C5
C7

42
41




8
7

GND
CNT1
CNT3

40
39
38





6
5
4

TMR1
GND

37
36




3
2

GND

35



1

11

ACH1 HIAGND
ACH2 LO
ACH3 HIAGND
ACH4 HIAGND
ACH5 LO
ACH6 HIAGND
ACH7 LOXDAC0
XDAC1
POSREF (reserved for self-calibration)
+5 V
A0
A2
A4
A6
B0
B2
B4
B6
C0
C2
C4
C6
TTL TRG
CNT0
CNT2
TMR0
XAPCR
XDPCR

USB-2537 User's Guide

Installing the USB-2537

TB-100 terminal board connector to SCSI connector pinout
SCSI connector pinout assignments for TB-100(differential analog signals in parentheses)
TB2 screw terminal

SCSI pin

TB1 screw terminal

SCSI pin

+5V
GND
A0
A1
A2
A3
A4
A5
A6
A7
B0
B1
B2
B3
B4
B5
B6
B7
C0
C1
C2
C3
C4
C5
C6
C7
TTLTRG
GND
CNT0
CNT1
CNT2
CNT3
TMR0
TMR1
XDPCR
GND

19

ACH0 (ACH0 HI)
ACH8 (ACH0 LO)
AGND
ACH1 (ACH1 HI)
ACH9 (ACH1 LO)
AGND
ACH2 (ACH2 HI)
ACH10 (ACH2 LO)
AGND
ACH3 (ACH3 HI)
ACH11 (ACH3 LO)
AGND
ACH4 (ACH4 HI)
ACH12 (ACH4 LO)
AGND
ACH5 (ACH5 HI)
ACH13 (ACH5 LO)
AGND
ACH6 (ACH6 HI)
ACH14 (ACH6 LO)
AGND
ACH7 (ACH7 HI)
ACH15 (ACH7 LO)
XDAC3
SGND
POSREF (reserved for self-calibration)
XDAC2
NEGREF (reserved for self-calibration)
AGND
XDAC0
AGND
XDAC1
AGND
XAPCR
GND
EGND

68
34
**
33
66
**
65
31
**
30
63
**
28
61
**
60
26
**
25
58
**
57
23
56
62
20
55
54
**
22
**
21
**
2
**
†

*
18
52
17
51
16
50
15
49
14
48
13
47
12
46
11
45
10
44
9
43
8
42
7
41
6

*
5
39
4
38
3
37
1

*
* Digital common ground pins on the SCSI connector are: 35, 36, and 40.
** Analog common ground pins on the SCSI connector are: 24, 27, 29, 32, 59, 64, and 67.
† EGND is connected to the SCSI connector shell.

12

USB-2537 User's Guide

Installing the USB-2537

40-pin header connectors (J5, J6, J7, J8)
Analog channels pinout (J5 and J6)

This edge of the header is closest to the center of theboard. Pins 2 and 40 are labeled on the board silkscreen.

Header connector J5 and J6 single-ended pinout
Analogchannel

Pin

J5

Pin

AnalogchannelAnalogchannel

Pin

J6

Pin

Analogchannel

ACH27

1

2

ACH19

ACH43

1

2

ACH59

ACH26

3

4

ACH18

ACH35

3

4

ACH51

AGND

5

6

AGND

AGND

5

6

ACH58

ACH3

7

8

ACH11

ACH42

7

8

ACH50

ACH2

9

10

ACH10

ACH34

9

10

ACH57

ACH17

11

12

ACH25

AGND

11

12

ACH49

ACH16

13

14

ACH24

ACH41

13

14

ACH56

ACH1

15

16

ACH9

ACH33

15

16

ACH48

ACH0

17

18

ACH8

ACH40

17

18

AGND

AGND

19

20

AGND

ACH32

19

20

ACH63

ACH23

21

22

ACH31

ACH47

21

22

ACH55

ACH22

23

24

ACH30

ACH39

23

24

AGND

ACH7

25

26

ACH15

ACH46

25

26

ACH62

ACH6

27

28

ACH14

ACH38

27

28

ACH54

AGND

29

30

ACH21

AGND

29

30

ACH61

ACH29

31

32

ACH20

ACH45

31

32

ACH53

ACH28

33

34

ACH5

ACH37

33

34

ACH60

ACH13

35

36

ACH4

ACH44

35

36

ACH52

ACH12

37

38

AGND

ACH36

37

38

AGND

AGND

39

40

AGND

AGND

39

40

AGND

13

USB-2537 User's Guide

Installing the USB-2537

Header connector J5 and J6 differential pinout
Analogchannel

Pin

J5

Pin

AnalogchannelAnalogchannel

Pin

J6

Pin

Analogchannel

ACH11 LO

1

2

ACH11 HI

ACH19 LO

1

2

ACH27 LO

ACH10 LO

3

4

ACH10 HI

ACH19 HI3

4

ACH27 HI

AGND

5

6

AGND

AGND

5

6

ACH26 LO

ACH3 HI7

8

ACH3 LO

ACH18 LO

7

8

ACH26 HI

ACH2 HI910

ACH2 LO

ACH18 HI910

ACH25 LO

ACH9 HI11

12

ACH9 LO

AGND

11

12

ACH25 HI

ACH8 HI13

14

ACH8 LO

ACH17 LO

13

14

ACH24 LO

ACH1 HI15

16

ACH1 LO

ACH17 HI15

16

ACH24 HI

ACH0 HI1718

ACH0 LO

ACH16 LO

17

18

AGND

AGND

19

20

AGND

ACH16 HI19

20

ACH31 LO

ACH15 HI21

22

ACH15 LO

ACH23 LO21

22

ACH31 HI

ACH14 HI23

24

ACH14 LO

ACH23 HI

23

24

AGND

ACH7 HI25

26

ACH7 LO

ACH22 LO25

26

ACH30 LO

ACH6 HI27

28

ACH6 LO

ACH22 HI27

28

ACH30 HI

AGND

29

30

ACH13 HI

AGND

29

30

ACH29 LO

ACH13 LO31

32

ACH12 HI

ACH21 LO31

32

ACH29 HI

ACH12 LO33

34

ACH5 HI

ACH21 HI33

34

ACH28 LO

ACH5 LO

35

36

ACH4 HI

ACH20 LO

35

36

ACH28 HI

ACH4 LO

37

38

AGND

ACH20 HI

37

38

AGND

AGND

39

40

AGND

AGND

39

40

AGND

14

USB-2537 User's Guide

Installing the USB-2537

Digital ports, counters, timers, DACs, triggers, and pacer clocks pinout (J7 and J8)
You can use the 40-pin connector headers labeled J7 and J8 to connect digital ports, counters, timers, DACs,
triggers, pacer clocks, and other signals.
Header connector J7 and J8 pinout
Digital channel

Pin

J7

Pin

Digital channel

GND

1

2

XAPCR

A0

3

4

A1

5

A2

Signal

Pin

J8

Pin

Signal

+13 V

1

2

-13 V

A4

NC

3

4

NC

6

A5

AGND

5

6

AGND

7

8

A6

XDAC0

7

8

XDAC2

A3

9

10

A7

XDAC1

9

10

XDAC3

GND

11

12

TTL TRG

AGND

11

12

AGND

B0

13

14

B4

SelfCal

13

14

SGND

B1

15

16

B5

AGND

15

16

AGND

B2

17

18

B6

TTL TRG

17

18

XDPCR

B3

19

20

B7

XAPCR

19

20

GND (digital)

GND

21

22

+5 V

GND (digital)

21

22

GND (digital)

C0

23

24

C4

NC

23

24

NC

C1

25

26

C5

+5 V

25

26

AUX PWR

C2

27

28

C6

NC

27

28

NC

C3

29

30

C7

NC

29

30

NC

GND

31

32

TMR1

NC

31

32

NC

TMR0

33

34

CNT1

NC

33

34

NC

CNT0

35

36

CNT3

NC

35

36

NC

CNT2

37

38

GND

NC

37

38

NC

GND

39

40

GND

NC

39

40

NC

15

USB-2537 User's Guide

Installing the USB-2537

Using C40FF-x cables to obtain 40-pin female connectors
In this example, a C40FF-x cable is connected to all of the 40-pin headers (J5, J6, J7, and J8). The result is four
female 40-pin connectors that together have more signal connectivity than the SCSI connector.
40-pin female connectors

C40FF-x header cables

USB cable

Figure 1. Four C40FF-x cables connected to J5 through J8 40-pin connectors

Four-channel TC terminal block (TB7)
You can use the TB7 terminal block to connect up to four thermocouples. The first TC channel uses ACH0
(analog channel 0) for its positive (+) lead, and ACH8 for its negative (–) lead. The second TC channel uses
ACH1 and ACH9, and so on, as indicated in Figure 2.
TC CH 0

TC CH 1

TC CH 2

TC CH 3Standoff
AGND
ACH0 +
ACH8 (-)

ACH1 +
ACH9 (-)
ACH2 +
ACH10 (-)
ACH3 +
ACH11 (-)

Figure 2. TB7 pinout

16

USB-2537 User's Guide

Installing the USB-2537

Cabling
Use a CA-68-3R 68-pin ribbon expansion cable (Figure 3), or a CA-68-3S (3-foot) or CA-68-6S (6-foot) 68-pin
shielded expansion cable (Figure 4) to connect signals to the 68-pin SCSI connector.

34

68

1

35

34

68

1

35

The stripe
identifies pin # 1

Figure 3. CA-68-3R cable
34

68

1

35

34

68

1

35

Figure 4. CA-68-3S and CA-68-6S cableUse one or more C40FF-x- ribbon cable(s) (Figure 5) to connect signals to one or more of the 40-pin header
connectors.

2

1

40

39

The red stripe
identifies pin # 1

40-pin Female
IDC Connector

2

1

40

39

40-pin Female
IDC Connector

Figure 5. C40FF-x cable

Field wiring and signal termination
You can use the following screw terminal board to terminate field signals and route them into the USB-2537
board using the CA-68-3R, CA-68-3S, or CA-68-6S cable:


TB-100: Termination board with screw terminals.

A 19-inch rack mount kit (RM-TB-100) for the TB-100 termination board is also available.
You can use the following screw terminal board with the C40FF-x cable.


CIO-MINI40: 40-pin screw terminal board.

Details on these products are available on our web site.
17

Chapter 3

Functional Details
This chapter contains detailed information on all of the features available from the board, including:a diagram and explanations of physical board components
a functional block diagram
information on how to use the signals generated by the board
diagrams of signals using default or conventional board settings

Board components
These USB-2537 components are shown in Figure 6.







