Labjack Lju3-lv User manual

U3 Product Page

Published on LabJack (http://labjack.com)

Home > Printer-friendl y PDF > Printer-friendly PDF

U3 User's Guide

The complete user's guide for the U3, including documentation for the LabJackUD driver. Covers

hardware versions 1.20, 1.21, and 1.30 (LV/HV).

To make a PDF of the whole manual, click "Export all" towards the upper-right of this page. Doing so

converts these pages to a PDF on-the-fly, using the latest content, and can take 20-30 seconds.

Make sure you have a current browser (we mostly test in Firefox and Chrome) and the current version

of Acrobat Reader. If it is not working for you, rather than a normal click of "Export all" do a right-click

and select "Save link as" or similar. Then wait 20-30 seconds and a dialog box will pop up asking

you where to save the PDF. Then you can open it in the real Acrobat Reader, not embedded in a

browser. If you still have problems, try the "Print all" option instead. In addition, an export is attached

below, but will not always be the latest version.

If you are looking at a PDF or hardcopy, realize that the original is an online document at http://labjack.com/support/u3/users-guide.

Rather than using a PDF, though, we encourage you to use this web-based documentation. Some advantages:

We can quickly change or update content.

The site search includes the user's guide, forum, and all other resources at labjack.com. When you are looking for

something try using the site search.

For support, try going to the applicable user's guide page and post a comment. When appropriate we can then immediately

add/change content on that page to address the question.

One other trick worth mentioning, is to browse the table of contents to the left. Rather than clicking on all the links to browse, you

can click on the small black triangles to expand without reloading the whole page.

User's Guide

Preface

For the latest version of this and other documents, go to www.labjack.com.

Package Contents:

The normal retail packaged U3 (-LV or -HV):

U3 unit itself in red enclosure

USB cable (6 ft / 1.8 m)

Screwdriver

Warranty:

The LabJack U3 is covered by a 1 year limited warranty from LabJack Corporation, covering this product and parts against

defects in material or workmanship. The LabJack can be damaged by misconnection (such as connecting 120 VAC to any of the

screw terminals), and this warranty does not cover damage obviously caused by the customer. If you have a problem, contact

support@labjack.com for return authorization. In the case of warranty repairs, the customer is responsible for shipping to LabJack

Corporation, and LabJack Corporation will pay for the return shipping.

Limitation of Liability:

LabJack designs and manufactures measurement and automation peripherals that enable the connection of a PC to the real-

world. Although LabJacks have various redundant protection mechanisms, it is possible, in the case of improper and/or

unreasonable use, to damage the LabJack and even the PC to which it is connected. LabJack Corporation will not be liable for

any such damage.

Except as specified herein, LabJack Corporation makes no warranties, express or implied, including but not limited to any implied

warranty or merchantability or fitness for a particular purpose. LabJack Corporation shall not be liable for any special, indirect,

incidental or consequential damages or losses, including loss of data, arising from any cause or theory.

LabJacks and associated products are not designed to be a critical component in life support or systems where malfunction can

reasonably be expected to result in personal injury. Customers using these products in such applications do so at their own risk

and agree to fully indemnify LabJack Corporation for any damages resulting from such applications.

LabJack assumes no liability for applications assistance or customer product design. Customers are responsible for their

applications using LabJack products. To minimize the risks associated with customer applications, customers should provide

adequate design and operating safeguards.

Reproduction of products or written or electronic information from LabJack Corporation is prohibited without permission.

Reproduction of any of these with alteration is an unfair and deceptive business practice.

Conformity Information (FCC, CE, RoHS):

See the Conformity Page and the text below:

FCC PART 15 STATEMENTS:

This equipment has been tested and found to comply with the limits for a Class A digital device, pursuant to Part 15 of the FCC

Rules. These limits are designed to provide reasonable protection against harmful interference when the equipment is operated in

a commercial environment. This equipment generates, uses, and can radiate radio frequency energy and, if not installed and used

in accordance with the instruction manual, may cause harmful interference to radio communications. Operation of this equipment

in a residential area is likely to cause harmful interference in which case the user will be required to correct the interference at his

own expense. The end user of this product should be aware that any changes or modifications made to this equipment without the

approval of the manufacturer could result in the product not meeting the Class A limits, in which case the FCC could void the user's

authority to operate the equipment.

Declaration of Conformity:

Manufacturers Name: LabJack Corporation

Manufacturers Address: 3232 S Vance St STE 100, Lakewood, CO 80227, USA

Declares that the product

Product Name: LabJack U3 (-LV or -HV)

Model Number: LJU3 (-LV or -HV)

conforms to the following Product Specifications:

EN 55011 Class A

EN 61326-1: 2002 General Requirements

and is marked with CE

RoHS:

The U3 is RoHS compliant per the requirements of Directive 2002/95/EC.

1 - Installation

Windows

The LJUD driver requires a PC running Windows. For other operating systems, go to labjack.com for available support. Software

will be installed to the LabJack directory which defaults to c:\Program Files\LabJack\.

Install the software first by going to labjack.com/support/u3.

Connect the USB cable: The USB cable provides data and power. After the UD software installation is complete, connect the

hardware and Windows should prompt with “Found New Hardware” and shortly after the Found New Hardware Wizard will open.

When the Wizard appears allow Windows to install automatically by accepting all defaults.

Run LJControlPanel: From the Windows Start Menu, go to the LabJack group and run LJControlPanel. Click the “Find Devices”

button, and an entry should appear for the connected U3 showing the serial number. Click on the “USB – 1” entry below the serial

number to bring up the U3 configuration panel. Click on “Test” in the configuration panel to bring up the test panel where you can

view and control the various I/O on the U3.

If LJControlPanel does not find the U3, check Windows Device Manager to see if the U3 installed correctly. One way to get to the

Device Manager is:

Start => Control Panel => System => Hardware => Device Manager

The entry for the U3 should appear as in the following figure. If it has a yellow caution symbol or exclamation point symbol, right-

click and select “Uninstall” or “Remove”. Then disconnect and reconnect the U3 and repeat the Found New Hardware Wizard as

described above.