One USB port
One external power connector
One 68-pin SCSI connector
Four 40-pin headers (J5, J6, J7, and J8)
One four-channel TC screw terminal block
Two LED indicators (USB and power)

J6

TB7

J5

J7
J8

P5

External power
supply connector
USB 2.0 port

USB LEDPower LED

Figure 6. USB-2537 components

18USB-2537 User's Guide

Functional Details

SCSI - 68 pin (P5) connector
The 68-pin SCSI connector includes pins for the following:













16 single-ended/eight differential analog inputs (64 single-ended/32 differential analog inputs available
only from J5 and J6 40-pin connectors)
Four analog outputs
24 digital I/O
Four counter inputs
Two timer outputs
Input scan pacer clock I/O
Output scan pacer clock I/O
TTL trigger
self calibration+5 VDC
analog commons
digital commons

40-pin headers (J5, J6, J7, J8)
The four 40-pin headers provide alternative connections to the SCSI connector signals. You can get a female
connector for each header by connecting a C40FF-x cable to each header.
9-slot screw terminal (TB7)
You can use the on-board screw terminal connector (TB7) to connect up to four TC inputs. TB7 uses thefollowing analog channels to obtain its four differential channels:TC CH0: CH 0 (+); CH 8 (-)
TC CH1: CH 1 (+); CH 9 (-)
TC CH2: CH 2 (+); CH 10 (-)
TC CH3: CH 3 (+); CH 11 (-)

When using the thermocouple channels, do not connect signals to the associated channels on the SCSI
connector or J5.
External power connector
Although the USB-2537 is powered by a USB port on a host PC, an external power connector is available when
the host PC’s USB port cannot supply adequate power, or if you prefer to use a separate power source.
Connect the optional PS-9V1AEPS-2500 power supply to the external power supply connector. This power
supply plugs into a standard 120 VAC outlet and supplies 9 VDC, 1 A power to the USB-2537.

19

USB-2537 User's Guide

Functional Details

Functional block diagram
Device functions are illustrated in the block diagram shown in Figure 7.

Figure 7. USB-2537 functional block diagram20

USB-2537 User's Guide

Functional Details

Synchronous I/O – mixing analog, digital, and counter scanning
The USB-2537 can read analog, digital, and counter inputs, while generating up to four analog outputs anddigital pattern outputs at the same time. Digital and counter inputs do not affect the overall A/D rate because
these inputs use no time slot in the scanning sequencer.
For example, one analog input channel can be scanned at the full 1 MHz A/D rate along with digital and counter
input channels. Each analog channel can have a different gain, and counter and digital channels do not needadditional scanning bandwidth as long as there is at least one analog channel in the scan group.
Digital input channel sampling is not done during the "dead time" of the scan period where no analog sampling
is being done either.

Analog input
The USB-2537 has a 16-bit, 1-MHz A/D coupled with 64 single-ended, or 32 differential analog inputs.
Software programmable ranges provide inputs from ±10 V to ±100 mV full scale.

Analog input scanning
The USB-2537 has several scanning modes to address various applications. You can load the 512-location scanbuffer with any combination of analog input channels. All analog input channels in the scan buffer are measured
sequentially at 1 µs per channel by default.
For example, in the fastest mode, with a 1 µs settling time for the acquisition of each channel, a single analog
channel can be scanned continuously at 1 MS/s; two analog channels can be scanned at 500 kS/s each;
16 analog input channels can be scanned at 62.5 kS/s.
Settling time
For most applications, leave the settling time at its default of 1 µs.
However, if you are scanning multiple channels, and one or more channels are connected to a high-impedancesource, you may get better results by increasing the settling time. Remember that increasing the settling reduces
the maximum acquisition rate.
You can set the settling time to 1 µs, 5 µs, 10 µs, or 1 ms.
Example: Analog channel scanning of voltage inputs
Figure 8 shows a simple acquisition. The scan is programmed pre-acquisition and is made up of six analog
channels (Ch0, Ch1, Ch3, Ch4, Ch6, and Ch7). Each of these analog channels can have a different gain. The
acquisition is triggered and the samples stream to the PC. Using the default settling time, each analog channel
requires one microsecond of scan time—therefore the scan period can be no shorter than 6 µs for this example.
The scan period can be made much longer than 6 µs—up to 1 s. The maximum scan frequency is 1 divided by
6 µs, or 166,666 Hz.

Figure 8. Analog channel scan of voltage inputs example

21

USB-2537 User's Guide

Functional Details

Example: Analog channel scanning of voltage and temperature inputs
Figure 9 shows a programmed pre-acquisition scan made up of six analog channels (Ch0, Ch1, Ch5, Ch11,
Ch12, Ch13). Each of these analog channels can have a different gain. You can program channels 0 and 1 todirectly measure TCs.
In this mode, oversampling is programmable up to 16384 oversamples per channel in the scan group. When
oversampling is applied, it is applied to all analog channels in the scan group, including temperature and voltage
channels. Digital channels are not oversampled.
If you want 256 oversamples, then each analog channel in the scan group takes 256 µs, and the returned 16-bit
value represents an average of 256 consecutive 1 µs samples of that channel. The acquisition is triggered and16-bit values—each representing an average of 256—stream to the PC via the USB cable. Since two of thechannels in the scan group are temperature channels, you need the acquisition engine to read a cold-junctioncompensation (CJC) temperature every scan.

Figure 9. Analog channel scanning of voltage and temperature inputs example

Since the targeted number of oversamples is 256 in this example, each analog channel in the scan grouprequires 256 microseconds to return one 16-bit value. The oversampling is also done for CJC temperature
measurement channels, making the minimum scan period for this example 7 X 256 µs, or 1792 µs. The
maximum scan frequency is the inverse of this number, 558 Hz.
For accurate measurements, you must associate TC and CJC channels properly
The TC channels must immediately follow their associated CJC channels in the channel array. For accurate TC
readings, associate CJC0 with TC0, CJC1 with TC1 and TC2, and CJC2 with TC3.
Example: Analog and digital scanning, once per scan mode
The scan is programmed pre-acquisition and is made up of six analog channels (Ch0, Ch2, Ch5, Ch11, Ch13,
Ch15) and four digital channels (16-bits of digital IO, three counter inputs.) Each of the analog channels canhave a different gain.
The acquisition is triggered and the samples stream to the PC via the USB cable. Each analog channel requires
one microsecond of scan time. Therefore, the scan period can be no shorter than 6 µs for this example. All of
the digital channels are sampled at the start of scan and do not require additional scanning bandwidth as long as
there is at least one analog channel in the scan group. The scan period can be made much longer than 6 µs, up to
1 second. The maximum scan frequency is one divided by 6 µs, or 166,666 Hz.

Figure 10. Analog and digital scanning, once per scan mode example

22USB-2537 User's Guide

Functional Details

The counter channels may return only the lower 16-bits of count value if that is sufficient for the application.
They could also return the full 32-bit result if necessary. Similarly, the digital input channel could be the full24 bits if desired or only eight bits if that is sufficient. If the three counter channels are all returning 32-bit
values and the digital input channel is returning a 16-bit value, then 13 samples are being returned to the PC
every scan period, with each sample being 16-bits. The 32-bit counter channels are divided into two 16-bit
samples—one for the low word, and the other for the high word. If the maximum scan frequency is 166,666 Hz,then the data bandwidth streaming into the PC is 2.167 MS/s. Some slower PCs may have a problem with data
bandwidths greater than 6 MS/s. The USB-2537 has an onboard 1 MS buffer for acquired data.
Example: Sampling digital inputs for every analog sample in a scan group
The scan is programmed pre-acquisition and is made up of six analog channels (Ch0, Ch2, Ch5, Ch11, Ch13,
Ch15) and four digital channels (16-bits of digital input, three counter inputs.) Each of the analog channels canhave a different gain.
The acquisition is triggered and the samples stream to the PC via the USB cable. Each analog channel requires
one microsecond of scan time therefore the scan period can be no shorter than 6 µs for this example. All of thedigital channels are sampled at the start of scan and do not require additional scanning bandwidth as long as
there is at least one analog channel in the scan group. The 16-bits of digital input are sampled for every analog
sample in the scan group. This allows up to 1 MHz digital input sampling while the 1 MHz analog sampling
bandwidth is aggregated across many analog input channels.
The scan period can be made much longer than 6 µs—up to 1 second. The maximum scan frequency is one
divided by 6 µs, or 166,666 Hz. Note that digital input channel sampling is not done during the "dead time" ofthe scan period where no analog sampling is being done either.

Figure 11. Analog and digital scanning, once per scan mode example

If the three counter channels are all returning 32-bit values and the digital input channel is returning a 1-bit
value, then 18 samples are returned to the PC every scan period, with each sample being 16-bits. Each 32-bit
counter channel is divided into two 16-bit samples—one for the low word and the other for the high word. If the
maximum scan frequency is 166,666 Hz, then the data bandwidth streaming into the PC is 3 MS/s. Some slower
PCs may have a problem with data bandwidths greater than 6 MS/s.
The USB-2537 has an onboard 1 MS buffer for acquired data.

Thermocouple input
You can configure up to four analog inputs on the USB-2537 to accept a TC input. Built-in cold-junction
sensors are provided for each of the screw-terminal connectors, and any TC type can be attached to any of thefour thermocouple channels.
When measuring TCs, the USB-2537 can operate in an averaging mode, taking multiple readings on eachchannel, applying digital filtering and cold-junction compensation, and then converting the readings totemperature.
As a result, the USB-2537 measures channels with TCs attached at a rate from 50 Hz to 10 kHz, depending on
how much over-sampling is selected.
Additionally, a rejection frequency can be specified in which over sampling occurs during one cycle of either
50 Hz or 60 Hz, providing a high level of 50 Hz or 60 Hz rejection.
23

USB-2537 User's Guide

Functional Details

Tips for making accurate temperature measurements









Use as much oversampling as possible.
Warm up the USB-2537 for 60 minutes—including TC wires—so that it is thermally stabilized. Thiswarm-up time enables the CJC thermistors to more accurately measure the junction at the terminal block.
Make sure the surrounding environment is thermally stabilized and ideally around 20 °C to 30 °C. If theboard’s ambient temperature is changing due to a local heating or cooling source, then the TC junction
temperature may be changing and the CJC thermistor will have a larger error.
Use small-diameter, instrument-grade TC wire. Small diameter TC wire has less effect on the TC junction
at the terminal block because less heat is transferred from the ambient environment to the junction.
Use shielded TC wire (see "Shielding" below) with the shield connected to analog common to reduce noise.
The USB-2537 has several analog common pins on both the 68-pin connector and the 40-pin connectors,
and the TB-7 has one analog common screw terminal.
You can also minimize the effect of noise by averaging readings (see "Averaging" below), or combining
both shielding and averaging.
Refer to "68-pin SCSI connector (P5)" on page 10, "40-pin header connector" on page 13, and "Fourchannel TC terminal block (TB7)" on page 16 for the locations of these analog common pins.
Make sure the USB-2537 is mounted on a flat surface.
Be careful to avoid loading down the digital outputs too heavily (>1 mA). Heavy load down causes
significant heat generation inside the unit and increase the CJC thermistor error.

Shielding
Use shielded TC wire with the shield connected to analog common to further reduce noise.
The USB-2537 has one analog common screw-terminal on TB7 and several analog common pins on theheaders. You can connect the shield of a shielded thermocouple to one of the analog commons. When thisconnection is made, leave the shield at the other end of the thermocouple unconnected.
Caution! Connecting the shield to common at both ends results in a ground loop.
Averaging
Certain acquisition programs apply averaging after several samples have been collected. Depending on thenature of the noise, averaging can reduce noise by the square root of the number of averaged samples.
Although averaging can be effective, it suffers from several drawbacks.
Noise in measurements only decreases as the square root of the number of measurements—reducing RMS
noise significantly may require many samples. Thus, averaging is suited to low-speed applications that can
provide many samples.
Only random noise is reduced or eliminated by averaging. Averaging does not reduce or eliminate periodic
signals.

Analog output
The USB-2537 has four 16-bit, 1 MHz analog output channels.
The channels have an output range of -10V to +10V. Each D/A output can continuously output a waveform at
up to 1 MHz. In addition, a program can asynchronously output a value to any of the D/A channels for nonwaveform applications, assuming that the D/A is not already being used in the waveform output mode.
When used to generate waveforms, you can clock the D/As in several different modes.
Internal output scan clock: The on-board programmable clock can generate updates ranging from 1 Hz to

1 MHz.


External output scan clock (XDPCR): A user-supplied external clock.
Internal input scan pacer clock: The internal ADC pacer clock can pace both the D/A and the analog

input.
External input scan pacer clock (XAPCR): The external ADC pacer clock can pace both the D/A and theanalog input.
24USB-2537 User's Guide

Functional Details

Example: Analog channel scanning of voltage inputs and streaming analog outputs
The example shown in Figure 12 adds four DACs and a 16-bit digital pattern output paced by the input scanclock to the example presented in Figure 8.

Figure 12. Analog channel scan of voltage inputs and streaming analog outputs example

This example updates all DACs and the 16-bits of digital I/O. These updates happen at the same time as theacquisition pacer clock—also called the input scan clock. All DACs and the 16-bits of pattern digital output are
updated at the beginning of each scan.
Due to the time it takes to shift the digital data out to the DACs, plus the actual settling time of the digital-toanalog conversion, the DACs actually take up to 4 µs after the start of scan to settle on the updated value.
The data for the DACs and pattern digital output comes from a PC-based buffer. The data is streamed across theUSB2 bus to the USB-2537.
In this example, the outputs are updated by the input scan clock, but you can also update the DACs and pattern
digital output with the output scan clock—either internally-generated or externally-applied. In this scenario, theacquisition input scans are not synchronized to the analog outputs or pattern digital outputs.

Digital I/O
Twenty-four TTL-level digital I/O lines are included in each USB-2537. You can program digital I/O in 8-bit
groups as either inputs or outputs and scan them in several modes (see "Digital input scanning" below). You canaccess input ports asynchronously from the PC at any time, including when a scanned acquisition is occurring.

Digital input scanning
Digital input ports can be read asynchronously before, during, or after an analog input scan. Digital input ports
can be part of the scan group and scanned along with analog input channels.
Two synchronous modes are supported when digital inputs are scanned along with analog inputs. Refer to"Example 4: Sampling digital inputs for every analog sample in a scan group" on page 23 for more information.
In both modes, adding digital input scans has no effect on the analog scan rate limitations. If no analog inputs
are being scanned, the digital inputs can sustain rates up to 4 MHz. Higher rates—up to 12 MHz—are possible
depending on the platform and the amount of data being transferred.

25

USB-2537 User's Guide

Functional Details

Digital outputs and pattern generation
Digital outputs can be updated asynchronously anytime before, during, or after an acquisition. You can use twoof the 8-bit ports to generate a digital pattern at up to 4 MHz. The USB-2537 supports digital pattern generation.
The digital pattern can be read from PC RAM.
Higher rates—up to 12 MHz—are possible depending on the platform and the amount of data being transferred.
Digital pattern generation is clocked using an internal clock. The on-board programmable clock generates
updates ranging from once every 1 second to 1 MHz, independent of any acquisition rate.

Triggering
Triggering can be the most critical aspect of a data acquisition application. The USB-2537 supports thefollowing trigger modes to accommodate certain measurement situations.

Hardware analog triggering
The USB-2537 uses true analog triggering in which the trigger level you program sets an analog DAC, which isthen compared in hardware to the analog input level on the selected channel. This guarantees an analog trigger
latency that is less than 1 µs.
You can select any analog channel as the trigger channel, but the selected channel must be the first channel inthe scan. You can program the trigger level, the rising or falling edge, and hysteresis.
A note on the hardware analog level trigger and comparator change state
When analog input voltage starts near the trigger level, and you are performing a rising or falling hardware
analog level trigger, the analog level comparator may have already tripped before the sweep was enabled. If thisis the case, the circuit waits for the comparator to change state. However, since the comparator has alreadychanged state, the circuit does not see the transition.
To resolve this problem, do the following:1.

Set the analog level trigger to the threshold you want.

2.

Apply an analog input signal that is more than 2.5% of the full-scale range away from the desired
threshold. This ensures that the comparator is in the proper state at the beginning of the acquisition.

3.

Bring the analog input signal toward the desired threshold. When the input signal is at the threshold(± some tolerance) the sweep will be triggered.

4.

Before re-arming the trigger, move the analog input signal to a level that is more than 2.5% of the full-scale
range away from the desired threshold.

For example, if you are using the ±2 V full-scale range (gain = 5), and you want to trigger at +1 V on the risingedge, you would set the analog input voltage to a start value that is less than +0.9 V (1 V – (2 V * 2 * 2.5%)).

Digital triggering
A separate digital trigger input line is provided (TTL TRG), allowing TTL-level triggering with latencies
guaranteed to be less than 1 µs. You can program both of the logic levels (1 or 0) and the rising or falling edge
for the discrete digital trigger input.

Software-based triggering
The three software-based trigger modes differ from hardware analog triggering and digital triggering because
the readings—analog, digital, or counter—are checked by the PC in order to detect the trigger event.
Analog triggering
You can select any analog channel in the scan as the trigger channel. You can program the trigger level, therising or falling edge, and hysteresis.

26

USB-2537 User's Guide

Functional Details

Pattern triggering
You can select any scanned digital input channel pattern to trigger an acquisition, including the ability to mask
or ignore specific bits.
Counter triggering
You can program triggering to occur when one of the counters meets or exceeds a set value, or is within a rangeof values. You can program any of the included counter channels as the trigger source.
Software-based triggering usually results in a long period of inactivity between the trigger condition being
detected and the data being acquired. However, the USB-2537 avoids this situation by using pre-trigger data.
When software-based-triggering is used, and the PC detects the trigger condition—which may be thousands ofreadings after the actual occurrence of the signal—the USB-2537 driver automatically looks back to thelocation in memory where the actual trigger-causing measurement occurred, and presents the acquired data thatbegins at the point where the trigger-causing measurement occurs. The maximum inactive period in this mode
equals one scan period.
Set pre-trigger > 0 when using counter as trigger source
When using a counter for a trigger source, you should use a pre-trigger with a value of at least 1. Since allcounters start at zero with the first scan, there is no valid reference in regard to rising or falling edge. Setting a
pre-trigger to 1 or more ensures that a valid reference value is present, and that the first trigger will be
legitimate.

Stop trigger modes
You can use any of the software trigger modes explained previously to stop an acquisition.
For example, you can program an acquisition to begin on one event—such as a voltage level—and then stop on
another event—such as a digital pattern.

Pre-triggering and post-triggering modes
The USB-2537 supports four modes of pre-triggering and post-triggering, providing a wide-variety of options toaccommodate any measurement requirement.
When using pre-trigger, you must use software-based triggering to initiate an acquisition.
No pre-trigger, post-trigger stop event
In this simple mode, data acquisition starts when the trigger is received, and the acquisition stops when the stoptrigger event is received.
Fixed pre-trigger with post-trigger stop event
In this mode, you set the number of pre-trigger readings to acquire. The acquisition continues until a stoptrigger event occurs.
No pre-trigger, infinite post-trigger
In this mode, no pre-trigger data is acquired. Instead, data is acquired beginning with the trigger event, and is
terminated when you issue a command to halt the acquisition.
Fixed pre-trigger with infinite post-trigger
You set the amount of pre-trigger data to acquire. Then, the system continues to acquire data until the programissues a command to halt acquisition.

Counter inputs
Four 32-bit counters are built into the USB-2537. Each counter accepts frequency inputs up to 20 MHz.
USB-2537 counter channels can be configured as standard counters or as multi-axis quadrature encoders.
The counters can concurrently monitor time periods, frequencies, pulses, and other event driven incremental
occurrences directly from pulse-generators, limit switches, proximity switches, and magnetic pick-ups.
27

USB-2537 User's Guide

Functional Details

Counter inputs can be read asynchronously under program control, or synchronously as part of an analog ordigital scan group.
When reading synchronously, all counters are set to zero at the start of an acquisition. When reading
asynchronously, counters may be cleared on each read, count up continually, or count until the 16 bit or 32 bit
limit has been reached. See the counter mode descriptions below.

Figure 13. Typical USB-2537 counter channel

Mapped channels
A mapped channel is one of four counter input signals that can get multiplexed into a counter module. The
mapped channel can participate with the counter's input signal by gating the counter, latching the counter, andso on. The four possible choices for the mapped channel are the four counter input signals (post-debounce).
A mapped channel can be used to:gate the counter
decrement the counterlatch the current count to the count register

Usually, all counter outputs are latched at the beginning of each scan within the acquisition. However, you can
use a second mapped channel to latch the counter output.