Correctly Functioning U3 in Windows Device Manager

Linux and Mac OS X

The Exodriver is the native USB driver for Linux and Mac OS X. With it you can use low-level functions to interact with your U3 over

USB. The LJUD driver, LJControlPanel and LJSelfUpgrade applications are not available for Linux or Mac OS X.

Download the Exodriver at labjack.com/support/software or labjack.com/support/linux-and-mac-os-x-drivers. For Mac OS X you

can use the Mac Installer for installation, otherwise use the source code and install script.

Mac OS X Installer

Unzip the contents of Exodriver_NativeUSB_Setup.zip and run Exodriver_NativeUSB_Setup.pkg. Then follow the installer’s

instructions to install the driver.

Source Code

Mac OS X Requirements

• OS X 10.5 or newer

• XCode developer tools

• libusb-1.0 library available at libusb.info

Linux Requirements

• Linux kernel 2.6.28 or newer.

• GNU C Compiler

• libusb-1.0 library and development files (header files)

Installation

To install the driver from source code, first unzip the contents of the Exodriver source code. Then run the following commands in a

terminal (replace <Exodriver-Source-Directory> with the directory you unzipped the Exodriver source code to):

cd <Exodriver-Source-Directory>

sudo ./install.sh

Follow the install script’s instructions to install the driver.

For more Exodriver installation information go to the Exodriver page at labjack.com/support/linux-and-mac-os-x-drivers. The

source code download’s README, INSTALL.Linux and INSTALL.MacOSX also provides more information. If you run into

problems, first take a look at the comments section of the Exodriver page as the issue may have been helped with previously.

After installation, to test your U3 connect it to your computer with a USB cable. The USB cable provides data and power. Build and

run one of the examples from the source code download. Alternatively, install LabJackPython (at

labjack.com/support/labjackpython) and run one of its examples.

1.1 - Control Panel Application (LJControlPanel)

The application LJControlPanel is included with the installation package below

LabJack Windows Driver and Software Installation Package

Name: LabJack-2014-10-14.exe

Size: 49.99 MB

Upload date: 2014-10-14 12:45

The LabJack Control Panel application (LJCP) handles configuration and testing of the UD series hardware. Click on the “Find

Devices” button to search for connected devices.

Figure 1-1. LJControlPanel Main Window

Figure 1-1 shows the results from a typical search. The application found two devices. The USB connection for a U3 has been

selected in Figure 1-1, bringing up the configuration window on the right side.

Refresh: Reload the window using values read from the device.

Write Values: Write the Local ID from the window to the device.

Config Defaults: Opens the window shown in Figure 1-2.

Reset: Click to reset the selected device.

Test: Opens the window shown in Figure 1-3.

Config Defaults:

This option provides control over the condition of the device at power-up or reset. Figure 1-2 shows a U3-HV with the factory

default power-up configuration, which means AIN0-AIN3 set to analog input, FIO4 to CIO3 set to digital input, analog outputs set to

minimum voltage (near 0), and timers/counters/watchdog disabled.

Figure 1-2. LJControlPanel U3 Configure Defaults Window

Write Factory Values: Clicking this will set everything back to the factory defaults and write those factory defaults to

nonvolatile memory.

Write Values: Change any desired settings, and then click this to write the new settings to nonvolatile memory.

Test Panel:

Figure 1-3 shows the test window for a U3 device. This window continuously (once per second) writes to and reads from the

selected LabJack.

Figure 1-3. LJControlPanel U3 Test Window

Any configuration done on this screen is not written to nonvolatile memory. These settings just affect the current condition of the

device, not the reset/power-up condition.

When the test panel first loads it sets everything to factory default, so previous settings (or reset/power-up settings) will not be

shown.

LJCP Settings:

Selecting Options=>Settings from the main LJControlPanel menu brings up the window shown in Figure 1-4. This window allows

some features to of the LJControlPanel application to be customized.

Figure 1-4. LJControlPanel Settings Window

Search for USB devices: If selected, LJControlPanel will include USB when searching for devices.

Search for Ethernet devices using UDP broadcast packet: Only applies to UE9 device.

Search for Ethernet devices using specified IP addresses: Only applies to UE9 device.

LJControlPanel is normally installed by the main LabJack installer, which is the link at the top of the page.

1.2 - Self-Upgrade Application (LJSelfUpgrade)

The processor in the U3 has field upgradeable flash memory. The self-upgrade application shown in Figure 1-5 programs the

latest firmware onto the processor.

USB is the only interface on the U3, and first found is the only option for self-upgrading the U3, so no changes are needed in the

“Connect by:” box. There must only be one U3 connected to the PC when running LJSelfUpgrade.

Click on “Get Version Numbers”, to find out the current firmware versions on the device. Then use the provided Internet link to go to

labjack.com and check for more recent firmware. Download firmware files to the …\LabJack\LJSelfUpgrade\upgradefiles\

directory.

Click the Browse button and select the upgrade file to program. Click the Program button to begin the self-upgrade process.

Figure 1-5. Self-Upgrade Application

If problems are encountered during programming, try the following:

1. Unplug the U3, wait 5 seconds then reconnect the U3. Click OK then press program again.

2. If step 1 does not fix the problem unplug the U3 and watch the LED while plugging the U3 back in. Follow the following steps

based on the LED's activity.

1. If the LED is blinking continuously (flash mode), connect a jumper between FIO4 and SPC (FIO0 to SCL on U3

1.20/1.21), then unplug the U3, wait 5 seconds and plug the U3 back in. Try programming again (disconnect the jumper

before programming).

2. If the LED blinks several times and stays on, connect a jumper between FIO5 and SPC (FIO1 to SCL on U3

1.20/1.21), then unplug the U3, wait 5 seconds and plug the U3 back in. Try programming again (disconnect the jumper

before programming).

3. If the LED blinks several times and stays off, the U3 is not enumerating. Please restart your computer and try to

program again.

4. If there is no LED activity, connect a jumper between FIO5 and SPC (FIO1 to SCL on U3 1.20/1.21), then unplug the

U3, wait 5 seconds and plug the U3 back in. If the LED is blinking continuously click OK and program again (after

removing the jumper). If the LED does not blink connect a jumper between FIO4 and SPC (FIO0 to SCL on U3

1.20/1.21), then unplug the U3, wait 5 seconds and plug the U3 back in.