Counter modes
A counter can be asynchronously read with or without clear on read. The asynchronous read-signals strobe
when the lower 16-bits of the counter are read by software. The software can read the counter's high 16-bits
some time later after reading the lower 16-bits. The full 32-bit result reflects the timing of the first
asynchronous read strobe.
Totalize mode
The Totalize mode allows basic use of a 32-bit counter. While in this mode, the channel's input can only
increment the counter upward. When used as a 16-bit counter (counter low), one channel can be scanned at the
12 MHz rate. When used as a 32-bit counter (counter high), two sample times are used to return the full 32-bit
result. Therefore a 32-bit counter can only be sampled at a 6 MHz maximum rate. If you only want the upper 16
bits of a 32-bit counter, then you can acquire that upper word at the 12 MHz rate.
The counter counts up and does not clear on every new sample. However, it does clear at the start of a new scancommand.
The counter rolls over on the 16-bit (counter low) boundary, or on the 32-bit (counter high) boundary.
Clear on read mode
The counter counts up and is cleared after each read. By default, the counter counts up and only clears thecounter at the start of a new scan command. The final value of the counter —the value just before it was
cleared—is latched and returned to the USB-2537.
Stop at the top mode
The counter stops at the top of its count. The top of the count is FFFF hex (65,535) for the 16-bit mode, andFFFFFFFF hex (4,294,967,295) for the 32-bit mode.

28

USB-2537 User's Guide

Functional Details

32-bit or 16-bit
Sets the counter type to either 16-bits or 32-bits. The type of counter only matters if the counter is using the stopat the top mode—otherwise, this option is ignored.
Latch on map
Sets the signal on the mapped counter input to latch the count.
By default, the start of scan signal—a signal internal to the USB-2537 pulses once every scan period to indicate
the start of a scan group—latches the count, so the count is updated each time a scan is started.
Gating "on" mode
Sets the gating option to "on" for the mapped channel, enabling the mapped channel to gate the counter.
Any counter can be gated by the mapped channel. When the mapped channel is high, the counter is enabled.
When the mapped channel is low, the counter is disabled (but holds the count value). The mapped channel canbe any counter input channel other than the counter being gated.
Decrement "on" mode
Sets the counter decrement option to "on" for the mapped channel. The input channel for the counter increments
the counter, and you can use the mapped channel to decrement the counter.

Debounce modes
Each channel's output can be debounced with 16 programmable debounce times from 500 ns to 25.5 ms.
The debounce circuitry eliminates switch-induced transients typically associated with electro-mechanicaldevices including relays, proximity switches, and encoders.
There are two debounce modes, as well as a debounce bypass, as shown in Figure 14. In addition, the signal
from the buffer can be inverted before it enters the debounce circuitry. The inverter is used to make the input
rising-edge or falling-edge sensitive.
Edge selection is available with or without debounce. In this case the debounce time setting is ignored and the
input signal goes straight from the inverter or inverter bypass to the counter module.
There are 16 different debounce times. In either debounce mode, the debounce time selected determines how
fast the signal can change and still be recognized.
The two debounce modes are trigger after stable and trigger before stable. A discussion of the two modes
follows.

Figure 14. Debounce model block diagram29

USB-2537 User's Guide

Functional Details

Trigger after stable mode
In the trigger after stable mode, the output of the debounce module does not change state until a period ofstability has been achieved. This means that the input has an edge, and then must be stable for a period of timeequal to the debounce time.

Figure 15. Debounce module – trigger after stable mode

The following time periods (T1 through T5) pertain to Figure 15. In trigger after stable mode, the input signal
to the debounce module is required to have a period of stability after an incoming edge, in order for that edge tobe accepted (passed through to the counter module.) The debounce time for this example is equal to T2 and T5.







T1 – In the example above, the input signal goes high at the beginning of time period T1, but never stays
high for a period of time equal to the debounce time setting (equal to T2 for this example.)
T2 – At the end of time period T2, the input signal has transitioned high and stayed there for the required
amount of time—therefore the output transitions high. If the input signal does not stabilize in the high statelong enough, no transition would have appeared on the output and the entire disturbance on the input would
have been rejected.
T3 – During time period T3, the input signal remained steady. No change in output is seen.
T4 – During time period T4, the input signal has more disturbances and does not stabilize in any state longenough. No change in the output is seen.
T5 – At the end of time period T5, the input signal has transitioned low and stayed there for the required
amount of time—therefore the output goes low.

Trigger before stable mode
In the trigger before stable mode, the output of the debounce module immediately changes state, but will notchange state again until a period of stability has passed. For this reason the mode can be used to detect glitches.

Figure 16. Debounce module – Trigger before stable mode

The following time periods (T1 through T6) pertain to the above drawing.







T1 – In the illustrated example, the input signal is low for the debounce time (equal to T1); therefore when
the input edge arrives at the end of time period T1, it is accepted and the output (of the debounce module)
goes high. Note that a period of stability must precede the edge in order for the edge to be accepted.
T2 – During time period T2, the input signal is not stable for a length of time equal to T1 (the debounce
time setting for this example.) Therefore, the output stays "high" and does not change state during time
period T2.
T3 – During time period T3, the input signal is stable for a time period equal to T1, meeting the debounce
requirement. The output is held at the high state. This is the same state as the input.
T4 – At anytime during time period T4, the input can change state. When this happens, the output will alsochange state. At the end of time period T4, the input changes state, going low, and the output follows thisaction [by going low].
T5 – During time period T5, the input signal again has disturbances that cause the input to not meet thedebounce time requirement. The output does not change state.
T6 – After time period T6, the input signal has been stable for the debounce time and therefore any edge on
the input after time period T6 is immediately reflected in the output of the debounce module.
30

USB-2537 User's Guide

Functional Details

Debounce mode comparisons
Figure 17 shows how the two modes interpret the same input signal, which exhibits glitches. Notice that thetrigger before stable mode recognizes more glitches than the trigger after stable mode. Use the bypass option toachieve maximum glitch recognition.

Figure 17. Example of two debounce modes interpreting the same signal

Debounce times should be set according to the amount of instability expected in the input signal. Setting adebounce time that is too short may result in unwanted glitches clocking the counter. Setting a debounce time
too long may result in an input signal being rejected entirely. Some experimentation may be required to find theappropriate debounce time for a particular application.
To see the effects of different debounce time settings, simply view the analog waveform along with the counter
output. This can be done by connecting the source to an analog input.
Use trigger before stable mode when the input signal has groups of glitches and each group is to be counted asone. The trigger before stable mode recognizes and counts the first glitch within a group but rejects thesubsequent glitches within the group if the debounce time is set accordingly. The debounce time should be set
to encompass one entire group of glitches as shown in the following diagram.

Figure 18.Optimal debounce time for trigger before stable mode

Trigger after stable mode behaves more like a traditional debounce function: rejecting glitches and only passing
state transitions after a required period of stability. Trigger after stable mode is used with electro-mechanicaldevices like encoders and mechanical switches to reject switch bounce and disturbances due to a vibrating
encoder that is not otherwise moving. The debounce time should be set short enough to accept the desired input
pulse but longer than the period of the undesired disturbance as shown in Figure 19.

31

USB-2537 User's Guide

Functional Details

Figure 19. Optimal debounce time for trigger after stable mode

Encoder mode
Rotary shaft encoders are frequently used with CNC equipment, metal-working machines, packaging
equipment, elevators, valve control systems, and in a multitude of other applications in which rotary shafts are
involved.
The encoder mode allows the USB-2537 to make use of data from optical incremental quadrature encoders. In
encoder mode, the USB-2537 accepts single-ended inputs. When reading phase A, phase B, and index Z
signals, the USB-2537 provides positioning, direction, and velocity data.
The USB-2537 can receive input from up to two encoders.
The USB-2537 supports quadrature encoders with a 16-bit (counter low) or a 32-bit (counter high) counter,
20 MHz frequency, and X1, X2, and X4 count modes. With only phase A and phase B signals, two channels aresupported; with phase A, phase B, and index Z signals, 1 channel is supported. Each input can be debounced
from 500 ns to 25.5 ms (total of 16 selections) to eliminate extraneous noise or switch induced transients.
Encoder input signals must be within -5 V to +10 V and the switching threshold is TTL (1.3V).
Quadrature encoders generally have three outputs: A, B, and Z. The A and B signals are pulse trains driven by
an optical sensor inside the encoder. As the encoder shaft rotates, a laminated optical shield rotates inside theencoder. The shield has three concentric circular patterns of alternating opaque and transparent windows
through which an LED shines. There is one LED and one phototransistor for each of the concentric circularpatterns. One phototransistor produces the A signal, another phototransistor produces the B signal and the lastphototransistor produces the Z signal. The concentric pattern for A has 512 window pairs (or 1024, 4096, etc.)
When using a counter for a trigger source, use a pre-trigger with a value of at least 1. Since all counters start atzero with the initial scan, there is no valid reference in regard to rising or falling edge. Setting a pre-trigger to
1 or more ensures that a valid reference value is present, and that the first trigger is legitimate.

The concentric pattern for B has the same number of window pairs as A—except that the entire pattern isrotated by 1/4 of a window-pair. Thus the B signal is always 90 degrees out of phase from the A signal. The A
and B signals pulse 512 times (or 1024, 4096, etc.) per complete rotation of the encoder.
32

USB-2537 User's Guide

Functional Details

The concentric pattern for the Z signal has only one transparent window and therefore pulses only once percomplete rotation. Representative signals are shown in the following figure.
A
B

Z

Figure 20. Representation of quadrature encoder outputs: A, B, and Z

As the encoder rotates, the A (or B) signal indicates the distance the encoder has traveled. The frequency of A
(or B) indicates the velocity of rotation of the encoder. If the Z signal is used to zero a counter (that is clockedby A) then that counter gives the number of pulses the encoder has rotated from its reference. The Z signal is areference marker for the encoder. It should be noted that when the encoder is rotating clockwise (as viewed
from the back), A will lead B and when the encoder is rotating counterclockwise, A lags behind B. If thecounter direction control logic is such that the counter counts upward when A leads B and counts downward
when A lags B, then the counter gives direction control as well as distance from the reference.
Maximizing encoder accuracy
If there are 512 pulses on A, then the encoder position is accurate to within 360°/512.
You can get even greater accuracy by counting not only rising edges on A but also falling edges on A, giving
position accuracy to 360 degrees/1024.
You get maximum accuracy counting rising and falling edges on A and on B (since B also has 512 pulses.) This
gives a position accuracy of 360°/2048. These different modes are known as X1, X2, and X4.
Connecting the USB-2537 to an encoder
You can use up to two encoders with each USB-2537 in your acquisition system. Each A and B signal can bemade as a single-ended connection with respect to common ground.
Differential applications are not supported.
For single-ended applications:Connect signals A, B, and Z to the counter inputs on the USB-2537.
Connect each encoder ground to GND.

You can also connect external pull-up resistors to the USB-2537 counter input terminal blocks by placing apull-up resistor between any input channel and the encoder power supply. Choose a pull-up resistor value basedon the encoder's output drive capability and the input impedance of the USB-2537. Lower values of pull-up
resistors cause less distortion, but also cause the encoder's output driver to pull down with more current.
Connecting external pull-up resistors
For open-collector outputs, you can connect external pull-up resistors to the counter input terminal blocks. You
can place a pull-up resistor between any input channel and the provided +5 V power supply.
Choose a pull-up resistor value based on the encoder's output drive capability and the input impedance of theboard. Lower values of pull-up resistors cause less distortion but also cause the encoder's output driver to pull
down with more current.
Wiring to one encoder: Figure 21 shows the connections for one encoder to a module.

The following figure illustrates connections for one encoder to a 68-pin SCSI connector on a USB-2537. The"A" signal must be connected to an even-numbered channel and the associated "B" signal must be connected to
the next [higher] odd-numbered channel. For example, if "A" were connected to CTR0, "B" would be connected
to CTR1.

33

USB-2537 User's Guide

Functional Details+5 VDC, pin 19
To ground (of external power source)

Ground (to Digital Common pin 35, 36, 40)
Counter 0 (CNT0, pin 5) – To Encoder “A”
Counter 1 (CNT1, pin 39) – To Encoder “B”
Counter 2 (CNT2, pin 4) – To Encoder “Z”

Figure 21. Encoder connections to pins on the SCSI connector** Connections can instead be made to the associated screw-terminals of a connected TB-100 terminal.
The "A" signal must be connected to an even-numbered channel and the associated "B" signal must beconnected to the next higher odd-numbered channel. For example, if "A" were connected to counter 0, then "B"
would be connected to counter 1.
If the encoder stops rotating, but is vibrating (due to it being mounted to a machine), you can use the debounce
feature to eliminate false edges. Choose an appropriate debounce time and apply it to each encoder channel.
Refer to Debounce modes on page 29 for additional information regarding debounce times.
You can get the relative position and velocity from the encoder. However, during an acquisition, you cannot getdata that is relative to the Z-position until the encoder locates the Z-reference.
Note that the number of Z-reference crossings can be tabulated. If the encoder was turning in only one direction,then the Z-reference crossings equal the number of complete revolutions. This means that the data streaming to
the PC is relative position, period = 1/velocity, and revolutions.
A typical acquisition might take six readings off of the USB-2537 as illustrated below. The user determines thescan rate and the number of scans to take.

Figure 22. USB-2537 acquisition of six readings per scan

Digital channels do not take up analog channel scan time.
In general, the output of each channel’s counter is latched at the beginning of each scan period (called the startof-scan.) Every time the USB-2537 receives a start-of-scan signal, the counter values are latched and areavailable to the USB-2537.
The USB-2537 clears all counter channels at the beginning of the acquisition. This means that the values
returned during scan period 1 are always zero. The values returned during scan period 2 reflect what happened
during scan period 1.
The scan period defines the timing resolution for the USB-2537. If you need a higher timing resolution, shorten
the scan period.

34

USB-2537 User's Guide

Functional Details

Wiring for two encoders: Figure 23 shows the single-ended connections for two encoders. Differential

connections do not apply.

Figure 23. Two encoders connected to pins on the SCSI connector** Connections can instead be made to the associated screw-terminals of a connected TB-100 connector.
Each signal (A, B) can be connected as a single-ended connection with respect to the common digital ground(GND). Both encoders can draw their power from the +5 V power output (pin 19) on the 68-pin SCSI
connector.
Connect each encoder’s power input to +5 V power. Connect the return to digital common (GND) on the sameconnector. Make sure that the current output spec is not violated.
With the encoders connected in this manner, there is no relative positioning information available on encoder #1
or #2 since there is no Z signal connection for either. Therefore only distance traveled and velocity can bemeasured for each encoder.

Timer outputs
Two 16-bit timer outputs are built into the USB-2537. Each timer is capable of generating a different squarewave with a programmable frequency in the range of 16 Hz to 1 MHz.

Figure 24. Typical USB-2537 timer channel

Example: Timer outputs
Timer outputs are programmable square waves. The period of the square wave can be as short as 1 µs or as longas 65535 µs. Refer to the table below for examples of timer output frequencies.
Timer output frequency examples
DivisorTimer output frequency

1

1 MHz

100

10 kHz

1000

1 kHz

10000

100 Hz65535

15.259 Hz

35

USB-2537 User's Guide

Functional Details

The two timer outputs can generate different square waves. The timer outputs can be updated asynchronously at
any time.

Using detection setpoints for output control
What are detection setpoints?
With the USB-2537's setpoint configuration feature, you can configure up to 16 detection setpoints associatedwith channels in a scan group. Each setpoint can update the following, allowing for real-time control based on
acquisition data:

FIRSTPORTC digital output port with a data byte and mask byte
analog outputs (DACs)
timers

Setpoint configuration overview
You can program each detection setpoint as one of the following:Single point referenced – Above, below, or equal to the defined setpoint.
Window (dual point) referenced – Inside or outside the window.
Window (dual point) referenced, hysteresis mode – Outside the window high forces one output (designatedOutput 2; outside the window low-forces another output, designated as Output 1).

A digital detect signal is used to indicate when a signal condition is True or False—for example, whether or not
the signal has met the defined criteria. The detect signals can be part of the scan group and can be measured as
any other input channel, thus allowing real time data analysis during an acquisition.
The detection module looks at the 16-bit data being returned on a channel and generates another signal for eachchannel with a setpoint applied (Detect1 for Channel 1, Detect2 for Channel 2, and so on). These signals serveas data markers for each channel's data. It does not matter whether that data is volts, counts, or timing.
A channel's detect signal shows a rising edge and is True (1) when the channel's data meets the setpoint criteria.
The detect signal shows a falling edge and is False (0) when the channel's data does not meet the setpoint
criteria. The True and False states for each setpoint criteria are explained in the "Using the setpoint status
register" section on page 38.
Criteria – input signal is equal to X

Action - driven by condition

Compare X to:

Update conditions:True only: If True, then output value 1
 If False, then perform no action
True and False: If True, then output value 1
 If False, then output value 2
True only If True, then output value 1
 If False, then perform no action
True and False If True, then output value 1
 If False, then output value 2

Setpoint definition (choose one)
Equal to A (X = A)
Below A (X < A)
 Above B (X > B)

Limit A or Limit BWindow* (nonhysteresis mode)Inside (B < X < A)
Outside: B > X; or, X > A

36

USB-2537 User's Guide

Functional Details

Criteria – input signal is equal to X

Window*(hysteresis mode)Above A (X > A)
Below (B X < B) (Bothconditions are checked whenin hysteresis mode

Action - driven by condition
Hysteresis mode (forced update) If X > A is True, then output value 2 until X < B is True, thenoutput value 1.
 If X < B is True, then output value 1 until X > A is True, thenoutput value 2.
This is saying:(a) If the input signal is outside the window high, then output
value 2 until the signal goes outside the window low, and(b) if the signal is outside the window low, then output value 1
until the signal goes outside the window high. There is nochange to the detect signal while within the window.

The detect signal has the timing resolution of the scan period as seen in the diagram below. The detect signal
can change no faster than the scan frequency (1/scan period.)

Figure 25. Example diagram of detection signals for channels 1, 2, and 3

Each channel in the scan group can have one detection setpoint. There can be no more than 16 total setpoints
total applied to channels within a scan group.
Detection setpoints act on 16-bit data only. Since the USB-2537 has 32-bit counters, data is returned 16-bits at atime. The lower word, the higher word, or both lower and higher words can be part of the scan group. Eachcounter input channel can have one detection setpoint for the counter's lower 16-bit value and one detection
setpoint for the counter's higher 16-bit value.

Setpoint configuration
You program all setpoints as part of the pre-acquisition setup, similar to setting up an external trigger. Since
each setpoint acts on 16-bit data, each has two 16-bit compare values: a high limit (limit A) and a low limit(limit B). These limits define the setpoint window.
There are several possible conditions (criteria) and effectively three update modes, as explained in the following
configuration summary.
Set high limit
You can set the 16-bit high limit (limit A) when configuring the USB-2537 through software.
Set low limit
You can set the 16-bit low limit (limit B) when configuring the USB-2537 through software.
Set criteriaInside window: Signal is below 16-bit high limit and above 16-bit low limit.
Outside window: Signal is above 16-bit high limit, or below 16-bit low limit.
37

USB-2537 User's Guide







Functional Details

Greater than value: Signal is above 16-bit low limit, so 16-bit high limit is not used.
Less than value: Signal is below 16-bit high limit, so 16-bit low limit is not used.
Equal to value: Signal is equal to 16-bit high limit, and limit B is not used.
The equal to mode is intended for use when the counter or digital input channels are the source channel.
You should only use the equal to16-bit high limit (limit A) mode with counter or digital input channels as
the channel source. If you want similar functionality for analog channels, then use the inside window mode
Hysteresis mode: Outside the window, high forces output 2 until an outside the window low condition
exists, then output 1 is forced. Output 1 continues until an outside the window high condition exists. The
cycle repeats as long as the acquisition is running in hysteresis mode.

Set output channel





None
Update FIRSTPORTC
Update DAC
Update timerx

Update modes

Update on True only
Update on True and False

Set values for output


16-bit DAC value, FIRSTPORTC* value, or timer value when input meets criteria.
16-bit DAC value, FIRSTPORTC* value, or timer value when does not meet criteria.
* By default, FIRSTPORTC comes up as a digital input. You may want to initialize FIRSTPORTC to a
known state before running the input scan to detect the setpoints.

When using setpoints with triggers other than immediate, hardware analog, or TLL, the setpoint criteria
evaluation begins immediately upon arming the acquisition.

Using the setpoint status register
You can use the setpoint status register to check the current state of the 16 possible setpoints. In the register,Setpoint 0 is the least-significant bit and Setpoint 15 is the most-significant bit. Each setpoint is assigned avalue of 0 or 1.