5. If the LED does a repeating pattern of 3 blinks then pause, the U3 has detected internal memory corruption and

you will have to contact LabJack Support.

3. If there is no activity from the U3's LED after following the above steps, please contact support.

2 - Hardware Description

The U3 has 3 different I/O areas:

Communication Edge,

Screw Terminal Edge,

DB Edge.

The communication edge has a USB type B connector (with black cable

connected in Figure 2-1). All power and communication is handled by the

USB interface.

The screw terminal edge has convenient connections for the analog outputs

and 8 flexible I/O (digital I/O, analog inputs, timers, or counters). The screw

terminals are arranged in blocks of 4, with each block consisting of Vs, GND,

and two I/O. There is also a status LED located on the left edge.

The DB Edge has a D-sub type connectors called DB15 which has the 8 EIO

lines and 4 CIO lines. The EIO lines are flexible like the FIO lines, while the

CIO are dedicated digital I/O.

Figure 2-1. LabJack U3

2.1 - USB

For information about USB installation, see Section 1.

The U3 has a full-speed USB connection compatible with USB version 1.1 or 2.0. This connection provides communication and

power (Vusb). USB ground is connected to the U3 ground (GND), and USB ground is generally the same as the ground of the PC

chassis and AC mains.

The details of the U3 USB interface are handled by the high level drivers (Windows LabJackUD DLL), so the following information

is really only needed when developing low-level drivers.

The LabJack vendor ID is 0x0CD5. The product ID for the U3 is 0x0003.

The USB interface consists of the normal bidirectional control endpoint (0 OUT & IN), 3 used bulk endpoints (1 OUT, 2 IN, 3 IN),

and 1 dummy endpoint (3 OUT). Endpoint 1 consists of a 64 byte OUT endpoint (address = 0x01). Endpoint 2 consists of a 64

byte IN endpoint (address = 0x82). Endpoint 3 consists of a dummy OUT endpoint (address = 0x03) and a 64 byte IN endpoint

(address = 0x83). Endpoint 3 OUT is not supported by the firmware, and should never be used.

All commands should always be sent on Endpoint 1, and the responses to commands will always be on Endpoint 2. Endpoint 3 is

only used to send stream data from the U3 to the host.

2.2 - Status LED

There is a green status LED on the LabJack U3. This LED blinks on reset, and then remains steadily lit. Other LED behavior is

generally related to flash upgrade modes ("Section 1.2":/support/u3/users-guide/1.2).

Normal Power-Up Status LED Behavior: When the USB cable is connected to the U3, the Status LED blinks 5-6 times over 2

seconds and then remains solid on.

LED blinking continuously at about 4 Hz, even with no software running: This indicates that the U3 is in flash mode. See

Section 1.2 and reprogram the device.

2.3 - GND and SGND

The GND connections available at the screw-terminals and DB connectors provide a common ground for all LabJack functions. All

GND terminals are the same and connect to the same ground plane. This ground is the same as the ground line on the USB

connection, which is often the same as ground on the PC chassis and therefore AC mains ground.

SGND is located near the upper-left of the device. This terminal has a self-resetting thermal fuse in series with GND. This is often

a good terminal to use when connecting the ground from another separately powered system that could unknowingly already share

a common ground with the U3.

See the AIN, DAC, and Digital I/O Sections for more information about grounding.

2.4 - VS

The Vs terminals are designed as outputs for the internal supply voltage (nominally 5 volts). This will be the voltage provided from

the USB cable. The Vs connections are outputs, not inputs. Do not connect a power source to Vs in normal situations. All Vs

terminals are the same.

2.5 - Flexible I/O (FIO/EIO)

The FIO and EIO ports on the LabJack U3 can be individually configured as digital input, digital output, or analog input. This is

FIO0-EIO7 on the U3-LV (16 lines), or FIO4-EIO7 on the U3-HV (12 lines). In addition, up to 2 of these lines can be configured as

timers, and up to 2 of these lines can be configured as counters. If a line is configured as analog, it is called AINx according to the

following table:

AIN0

FIO0

AIN8

EIO0

AIN1

FIO1

AIN9

EIO1

AIN2

FIO2

AIN10

EIO2

AIN3

FIO3

AIN11

EIO3

AIN4

FIO4

AIN12

EIO4

AIN5

FIO5

AIN13

EIO5

AIN6

FIO6

AIN14

EIO6

AIN7

FIO7

AIN15

EIO7

Table 2.5-1. Analog Input Pin Locations

On the U3-HV, compared to the -LV, the first four flexible I/O are fixed as analog inputs (AIN0-AIN3) with a nominal ±10 volt input

range. All digital operations, including analog/digital configuration, are ignored on these 4 fixed analog inputs.

Timers and counters can appear on various pins, but other I/O lines never move. For example, Timer1 can appear anywhere from

FIO4 to EIO1, depending on TimerCounterPinOffset and whether Timer0 is enabled. On the other hand, FIO5 (for example), is

always on the screw terminal labeled FIO5, and AIN5 (if enabled) is always on that same screw terminal.

The first 8 flexible I/O lines (FIO0-FIO7) appear on built-in screw terminals. The other 8 flexible I/O lines (EIO0-EIO7) are available

on the DB15 connector.

Many software applications will need to initialize the flexible I/O to a known pin configuration. That requires calls to the low-level

functions ConfigIO and ConfigTimerClock. Following are the values to set the pin configuration to the factory default state:

Byte #

WriteMask

Write all parameters

TimerCounterConfig

No Timers/Counters. Offset = 4

DAC1 Enable

DAC1 Disabled. (Ignored on HW 1.3)

FIOAnalog

FIO all digital.

EIOAnalog

EIO all digital.

Table 2.5-2. ConfigIO Factory Default Values

Byte #

TimerClockConfig

130

Set clock to 48MHz.

TimerClockDivisor

Divisor = 0.