A value of 0 indicates that the setpoint criteria is not met—in other words, the condition is False.
A value of 1 indicates that the criteria has been met—in other words, the condition is True.

In the following example, the criteria for setpoints 0, 1, and 4 is satisfied (True), but the criteria for the other 13
setpoints has not been met.
Setpoint #True (1)False (0)

15
0

14
0

13
0

12
0

11
0

10
0

9
0

8
0

7
0

6
0

5
0

<<< Most significant bit

4
1

3
0

1
1

0
1

Least significant bit >>>From the above table we have 10011 binary, or 19 decimal, derived as follows:




2
0

Setpoint 0, having a True state, shows 1, giving us decimal 1.
Setpoint 1, having a True state, shows 1, giving us decimal 2.
Setpoint 4, having a True state, shows 1, giving us decimal 16.

For proper operation, the setpoint status register must be the last channel in the scan list.

38

USB-2537 User's Guide

Functional Details

Examples of control outputs
Detecting on analog input, DAC, and FIRSTPORTC updates
Update mode: Update on True and False
Criteria: Channel 5 example: below limit; channel 4 example: inside window
In this example, channel 5 is programmed with reference to one setpoint (limit A), defining a low limit.
Channel 4 is programmed with reference to two setpoints (limit A and limit B) which define a window for thatchannel.
ChannelCondition

State of detectsignalAction5

Below limit A (forchannel 5)

True

When channel 5 analog input voltage is below the limit
A, update DAC1 with output value 0.0 V.
When the above stated condition is false, update DAC1
with the Output Value of minus 1.0 V.
When Channel 4's analog input voltage is within thewindow, update FIRSTPORTC with 70h.
When the above stated condition is False (channel 4
analog input voltage is outside the window), update
FIRSTPORTC with 30h.

False
4

Within window (between
limit A and limit B) forchannel 4

True
False

Figure 26. Analog inputs with setpoints update on True and False

39USB-2537 User's Guide

Functional Details

In the channel 5 example, the setpoint placed on analog Channel 5 updated DAC1 with 0.0 V. The update
occurred when channel 5's input was less than the setpoint (limit A). When the value of channel 5's input wasabove setpoint limit A, the condition of <A was false and DAC1 was then updated with minus1.0V.
You can program control outputs programmed on each setpoint, and use the detection for channel 4 to update
the FIRSTPORTC digital output port with one value (70 h in the example) when the analog input voltage iswithin the shaded region and a different value when the analog input voltage is outside the shaded region (30 hin the example).
Detection on an analog input, timer output updates
Update Mode: Update on True and False
Criteria Used: Inside window
The figure below shows how a setpoint can be used to update a timer output. Channel 3 is an analog input
channel. A setpoint is applied using update on True and False, with a criteria of inside-the-window, where thesignal value is inside the window when simultaneously less than Limit A but greater than Limit B.
Whenever the channel 3 analog input voltage is inside the setpoint window (condition True), Timer0 is updatedwith one value; and whenever the channel 3 analog input voltage is outside the setpoint window (condition
False) timer0 will be updated with a second output value.

Figure 27. Timer output update on True and False

Using the hysteresis function
Update mode: N/A, the hysteresis option has a forced update built into the function
Criteria used: Window criteria for above and below the set limits
The figure below shows analog input Channel 3 with a setpoint which defines two 16-bit limits, Limit A (High)and Limit B (Low). These are being applied in the hysteresis mode and DAC channel 0 is updated accordingly.
In this example, Channel 3's analog input voltage is being used to update DAC0 as follows:When outside the window, low (below limit B) DAC0 is updated with 3.0 V. This update remains in effectuntil the analog input voltage goes above Limit A.
When outside the window, high (above limit A), DAC0 is updated with 7.0 V. This update remains ineffect until the analog input signal falls below limit B. At that time we are again outside the limit "low" andthe update process repeats itself.

Hysteresis mode can also be done with FIRSTPORTC digital output port, or a timer output, instead of a DAC.

40

USB-2537 User's Guide

Functional Details

Figure 28. Channel 3 in hysteresis mode

Using multiple inputs to control one DAC output
Update mode: Rising edge, for each of two channels
Criteria used: Inside window, for each of two channels
The figure below shows how multiple inputs can update one output. In the following figure, the DAC2 analog
output is being updated. Analog input Channel 3 has an inside-the-window setpoint applied. Whenever Channel
3's input goes inside the programmed window, DAC2 will be updated with 3.0V.
Analog input Channel 7 also has an inside-the-window setpoint applied. Whenever channel 7's input goes inside
the programmed window, DAC2 is updated with - 7.0V.

Figure 29. Using two criteria to control an output*

The update on True only mode was selected, and therefore the updates for DAC2 only occur when the criteria ismet. However, in the above figure we see that there are two setpoints acting on one DAC. We can also see thatthe two criteria can be met simultaneously. When both criteria are True at the same time, the DAC2 voltage isassociated with the criteria that has been most recently met.

41

USB-2537 User's Guide

Functional Details

Detecting setpoints on a totalizing counterIn the following figure, Channel 1 is a counter in totalize mode. Two setpoints define a point of change for
Detect 1 as the counter counts upward. The detect output is high when inside the window (greater than Limit B(the low limit) but less than Limit A (the high limit).
In this case, the Channel 1 setpoint is defined for the 16 lower bits of channel 1's 32-bit value. The
FIRSTPORTC digital output port could be updated on a True condition (the rising edge of the detection signal).
You can also update one of the DAC output channels or timer outputs with a value.

At this point you can update FIRSTPORTC or DACs

Figure 30. Channel 1 in totalizing counter mode, inside the window setpoint

Detection setpoint details
Controlling analog, digital, and timer outputs
You can program each setpoint with an 8-bit digital output byte and corresponding 8-bit mask byte. When the
setpoint criteria is met, the FIRSTPORTC digital output port can be updated with the given byte and mask. You
can also program each setpoint with:a 16-bit DAC update value, and any one of the four DAC outputs can be updated in real timea timer update value

In hysteresis mode, each setpoint has two forced update values. Each update value can drive one DAC, one
timer, or the FIRSTPORTC digital output port. In hysteresis mode, the outputs do not change when the input
values are inside the window. There is one update value that gets applied when the input values are less than thewindow and a different update value that gets applied when the input values are greater than the window.
Update on True and False uses two update values. The update values can drive DACs, FIRSTPORTC, or timer
outputs.
FIRSTPORTC digital outputs can be updated immediately upon setpoint detection. This is not the case foranalog outputs, as these incur another 3 µs delay. This is due to the shifting of the digital data out to the D/Aconverter which takes 1 µs, plus the actual conversion time of the D/A converter, i.e., another 2µs (worst case).
Going back to the above example, if the setpoint for analog input Channel 2 required a DAC update it would
occur 5µs after the ADC conversion for Channel 2, or 6µs after the start of the scan.
When using setpoints to control any of the DAC outputs, increased latencies may occur if attempting to stream
data to DACs or pattern digital output at the same time. The increased latency can be as long as the period of
the DAC pacer clock. For these reasons, avoid streaming outputs on any DAC or pattern digital output whenusing setpoints to control DACs.

42

USB-2537 User's Guide

Functional Details

FIRSTPORTC, DAC, or timer update latency
Setpoints allow analog outputs, DACs, timers, or FIRSTPORTC digital outputs to update very quickly. Exactly
how fast an output can update is determined by these factors:scan ratesynchronous sampling mode
type of output to be updated

For example, you set an acquisition to have a scan rate of 100 kHz, which means each scan period is 10 µs.
Within the scan period you sample six analog input channels. These are shown in the following figure as
channels 1 through 6. The ADC conversion occurs at the beginning of each channel's 1 µs time block.

Figure 31. Example of FIRSTPORTC or DAC latency

By applying a setpoint on analog input channel 2, that setpoint gets evaluated every 10 µs with respect to thesampled data for channel 2.
Due to the pipelined architecture of the analog-to-digital converter system, the setpoint cannot be evaluateduntil 2 µs after the ADC conversion. In the example above, the FIRSTPORTC digital output port can be
updated no sooner than 2 µs after channel 2 has been sampled, or 3 µs after the start of the scan. This 2 µs delay
is due to the pipelined ADC architecture. The setpoint is evaluated 2 µs after the ADC conversion and then
FIRSTPORTC can be updated immediately.
The detection circuit works on data that is put into the acquisition stream at the scan rate. This data is acquired
according to the pre-acquisition setup (scan group, scan period, etc.) and returned to the PC. Counters arelatched into the acquisition stream at the beginning of every scan. The actual counters may be counting much
faster than the scan rate, and therefore only every 10 th, 100th, or nth count shows up in the acquisition data.
As a result, you can set a small detection window on a totalizing counter channel and have the detection setpoint"stepped over" since the scan period was too long. Even though the counter value stepped into and out of thedetection window, the actual values going back to the PC may not. This is true no matter what mode the counterchannel is in.
When setting a detection window, keep a scan period in mind. This applies to analog inputs and counter inputs.
Quickly changing analog input voltages can step over a setpoint window if not sampled often enough.
There are three possible solutions for overcoming this problem:

Shorten the scan period to give more timing resolution on the counter values or analog values.
Widen the setpoint window by increasing limit A and/or lowering limit B.
A combination of both solutions (1 and 2) could be made.

43

USB-2537 User's Guide

Functional Details

Mechanical drawing

Figure 32. Circuit board dimensions

44

Chapter 4

Calibrating the USB-2537
Board ranges are calibrated at the factory using a digital NIST traceable calibration method in which acorrection factor for each range is stored on the unit at the time of calibration.
Two calibration tables are stored on the board in EPROM — one table contains the factory calibration, and theother is available for field calibration. You can adjust the AI calibration while the board is installed in theacquisition system without destroying the factory calibration supplied with the board.
You can perform field calibration automatically in seconds with InstaCal. No external hardware or instruments
are required. Field calibration derives its traceability through an on-board reference which has a stability of
0.005% per year.
Calibrate the board after it has fully warmed up; the recommended warm-up time is 30 minutes. For best results,
calibrate the board immediately before making critical measurements. The high resolution analog components
on the board are somewhat sensitive to temperature. Pre-measurement calibration ensures that your board isoperating at optimum calibration values.
The recommended calibration interval is one year.

45

Chapter 5

Specifications
All specifications are subject to change without notice.
Typical for 25°C unless otherwise specified.
Specifications in italic text are guaranteed by design.