Table 2.5-3. ConfigTimerClock Factory Default Values

When using the high-level LabJackUD driver, this could be done with the following requests:

ePut (lngHandle, LJ_ioPUT_CONFIG, LJ_chNUMBER_TIMERS_ENABLED, 0, 0);

ePut (lngHandle, LJ_ioPUT_CONFIG, LJ_chTIMER_COUNTER_PIN_OFFSET, 4, 0);

ePut (lngHandle, LJ_ioPUT_CONFIG, LJ_chTIMER_CLOCK_BASE, LJ_tc48MHZ, 0);

ePut (lngHandle, LJ_ioPUT_CONFIG, LJ_chTIMER_CLOCK_DIVISOR, 0, 0);

ePut (lngHandle, LJ_ioPUT_COUNTER_ENABLE, 0, 0, 0);

ePut (lngHandle, LJ_ioPUT_COUNTER_ENABLE, 1, 0, 0);

ePut (lngHandle, LJ_ioPUT_DAC_ENABLE, 1, 0, 0); //Ignored on hardware rev 1.30+.

ePut (lngHandle, LJ_ioPUT_ANALOG_ENABLE_PORT, 0, 0, 16);

… or with a single request to the following IOType created exactly for this purpose:

ePut (lngHandle, LJ_ioPIN_CONFIGURATION_RESET, 0, 0, 0);

2.6 - AIN

The LabJack U3 has up to 16 analog inputs available on the flexible I/O lines (FIO0-FIO7 and EIO0-EIO7). Single-ended

measurements can be taken of any line compared to ground, or differential measurements can be taken of any line to any other

line.

Analog input resolution is 12-bits. The range of single-ended analog inputs is normally about 0-2.44, and there is a “special” 0-3.6

volt range available. The range of differential analog inputs is typically ± 2.4 volts, but is pseudobipolar, not true bipolar. The

difference (positive channel minus negative channel) can be -2.4 volts, but neither input can have a voltage less than -0.3 volts to

ground. For valid measurements, the voltage on every low-voltage analog input pin, with respect to ground, must be within -0.3 to

+3.6 volts. See Appendix A for voltage limits to avoid damage.

On the U3-HV, compared to the -LV, the first four flexible I/O are fixed as analog inputs (AIN0-AIN3), and have scaling such that the

input range is a true bipolar ±10 volts normally, and -10 to +20 volts when using the “special” range. The input impedance of these

four lines is roughly 1 MΩ, which is good, but less than the normal low voltage analog inputs. Analog/digital configuration and all

other digital operations on these pins are ignored. FIO4-EIO7 are still available as flexible I/O, same as the U3-LV.

To get the special 0-3.6 volt or -10/+20 volt range, you do a differential reading with the negative channel set to 32, although the

reading is actually single-ended.

Because the scaling on the high-voltage inputs on the U3-HV (AIN0-AIN3) is inherently single-ended, a factory calibration is not

possible for differential readings. If a differential reading is requested where either channel is a high-voltage channel, the driver will

return the raw binary reading and the user must handle calibration/conversion.

The analog inputs have a QuickSample option where each conversion is done faster at the expense of increased noise. This is

enabled by passing a nonzero value for put_config special channel LJ_chAIN_RESOLUTION. There is also a LongSettling option

where additional settling time is added between the internal multiplexer configuration and the analog to digital conversion. This

allows signals with more source impedance, and is enabled by passing a nonzero value for put_config special channel

LJ_chAIN_SETTLING_TIME. Both of these options are disabled by default. This applies to command/response mode only, and

the resulting typical data rates are discussed in Section 3.1. For stream mode, see Section 3.2.

Note that sinking excessive current into digital outputs can cause substantial errors in analog input readings. See Section 2.8.1.4

for more info.

2.6.1 - Channel Numbers

The LabJack U3 has up to 16 external analog inputs, plus a few internal channels. The low-level functions specify a positive and

negative channel for each analog input conversion. With the LabJackUD driver, the IOType LJ_ioGET_AIN is used for single-

ended channels only, and thus the negative channel is internally set to 31. There is an additional IOType called

LJ_ioGET_AIN_DIFF that allows the user to specify the positive and negative channel.

Positive Channel #

0-7

AIN0-AIN7 (FIO0-FIO7)

8-15

AIN8-AIN15 (EIO0-EIO7)

Temp Sensor

Vreg

Table 2.6.1-1. Positive Channel Numbers

Negative Channel #

0-7

AIN0-AIN7 (FIO0-FIO7)

8-15

AIN8-AIN15 (EIO0-EIO7)

Vref

31 or 199

Single-Ended

Special 0-3.6 or -10/+20 (UD Only)

Table 2.6.1-2 Negative Channel Numbers

Positive channel 31 puts the internal Vreg (~3.3 volts) on the positive input of the ADC. See Section 2.6.4 for information about the

internal temperature sensor.

If the negative channel is set to anything besides 31/199, the U3 does a differential conversion and returns a pseudobipolar value.

If the negative channel is set to 31/199, the U3 does a single-ended conversion and returns a unipolar value. Channel 30 puts the

internal voltage reference Vref (~2.44 volts) on the negative input of the ADC.

Channel 32 is a special negative channel supported by the LabJack UD driver. When used, the driver will actually pass 30 as the

negative channel to the U3, and when the result is returned the driver adds Vref to the value. For a low-voltage analog input this

results in a full span on the positive channel of about 0 to 4.88 volts (versus ground), but since the voltage on any analog input

cannot exceed 3.6 volts, only 75% of the converter’s range is used and the span is about 0 to 3.6 volts. For a high-voltage analog

input, channel 32 (special range) results in a span of about -10 to +20 volts.

In the U3 examples that accompany the Exodriver, u3.c also supports channel 32 in calls to eAIN().

Channel 32 is also supported in LabJackPython:

# On the U3, wire a jumper from DAC0 to FIO0, then run:

>>> import u3

>>> d = u3.U3()

>>> d.configIO(FIOAnalog = 1) # Set FIO0 to analog

>>> d.writeRegister(5000, 3) # Set DAC0 to 3 V

>>> d.getAIN(0, 32)

3.0141140941996127

For the four high-voltage channels on the U3-HV, the special channel negative channel also puts Vref on the negative. This results

in an overall range of about -10 to +20 volts on the positive input.