Analog input
Table 1. Analog input specifications
Parameter

Specification

A/D converter type
Resolution
Number of channels
Input ranges (SW programmable)
Sample rate
Nonlinearity (integral)
Nonlinearity (differential)
A/D pacing
Trigger sources and modes
Acquisition data buffer
Configuration memory

Successive approximation
16-bit64 single-ended/32 differential, software-selectable
Bipolar: ±10 V, ±5 V, ±2 V, ±1 V , ±0.5 V, ±0.2 V, ±0.1 V
1 MHz max
±2 LSB max±1 LSB max
Onboard input scan clock, external source (XAPCR)
See Table 8
1 MSample
Programmable I/O
Range ±10 V, ±5 V, ±2 V, ±1 V, ±0.5 V: 10.5 V max
Range ±0.2 V, ±0.1 V: 2.1 V max

Maximum usable input voltage+ common mode voltage (CMV + Vin)
Signal to noise and distortion
Total harmonic distortion
Calibration

72 dB typ for ±10 V range, 1 kHz fundamental–80 dB typ for ±10 V range, 1 kHz fundamental
Auto-calibration, calibration factors for each range stored onboard in
non-volatile RAM–70 dB typ DC to 1 kHz
40 pA typ (0 °C to 35°C)–75 dB typ DC to 60 Hz; -65 dB typ @ 10 kHz
10 MΩ single-ended, 20 MΩ differential±30 V

CMRR @ 60 Hz
Bias current
Crosstalk
Input impedance
Absolute maximum input voltage

Accuracy
Table 2. Analog input accuracy specifications
Voltage range(Note 1)

Accuracy±(% of reading + % range)
23 °C ±10 °C, 1 year

Temperature coefficient±(ppm of reading + ppm range)/°C

Noise (cts RMS)
(Note 2)–10 V to 10 V
–5 V to 5 V–2 V to 2 V–1 V to 1 V–500 mV to 500 mV–200 mV to 200 mV–100 mV to 100 mV

0.031% + 0.008%
0.031% + 0.009%
0.031% + 0.010%
0.031% + 0.02%
0.031% + 0.04%
0.036% + 0.075%
0.042% + 0.15%

14 + 8
14 + 914 +1014 + 12
14 +18
14 +12
14 +18

2.0
3.0
2.0
3.5
5.5
8.0
14.0

Note 1:
Note 2:

Specifications assume differential input single-channel scan, 1 MHz scan rate, unfiltered, CMV=0.0 V,
30 minute warm-up, exclusive of noise, range is +FS to –FS.
Noise reflects 10,000 samples at 1 MHz, typical, differential short.

46

USB-2537 User's Guide

Specifications

Thermocouples
Table 3. TC types and accuracy (Note 3)
TC typeTemperature range (°C)

Accuracy (±°C)

Noise typical (±°C)

J
K
T
E
R
S
N
B

–200 to + 760–200 to + 1200
–200 to + 400–270 to + 650–50 to + 1768
–50 to + 1768
–270 to + 1300
+300 to + 1400

1.7
1.8
1.8
1.7
4.8
4.7
2.7
3.0

0.2
0.2
0.2
0.2
1.5
1.5
0.3
1.0

Note 3:

Assumes 16,384 oversampling applied, CMV = 0.0 V, 60 minute warm-up, still environment, and 25 °C
ambient temperature; excludes thermocouple error; TCin = 0 °C for all types except B (1000 °C), PS9V1AEPS-2500 power supply for external power.

Analog outputs
Analog output channels can be updated synchronously relative to scanned inputs, and clocked from either aninternal onboard clock, or an external clock source. Analog outputs can also be updated asynchronously,
independent of any other scanning system.
Table 4. Analog output specifications
Parameter

Specification

Channels
Resolution
Data buffer
Output voltage range
Output current

4
16-bits
PC-based memory±10 V±1 mA; sourcing more current (1 mA to 10 mA) may require a PS-9V1AEPS-2500 power
supply option±0.0045 V max< 10 mV when updated< 12 mV typ at major carry±0.01%
DC
1 MHz max, resolution 20.83 ns
2 µs to rated accuracy
Four programmable sources:
 Onboard output scan clock, independent of scanning input clock Onboard input scan clock External output scan clock (XDPCR), independent of external input scan clock (XAPCR) External input scan clock (XAPCR)
Start of input scan

Offset error
Digital feed-through
DAC analog glitch
Gain error
Coupling
Update rate
Settling time
Pacer sources

Trigger sources47

USB-2537 User's Guide

Specifications

Digital input/output
Table 5. Digital I/O specifications
Parameter

Specification

Number of I/O
Configuration
Input scanning modes

24
Three 8-bit ports; each port is programmable as input or output
Two programmable modes:
 Asynchronous, under program control at any time relative to input scanning Synchronous with input scanning220 Ω series resistors, 20 pF to common
Holds the logic value to 0 or 1 when there is no external driver±15 kV ESD clamp diodes parallel+2.0 V to +5.0 V
0 to 0.8 V>2.0 V<0.8 V
Output 1.0 mA per pin, sourcing more current may require a PS-9V1AEPS-2500
power supply option
Onboard clock, external input scan clock (XAPCR)
Four programmable sources:
 Onboard output scan clock, independent of input scan clock Onboard input scan clock External output scan clock (XDPCR), independent of external input scan clock(XAPCR) External input scan clock (XAPCR)
See Table 8

Input characteristics
Logic keeper circuit
Input protection
Input highInput low
Output highOutput low
Output current
Digital input pacing
Digital output pacing

Digital input trigger sources andmodes
Digital output trigger sources
Sampling/update rate
Pattern generation output

Start of input scan
4 MHz max (rates up to 12 MHz are sustainable on some platforms)
Two of the 8-bit ports can be configured for 16-bit pattern generation. The pattern
can also be updated synchronously with an acquisition at up to 4 MHz.

Counters
Counter inputs can be scanned based on an internal programmable timer or an external clock source.
Table 6. Counter specifications
Parameter

Specification

Channels
Resolution
Input frequency
Input signal range
Input characteristics

4 independent32-bit20 MHz max–5 V to 10 V

Trigger level
Minimum pulse widthDe-bounce times
Time-base accuracyCounter read pacer
Trigger sources and modes
Programmable mode
Counter mode options

10 k pull-up, ±15 kV ESD protection
TTL
25 ns high, 25 ns low
16 selections from 500 ns to 25.5 ms, positive or negative edge sensitive, glitch
detect mode or de-bounce mode
50 ppm (0 °C to 50 °C)
Onboard input scan clock, external input scan clock (XAPCR)
See Table 8
Counter
Totalize, clear on read, rollover, stop at all Fs, 16-bit or 32-bit, any other channel
can gate the counter48

USB-2537 User's Guide

Specifications

Input sequencer
Analog, digital, and counter inputs can be scanned based on either an internal programmable timer or an
external clock source.
Table 7. Input sequencer specifications
Parameter

Specification

Input scan clock sources(Note 4)

Internal: Analog channels from 1 µs to 1 sec in 20.83 ns steps
 Digital channels and counters from 250 ns to 1 sec in 20.83 ns steps
External, TTL level input (XAPCR): Analog channels down to 1 µs min Digital channels and counters down to 250 ns min
Programmable channels (random order), programmable gain
512 locations
Analog: 1 MHz max
Digital: 4 MHz if no analog channels are enabled, 1 MHz with analog channels
enabledAnalog: 1MHz
Digital: 4 MHz if no analog channels are enabled, 1 MHz with analog channels
enabled
Logical zero: 0 V to 0.8 V
Logical one: 2.4 V to 5.0 V
50 ns high, 50 ns low

Programmable parameters per scan
Depth
Onboard channel to channel scanrate
External input scan clock (XAPCR)
maximum rate
Clock signal range
Minimum pulse width
Note 4:The maximum scan clock rate is the inverse of the minimum scan period. The minimum scan period is equal to1 µs times the number of analog channels.
If a scan contains only digital channels, the minimum scan period is 250 ns. Some platforms can sustain scanrates up to 83.33 ns for digital-only scans.

Trigger sources and modes
Table 8. Trigger sources and modes
Parameter

Specification

Input scan trigger sourcesSingle channel analog hardware trigger
Single channel analog software trigger
 External-single channel digital trigger (TTL TRG input)
 Digital Pattern Trigger Counter/Totalizer Trigger
 Single channel analog hardware trigger:
The first analog input channel in the scan is the analog trigger channel
Input signal range: –10 V to +10 V max
Trigger level: Programmable (12-bit resolution)
Latency: 350 ns typ
Accuracy: ±0.5% of reading, ±2 mV offset max
Noise: 2 mV RMS typ Single channel analog software trigger:
The first analog input channel in the scan is the analog trigger channel
Input signal range: Anywhere within range of the trigger channel
Trigger level: Programmable (16-bit resolution)
Latency: One scan period max
 External-single channel digital trigger (TTL trigger input):
Input signal range: –15 V to +15 V max
Trigger level: TTL level sensitive
Minimum pulse width: 50 ns high, 50 ns low
Latency: One scan period max
Input scan triggering modes49

USB-2537 User's Guide

Specifications

Parameter

Specification
Digital Pattern Triggering
8-bit or 16-bit pattern triggering on any of the digital ports. Programmable fortrigger on equal, not equal, above, or below a value. Individual bits can bemasked for "don’t care" condition.
Latency: One scan period max
 Counter/Totalizer Triggering
Counter/totalizer inputs can trigger an acquisition. User can select to trigger on afrequency or on total counts that are equal, not equal, above, or below a value, orwithin/outside of a window rising/falling edge.
Latency: One scan period max
Frequency/pulse generators
Table 9. Frequency/pulse generator specifications
Parameter

Specification

Channels
Output waveform
Output rate
High-level output voltage
Low-level output voltage

2 × 16-bit
Square wave
1 MHz base rate divided by 1 to 65,535 (programmable)
2.0 V min @ –1.0 mA, 2.9 V min @ –400 µA
0.4 V max @ 400 µA

Power consumption
Table 10. Power consumption specifications (Note 5)
Parameter

Specification

Power consumption (per board)

3400 mW

External power
Table 11. External power specifications (Note 5)
Parameter

Specification

Connector
Power range

Switchcraft # RAPC-712
6 VDC to 16 VDC; use when the USB port supplies insufficient power, or when an
independent power supply is desired.
20 V for 10 seconds, max

Over-voltage
Note 5:An optional power supply (MCC p/n PS-9V1AEPS-2500) is required if the USB port cannot supply adequate
power. USB 2.0 ports are required by USB 2.0 standards to supply 2500 mW (nominal at 5 V, 500 mA).