2.6.2 - Converting Binary Readings to Voltages

This information is only needed when using low-level functions and other ways of getting binary readings. Readings in volts already

have the calibration constants applied. The UD driver, for example, normally returns voltage readings unless binary readings are

specifically requested.

Following are the nominal input voltage ranges for the low-voltage analog inputs. This is all analog inputs on the U3-LV, and AIN4-

AIN15 on the U3-HV.

Max V

Min V

Single-Ended

2.44

Differential

2.44

-2.44

Special 0-3.6

3.6

Table 2.6.2-1. Nominal Analog Input Voltage Ranges for Low-Voltage Channels

Max V

Min V

Single-Ended

10.3

-10.3

Differential

N/A

Special -10/+20

20.1

-10.3

Table 2.6.2-2. Nominal Analog Input Voltage Ranges for High-Voltage Channels

Note that the minimum differential input voltage of -2.44 volts means that the positive channel can be as much as 2.44 volts less

than the negative channel, not that a channel can measure 2.44 volts less than ground. The voltage of any low-voltage analog input

pin, compared to ground, must be in the range -0.3 to +3.6 volts.

The “special” range (0-3.6 on low-voltage channels and -10/+20 volts on high-voltage channels) is obtained by doing a differential

measurement where the negative channel is set to the internal Vref (2.44 volts). For low-voltage channels, simply do the low-

voltage differential conversion as described below, then add the stored Vref value. For high-voltage channels, do the same thing,

then multiply by the proper high-voltage slope, divide by the single-ended low-voltage slope, and add the proper high-voltage

offset. The UD driver handles these conversions automatically.

Although the binary readings have 12-bit resolution, they are returned justified as 16-bit values, so the approximate nominal

conversion from binary to voltage is:

Volts(uncalibrated) = (Bits/65536)*Span (Single-Ended)

Volts(uncalibrated) = (Bits/65536)*Span – Span/2 (Differential)

Binary readings are always unsigned integers.

Where span is the maximum voltage minus the minimum voltage from the tables above. The actual nominal conversions are

provided in the tables below, and should be used if the actual calibration constants are not read for some reason. Most

applications will use the actual calibrations constants (Slope and Offset) stored in the internal flash.

Volts = (Slope * Bits) + Offset

Since the U3 uses multiplexed channels connected to a single analog-to-digital converter (ADC), all low-voltage channels have the

same calibration for a given configuration. High-voltage channels have individual scaling circuitry out front, and thus the calibration

is unique for each channel.

See Section 5.4 for detail about the location of the U3 calibration constants.

2.6.2.1 - Analog Inputs With DAC1 Enabled (Hardware

Revisions 1.20 & 1.21 only)

This Section only applies to the older hardware revisions 1.20 and 1.21. Starting with hardware revision 1.30, DAC1 is always

enabled and does not affect the analog inputs.

The previous information assumed that DAC1 is disabled. If DAC1 is enabled, then the internal reference (Vref = 2.44 volts) is not

available for the ADC, and instead the internal regulator voltage (Vreg = 3.3 volts) is used as the reference for the ADC. Vreg is

not as stable as Vref, but more stable than Vs (5 volt power supply). Following are the nominal input voltage ranges for the analog

inputs, assuming that DAC1 is enabled.

Max V

Min V

Single-Ended

3.3

Differential

3.3

-3.3

Special -10/+20

N/A

Table 2.6.2.1-1. Nominal Analog Input Voltage Ranges (DAC1 Enabled)

Note that the minimum differential input voltage of -3.3 volts means that the positive channel can be as much as 3.3 volts less than

the negative channel, not that a channel can measure 3.3 volts less than ground. The voltage of any analog input pin, compared to

ground, must be in the range -0.3 to +3.6 volts, for specified performance. See Appendix A for voltage limits to avoid damage.

Negative channel numbers 30 and 32 are not valid with DAC1 enabled.

When DAC1 is enabled, the slope/offset calibration constants are not used to convert raw readings to voltages. Rather, the Vreg

value is retrieved from the Mem area, and used with the approximate single-ended or differential conversion equations above,

where Span is Vreg (single-ended) or 2Vreg (differential).

2.6.3 - Typical Analog Input Connections

A common question is “can this sensor/signal be measured with the U3”. Unless the signal has a voltage (referred to U3 ground)

beyond the limits in Appendix A , it can be connected without damaging the U3, but more thought is required to determine what is

necessary to make useful measurements with the U3 or any measurement device.

Voltage (versus ground): The single-ended analog inputs on the U3 measure a voltage with respect to U3 ground. The differential

inputs measure the voltage difference between two channels, but the voltage on each channel with respect to ground must still be

within the common mode limits specified in Appendix A. When measuring parameters other than voltage, or voltages too big or

too small for the U3, some sort of sensor or transducer is required to produce the proper voltage signal. Examples are a

temperature sensor, amplifier, resistive voltage divider, or perhaps a combination of such things.

Impedance: When connecting the U3, or any measuring device, to a signal source, it must be considered what impact the

measuring device will have on the signal. The main consideration is whether the currents going into or out of the U3 analog input

will cause noticeable voltage errors due to the impedance of the source. To maintain consistent 12-bit results, it is recommended

to keep the source impedance within the limits specified in Appendix A.

Resolution (and Accuracy): Based on the measurement type and resolution of the U3, the resolution can be determined in terms of

voltage or engineering units. For example, assume some temperature sensor provides a 0-10 mV signal, corresponding to 0-100

degrees C. Samples are then acquired with the U3 using the 0-2.44 volt single-ended input range, resulting in a voltage resolution

of about 2.44/4096 = 596 µV. That means there will be about 17 discrete steps across the 10 mV span of the signal, and the

temperature resolution is about 6 degrees C. If this experiment required a resolution of 1 degrees C, this configuration would not

be sufficient. Accuracy will also need to be considered. Appendix A places some boundaries on expected accuracy, but an in-

system calibration can generally be done to provide absolute accuracy down to the linearity (INL) limits of the U3.

Speed: How fast does the signal need to be sampled? For instance, if the signal is a waveform, what information is needed: peak,

average, RMS, shape, frequency, … ? Answers to these questions will help decide how many points are needed per waveform

cycle, and thus what sampling rate is required. In the case of multiple channels, the scan rate is also considered. See Sections 3.1

and 3.2.

2.6.3.1 - Signal from the LabJack

One example of measuring a signal from the U3 itself, is with an analog output. All I/O on the U3 share a common ground, so the

voltage on an analog output (DAC) can be measured by simply connecting a single wire from that terminal to an AIN terminal

(FIO/EIO). The analog output must be set to a voltage within the range of the analog input.

2.6.3.2 - Unpowered Isolated Signal

An example of an unpowered isolated signal would be a photocell where the sensor leads are not shorted to any external voltages.

Such a sensor typically has two leads, where the positive lead connects to an AIN terminal and the negative lead connects to a

GND terminal.

2.6.3.3 - Signal Powered By the LabJack

A typical example of this type of signal is a 3-wire temperature sensor. The sensor has a power and ground wire that connect to Vs

and GND on the LabJack, and then has a signal wire that simply connects to an AIN terminal.

Another variation is a 4-wire sensor where there are two signal wires (positive and negative) rather than one. If the negative signal

is the same as power ground, or can be shorted ground, then the positive signal can be connected to AIN and a single-ended

measurement can be made. A typical example where this does not work is a bridge type sensor, such as pressure sensor,

providing the raw bridge output (and no amplifier). In this case the signal voltage is the difference between the positive and

negative signal, and the negative signal cannot be shorted to ground. Such a signal could be measured using a differential input

on the U3.

2.6.3.4 - Signal Powered Externally

An example is a box with a wire coming out that is defined as a 0-2 volt analog signal and a second wire labeled as ground. The

signal is known to have 0-2 volts compared to the ground wire, but the complication is what is the voltage of the box ground

compared to the LabJack ground.

If the box is known to be electrically isolated from the LabJack, the box ground can simply be connected to LabJack GND. An

example would be if the box was plastic, powered by an internal battery, and does not have any wires besides the signal and

ground which are connected to AINx and GND on the LabJack.

If the box ground is known to be the same as the LabJack GND, then perhaps only the one signal wire needs to be connected to

the LabJack, but it generally does not hurt to go ahead and connect the ground wire to LabJack GND with a 100 Ω resistor. You

definitely do not want to connect the grounds without a resistor.

If little is known about the box ground, a DMM can be used to measure the voltage of box ground compared to LabJack GND. As

long as an extreme voltage is not measured, it is generally OK to connect the box ground to LabJack GND, but it is a good idea to

put in a 100 Ω series resistor to prevent large currents from flowing on the ground. Use a small wattage resistor (typically 1/8 or 1/4

watt) so that it blows if too much current does flow. The only current that should flow on the ground is the return of the analog input

bias current, which is only microamps.

The SGND terminals (on the same terminal block as SPC) can be used instead of GND for externally powered signals. A series

resistor is not needed as SGND is fused to prevent overcurrent, but a resistor will eliminate confusion that can be caused if the

fuse is tripping and resetting.

In general, if there is uncertainty, a good approach is to use a DMM to measure the voltage on each signal/ground wire without any

connections to the U3. If no large voltages are noted, connect the ground to U3 SGND with a 100 Ω series resistor. Then again use

the DMM to measure the voltage of each signal wire before connecting to the U3.

Another good general rule is to use the minimum number of ground connections. For instance, if connecting 8 sensors powered by

the same external supply, or otherwise referred to the same external ground, only a single ground connection is needed to the U3.

Perhaps the ground leads from the 8 sensors would be twisted together, and then a single wire would be connected to a 100 Ω

resistor which is connected to U3 ground.

2.6.3.5 - Amplifying Small Signal Voltages

The best results are generally obtained when a signal voltage spans the full analog input range of the LabJack. If the signal is too

small it can be amplified before connecting to the LabJack. One good way to handle low-level signals such as thermocouples is

the LJTick-InAmp, which is a 2-channel instrumentation amplifier module that plugs into the U3 screw-terminals.

For a do-it-yourself solution, the following figure shows an operational amplifier (op-amp) configured as non-inverting:

Figure 2.6-1. Non-Inverting Op-Amp Configuration

The gain of this configuration is:

Vout = Vin * (1 + (R2/R1))

100 kΩ is a typical value for R2. Note that if R2=0 (short-circuit) and R1=inf (not installed), a simple buffer with a gain equal to 1 is

the result.

There are numerous criteria used to choose an op-amp from the thousands that are available. One of the main criteria is that the

op-amp can handle the input and output signal range. Often, a single-supply rail-to-rail input and output (RIRO) is used as it can be

powered from Vs and GND and pass signals within the range 0-Vs. The OPA344 from Texas Instruments (ti.com) is good for many

5 volt applications.

The op-amp is used to amplify (and buffer) a signal that is referred to the same ground as the LabJack (single-ended). If instead

the signal is differential (i.e. there is a positive and negative signal both of which are different than ground), an instrumentation

amplifier (in-amp) should be used. An in-amp converts a differential signal to single-ended, and generally has a simple method to

set gain.

2.6.3.6 - Signal Voltages Beyond 0-2.44 Volts (and

Resistance Measurement)

The normal input range for a low voltage analog input channel (FIO/EIO) on the U3 is about 0-2.44 volts. There is also a Special 0-

3.6V range available on those inputs. The easiest way to handle larger voltages is often by using the LJTick-Divider, which is a two

channel buffered divider module that plugs into the U3 screw-terminals.

The basic way to handle higher unipolar voltages is with a resistive voltage divider. The following figure shows the resistive voltage

divider assuming that the source voltage (Vin) is referred to the same ground as the U3 (GND).

Figure 2.6-2. Voltage Divider Circuit

The attenuation of this circuit is determined by the equation:

Vout = Vin * ( R2 / (R1+R2))

This divider is easily implemented by putting a resistor (R1) in series with the signal wire, and placing a second resistor (R2) from

the AIN terminal to a GND terminal. To maintain specified analog input performance, R1 should not exceed the values specified in

Appendix A, so R1 can generally be fixed at the max recommended value and R2 can be adjusted for the desired attenuation.