USB specifications
Table 12. USB specifications
Parameter

Specification

USB-device type

USB 2.0 high-speed mode (480 Mbps), recommended
USB 1.1 full-speed mode (12 Mbps)
USB 2.0 (recommended) or USB 1.1

Device compatibility

50

USB-2537 User's Guide

Specifications

Environmental
Table 13. Environmental specifications
Parameter

Specification

Operating temperature range
Storage temperature range
Relative humidity–30 °C to +70 °C–40 °C to +80 °C
0 to 95% non-condensing

Mechanical
Table 14. Mechanical specifications
Parameter

Specification

Vibration
Dimensions (W × D)
WeightMIL STD 810E cat 1 and 10
152.4 × 150.62 mm (6.0 × 5.93 in.)147 g (0.32 lb)

Signal I/O connectors
Table 15. Signal connector specifications
Parameter

Specification

Connector type68-pin standard "SCSI TYPE III" female connector (P5)40-pin headers (J5, J6, J7, J8), AMP# 2-103328-0
4-channel TC screw-terminal block (TB7); Phoenix # MPT 0.5/9-2.54

Temperature measurement
connector
Compatible cables(SCSI connector)
Compatible cables(header connectors)
Compatible accessory products(SCSI connector)
Compatible accessory products(header connectors)

CA-68-3R — 68-pin ribbon cable; 3 feet
CA-68-3S — 68-pin shielded round cable; 3 feet
CA-68-6S — 68-pin shielded round cable; 6 feet
C40FF-#
TB-100; termination board with screw terminals
RM-TB-100; 19-inch rack mount kit for the TB-100
CIO-MINI40


51

USB-2537 User's Guide

Specifications

68-pin SCSI connector (P5)
Table 16. Connector P5 single-ended pinout
Pin
68
67
66
65
64
63
62
61
60
59
58
57
56
55
54
53
52
51
50
49
48
47
46
45
44
43
42
41
40
39
38
37
36
35

Function
ACH0
AGND
ACH9
ACH2
AGND
ACH11
SGND (low level sense - not for general use)
ACH12
ACH5
AGND
ACH14
ACH7
XDAC3
XDAC2
NEGREF (reserved for self-calibration)
GND
A1
A3
A5
A7
B1
B3
B5
B7
C1
C3
C5
C7
GND
CNT1
CNT3
TMR1
GND
GND

Pin
34
33
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

52

Function
ACH8
ACH1
AGND
ACH10
ACH3
AGND
ACH4
AGND
ACH13
ACH6
AGND
ACH15
XDAC0
XDAC1
POSREF (reserved for self-calibration)+5 V (see Note 6)
A0
A2
A4
A6
B0
B2
B4
B6
C0
C2
C4
C6
TTL TRG
CNT0
CNT2
TMR0
XAPCR (input scan clock)
XDPCR (output scan clock)USB-2537 User's Guide

Specifications

Table 17. Connector P5 differential pinout
Pin
68
67
66
65
64
63
62
61
60
59
58
57
56
55
54
53
52
51
50
49
48
47
46
45
44
43
42
41
40
39
38
37
36
35

Note 6:Function
ACH0 HIAGND
ACH1 LO
ACH2 HIAGND
ACH3 LO
SGND (not for general use)
ACH4 LO
ACH5 HIAGND
ACH6 LO
ACH7 HIXDAC3
XDAC2
NEGREF (reserved for self-calibration)
GND
A1
A3
A5
A7
B1
B3
B5
B7
C1
C3
C5
C7
GND
CNT1
CNT3
TMR1
GND
GND

Pin
34
33
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

Function
ACH0 LO
ACH1 HIAGND
ACH2 LO
ACH3 HIAGND
ACH4 HIAGND
ACH5 LO
ACH6 HIAGND
ACH7 LOXDAC0
XDAC1
POSREF (reserved for self-calibration)+5 V (see Note 6)
A0
A2
A4
A6
B0
B2
B4
B6
C0
C2
C4
C6
TTL TRG
CNT0
CNT2
TMR0
XAPCR (input scan clock)
XDPCR (output scan clock)

5 V output, ±20% tolerance, 2mA USB powered, 10mA using external power.

53

USB-2537 User's Guide

Specifications

40-pin header connectors

This edge of the header is closest to the center of theboard. Pins 2 and 40 are labeled on the board silkscreen.

J5
Table 18. Connector J5 single-ended pinout
Pin
1
3
5
7
9
11
13
15
17
19
21
23
25
27
29
31
33
35
37
39

Function
ACH27
ACH26
AGND
ACH3
ACH2
ACH17
ACH16
ACH1
ACH0
AGND
ACH23
ACH22
ACH7
ACH6
AGND
ACH29
ACH28
ACH13
ACH12
AGND

Pin
2
4
6
8
10
12
14
16
18
20
22
24
26
28
30
32
34
36
38
40

Function
ACH19
ACH18
AGND
ACH11
ACH10
ACH25
ACH24
ACH9
ACH8
AGND
ACH31
ACH30
ACH15
ACH14
ACH21
ACH20
ACH5
ACH4
AGND
AGND

Table 19. Connector J5 differential pinout
Pin
1
3
5
7
9
11
13
15
17
19
21
23
25
27
29
31
33
35
37
39

Function
ACH11 LO
ACH10 LOAGND
ACH3 HI
ACH2 HI
ACH9 HI
ACH8 HI
ACH1 HI
ACH0 HIAGND
ACH15 HI
ACH14 HI
ACH7 HI
ACH6 HIAGND
ACH13 LO
ACH12 LO
ACH5 LO
ACH4 LO
AGND

Pin
2
4
6
8
10
12
14
16
18
20
22
24
26
28
30
32
34
36
38
40

54

Function
ACH11 HI
ACH10 HIAGND
ACH3 LO
ACH2 LO
ACH9 LO
ACH8 LO
ACH1 LO
ACH0 LOAGND
ACH15 LO
ACH14 LO
ACH7 LO
ACH6 LO
ACH13 HI
ACH12 HI
ACH5 HI
ACH4 HI
AGND
AGND

USB-2537 User's Guide

Specifications

J6
Table 20. Connector J6 single-ended mode pinout
Pin
1
3
5
7
9
11
13
15
17
19
21
23
25
27
29
31
33
35
37
39

Function
ACH43
ACH35
AGND
ACH42
ACH34
AGND
ACH41
ACH33
ACH40
ACH32
ACH47
ACH39
ACH46
ACH38
AGND
ACH45
ACH37
ACH44
ACH36
AGND

Pin
2
4
6
8
10
12
14
16
18
20
22
24
26
28
30
32
34
36
38
40

Function
ACH59
ACH51
ACH58
ACH50
ACH57
ACH49
ACH56
ACH48
AGND
ACH63
ACH55
AGND
ACH62
ACH54
ACH61
ACH53
ACH60
ACH52
AGND
AGND

Table 21. Connector J6 differential pinout
Pin
1
3
5
7
9
11
13
15
17
19
21
23
25
27
29
31
33
35
37
39

Function
ACH19 LO
ACH19 HIAGND
ACH18 LO
ACH18 HIAGND
ACH17 LO
ACH17 HI
ACH16 LO
ACH16 HI
ACH23 LO
ACH23 HI
ACH22 LO
ACH22 HIAGND
ACH21 LO
ACH21 HI
ACH20 LO
ACH20 HI
AGND

Pin
2
4
6
8
10
12
14
16
18
20
22
24
26
28
30
32
34
36
38
40

55

Function
ACH27 LO
ACH27 HI
ACH26 LO
ACH26 HI
ACH25 LO
ACH25 HI
ACH24 LO
ACH24 HIAGND
ACH31 LO
ACH31 HIAGND
ACH30 LO
ACH30 HIACH29 LO
ACH29 HI
ACH28 LO
ACH28 HI
AGND
AGND

USB-2537 User's Guide

Specifications

J7
Table 22. Connector J7 pinout
Pin
1
3
5
7
9
11
13
15
17
19
21
23
25
27
29
31
33
35
37
39

Function
GND
A0
A1
A2
A3
GND
B0
B1
B2
B3
GND
C0
C1
C2
C3
GND
TMR0
CNT0
CNT2
GND

Pin
2
4
6
8
10
12
14
16
18
20
22
24
26
28
30
32
34
36
38
40

Function
XAPCR (input scan clock)
A4
A5
A6
A7
TTL TRG
B4B5B6
B7+5 V (see Note 7)
C4
C5
C6
C7
TMR1
CNT1
CNT3
GND
GND

J8
Table 23. Connector J8 pinout
Pin
1
3
5
7
9
11
13
15
17
19
21
23
25
27
29
31
33
35
37
39

Note 7:Note 8:Function+13 V (see Note 8)
NC
AGND
XDAC0
XDAC1
AGND
SelfCalAGND
TTL TRG
XAPCR (input scan clock)
GND (digital)NC+5 V (see Note 7)
NC
NC
NC
NC
NC
NC
NC

Pin
2
4
6
8
10
12
14
16
18
20
22
24
26
28
30
32
34
36
38
40

Function-13 V (see Note 8)
NC
AGND
XDAC2
XDAC3
AGND
SGND (low level sense - not for general use)
AGND
XDPCR (output scan clock)
GND (digital)
GND (digital)NC
AUX PWR (output - reserved)
NC
NC
NC
NC
NC
NC
NC

5 V output, ±20% tolerance, 2 mA USB powered, 10 mA using external power.
±13 V outputs, ±10% tolerance, 1 mA USB powered, 5 mA using external power

56

Specifications
USB-2537 User's Guide

TC connector (TB7)

TC CH 0
TC CH 1
TC CH 2
TC CH 3Standoff
AGND
ACH0 +
ACH8 (-)
ACH1 +
ACH9 (-)
ACH2 +
ACH10 (-)
ACH3 +
ACH11 (-)

Connector TB7 pinout

57

Measurement Computing Corporation
10 Commerce Way
Norton, Massachusetts 02766(508) 946-5100
Fax: (508) 946-9500
E-mail: info@mccdaq.com
www.mccdaq.com

NI Hungary Kft
H-4031 Debrecen, Hátar út 1/A, Hungary
Phone: +36 (52) 515400
Fax: +36 (52) 515414
http://hungary.ni.com/debrecen