The divide by 2 configuration where R1 = R2 = 10 kΩ (max source impedance limit for low-voltage channels), presents a 20 kΩ

load to the source, meaning that a 5 volt signal will have to be able to source/sink up to +250 µA. Some signal sources might

require a load with higher resistance, in which case a buffer should be used. The following figure shows a resistive voltage divider

followed by an op-amp configured as non-inverting unity-gain (i.e. a buffer).

Figure 2.6-3. Buffered Voltage Divider Circuit

The op-amp is chosen to have low input bias currents so that large resistors can be used in the voltage divider. For 0-5 volt

applications, where the amp will be powered from Vs and GND, a good choice would be the OPA344 from Texas Instruments

(ti.com). The OPA344 has a very small bias current that changes little across the entire voltage range. Note that when powering the

amp from Vs and GND, the input and output to the op-amp is limited to that range, so if Vs is 4.8 volts your signal range will be 0-

4.8 volts.

To handle bipolar voltages, you also need offset or level-shifting. Refer to application note SLOA097 from ti.com for more

information.

The information above also applies to resistance measurement. A common way to measure resistance is to build a voltage

divider as shown in Figure 2.6-2, where one of the resistors is known and the other is the unknown. If Vin is known and Vout is

measured, the voltage divider equation can be rearranged to solve for the unknown resistance.

2.6.3.7 - Measuring Current (Including 4-20 mA) with a

Resistive Shunt

The best way to handle 4-20 mA signals is with the LJTick-CurrentShunt, which is a two channel active current to voltage converter

module that plugs into the UE9 screw-terminals.

The following figure shows a typical method to measure the current through a load, or to measure the 4-20 mA signal produced by

a 2-wire (loop-powered) current loop sensor. The current shunt shown in the figure is simply a resistor.

Figure 2.6-4. Current Measurement With Arbitrary Load or 2-Wire 4-20 mA Sensor

When measuring a 4-20 mA signal, a typical value for the shunt would be 120 Ω. This results in a 0.48 to 2.40 volt signal

corresponding to 4-20 mA. The external supply must provide enough voltage for the sensor and the shunt, so if the sensor requires

5 volts the supply must provide at least 7.4 volts.

For applications besides 4-20 mA, the shunt is chosen based on the maximum current and how much voltage drop can be

tolerated across the shunt. For instance, if the maximum current is 1.0 amp, and 1.0 volts of drop is the most that can be tolerated

without affecting the load, a 1.0 Ω resistor could be used. That equates to 1.0 watts, though, which would require a special high

wattage resistor. A better solution would be to use a 0.1 Ω shunt, and then use an amplifier to increase the small voltage produced

by that shunt. If the maximum current to measure is too high (e.g. 100 amps), it will be difficult to find a small enough resistor and a

hall-effect sensor should be considered instead of a shunt.

The following figure shows typical connections for a 3-wire 4-20 mA sensor. A typical value for the shunt would be 120 Ω which

results in 0.48 to 2.40 volts.

Figure 2.6-5. Current Measurement With 3-Wire 4-20 mA (Sourcing) Sensor

The sensor shown in the above figure is a sourcing type, where the signal sources the 4-20 mA current which is then sent through

the shunt resistor and sunk into ground. Another type of 3-wire sensor is the sinking type, where the 4-20 mA current is sourced

from the positive supply, sent through the shunt resistor, and then sunk into the signal wire. If sensor ground is connected to U3

ground, the sinking type of sensor presents a problem, as at least one side of the resistor has a high common mode voltage

(equal to the positive sensor supply). If the sensor is isolated, a possible solution is to connect the sensor signal or positive sensor

supply to U3 ground (instead of sensor ground). This requires a good understanding of grounding and isolation in the system. The

LJTick-CurrentShunt is often a simple solution.

Both figures show a 0-100 Ω resistor in series with SGND, which is discussed in general in Section 2.6.3.4. In this case, if SGND

is used (rather than GND), a direct connection (0 Ω) should be good.

The best way to handle 4-20 mA signals is with the LJTick-CurrentShunt, which is a two channel active current to voltage converter

module that plugs into the U3 screw-terminals.

2.6.3.8 - Floating/Unconnected Inputs

The reading from a floating (no external connection) analog input channel can be tough to predict and is likely to vary with sample

timing and adjacent sampled channels. Keep in mind that a floating channel is not at 0 volts, but rather is at an undefined voltage.

In order to see 0 volts, a 0 volt signal (such as GND) should be connected to the input.

Some data acquisition devices use a resistor, from the input to ground, to bias an unconnected input to read 0. This is often just

for “cosmetic” reasons so that the input reads close to 0 with floating inputs, and a reason not to do that is that this resistor can

degrade the input impedance of the analog input.

In a situation where it is desired that a floating channel read a particular voltage, say to detect a broken wire, a resistor (pull-down

or pull-up) can be placed from the AINx screw terminal to the desired voltage (GND, VS, DACx, …). A 100 kΩ resistor should pull

the analog input readings to within 50 mV of any desired voltage, but obviously degrades the input impedance to 100 kΩ. For the

specific case of pulling a floating channel to 0 volts, a 1 MΩ resistor to GND can typically be used to provide analog input readings

of less than 50 mV. This information is for a low-voltage analog input channel on a U3.

Note that the four high-voltage channels on the U3-HV do sit at a predictable 1.4 volts. You can use a pull-down or pull-up resistor

with the high-voltage inputs, but because their input impedance is lower the resistor must be lower (~1k might be typical) and thus

the signal is going to have to drive substantial current.

2.6.3.9 - Signal Voltages Near Ground

The nominal input range of a low-voltage single-ended analog input is 0-2.44 volts. So the nominal minimum voltage is 0.0 volts,

but the variation in that minimum can be about +/-40 mV, and thus the actual minimum voltage could be 0.04 volts.

This is not an offset error, but just a minimum limit. Assume the minimum limit of your U3 happens to be 10 mV. If you apply a

voltage of 0.02 volts it will read 0.02 volts. If you apply a voltage of 0.01 volts it will read 0.01 volts. If you apply a voltage less than

0.01 volts, however, it will still read the minimum limit of 0.01 volts in this case.

One impact of this, is that a short to GND is usually not a good test for noise and accuracy. We often use a 1.5 volt battery for

simple tests.

If performance all the way to 0.0 is needed, use a differential reading (which is pseudobipolar). Connect some other channel to

GND with a small jumper, and then take a differential reading of your channel compared to that grounded channel.

The nominal input range of a high-voltage single-ended analog input is +/-10 volts, so readings around 0.0 are right in the middle

of the range and not an issue.

2.6.4 - Internal Temperature Sensor

The U3 has an internal temperature sensor. Although this sensor measures the temperature inside the U3, which is warmer than

ambient, it has been calibrated to read actual ambient temperature, although should only be expected to be accurate to within a

few degrees C. For best results the temperature of the entire U3 must stabilize relative to the ambient temperature, which can take

on the order of 1 hour. Best results will be obtained in still air in an environment with slowly changing ambient temperatures.

With the UD driver, the internal temperature sensor is read by acquiring single-ended analog input channel 30, and returns

degrees K. Use channel 30 anywhere you would use an analog input channel (e.g. with eAIN).

2.7 - DAC

The LabJack U3 has 2 analog outputs (DAC0 and DAC1) that are available on the screw terminals. Each analog output can be

set to a voltage between about 0.04 and 4.95 volts with 10 bits of resolution (8 bits on older hardware revision 1.20/1.21). The

maximum output voltage is limited by the supply voltage to the U3.

Starting with hardware revision 1.30, DAC1 is always enabled and does not affect the analog inputs, but with older hardware the

second analog output is only available in certain configurations. With hardware revisions <1.30, if the analog inputs are using the

internal 2.4 volt reference (the most accurate option), then DAC1 outputs a fixed voltage of 1.5*Vref. Also with hardware revisions

<1.30, if DAC1 is enabled the analog inputs use Vreg (3.3 volts) as the ADC reference, which is not as stable as the internal 2.4

volt reference.

The DAC outputs are derived as a percentage of Vreg, and then amplified by 1.5, so any changes in Vreg will have a

proportionate affect on the DAC outputs. Vreg is more stable than Vs (5 volt supply voltage), as it is the output from a 3.3 volt

regulator.

The DACs are derived from PWM signals that are affected by the timer clock frequency (Section 2.9). The default timer clock

frequency of the U3 is set to 48 MHz, and this results in the minimum DAC output noise. If the frequency is lowered, the DACs will

have more noise, where the frequency of the noise is the timer clock frequency divided by 65536. This effect is more exaggerated

with the 10-bit DACs on hardware revision 1.30+, compared to the 8-bit DACs on previous hardware revisions. The noise with a

timer clock of 48/12/4/1 MHz is roughly 5/20/100/600 mV. If lower noise performance is needed at lower timer clock frequencies,

use the power-up default setting in LJControlPanel to force the device to use 8-bit DAC mode (uses the low-level

CompatibilityOptions byte documented in Section 5.2.2). A large capacitor (at least 220 uF) from DACn to GND can also be used

to reduce noise.

The analog outputs have filters with a 3 dB cutoff around 16 Hz, limiting the frequency of output waveforms to less than that.

The analog output commands are sent as raw binary values (low level functions). For a desired output voltage, the binary value can

be approximated as:

Bits(uncalibrated) = (Volts/4.95)*256

For a proper calculation, though, use the calibration values (Slope and Offset) stored in the internal flash on the processor (Section

5.4):

Bits = (Slope * Volts) + Offset

The previous apply when using the original 8-bit DAC commands supported on all hardware versions. To take advantage of the

10-bit resolution on hardware revision 1.30, new commands have been added (Section 5.2.5) where the binary values are aligned

to 16-bits. The cal constants are still aligned to 8-bits, however, so the slope and offset should each be multiplied by 256 before

using in the above formula.

The analog outputs can withstand a continuous short-circuit to ground, even when set at maximum output.

Voltage should never be applied to the analog outputs, as they are voltage sources themselves. In the event that a voltage is

accidentally applied to either analog output, they do have protection against transient events such as ESD (electrostatic

discharge) and continuous overvoltage (or undervoltage) of a few volts.

There is an accessory available from LabJack called the LJTick-DAC that provides a pair of 14-bit analog outputs with a range of

±10 volts. The LJTick-DAC plugs into any digital I/O block, and thus up to 10 of these can be used per U3 to add 20 analog

outputs. The LJTick-DAC has various improvements compared to the built-in DACs on the U3:

Range of +10.0 to -10.0 volts.

Resolution of 14-bits.

Slew rate of 0.1 V/μs.

Based on a reference, rather than regulator, so more accurate and stable.

Does not affect analog inputs in any configuration.

2.7.1 - Typical Analog Output Connections

2.7.1.1 - High Current Output

The DACs on the U3 can output quite a bit of current, but they have 50 Ω of source impedance that will cause voltage drop. To

avoid this voltage drop, an op-amp can be used to buffer the output, such as the non-inverting configuration shown in Figure 2-3. A

simple RC filter can be added between the DAC output and the amp input for further noise reduction. Note that the ability of the

amp to source/sink current near the power rails must still be considered. A possible op-amp choice would be the TLV246x family

(ti.com).

2.7.1.2 - Different Output Ranges

See the end of this section for information about the LJTick-DAC which has a +/-10V range.

The typical output range of the DACs is about 0.04 to 4.95 volts. For other unipolar ranges, an op-amp in the non-inverting

configuration (Figure 2.6-1) can be used to provide the desired gain. For example, to increase the maximum output from 4.95 volts

to 10.0 volts, a gain of 2.02 is required. If R2 (in Figure 2-3) is chosen as 100 kΩ, then an R1 of 97.6 kΩ is the closest 1% resistor

that provides a gain greater than 2.02. The +V supply for the op-amp would have to be greater than 10 volts.

For bipolar output ranges, such as ±10 volts, a similar op-amp circuit can be used to provide gain and offset, but of course the op-

amp must be powered with supplies greater than the desired output range (depending on the ability of the op-amp to drive it’s

outputs close to the power rails). If ±10, ±12, or ±15 volt supplies are available, consider using the LT1490A op-amp (linear.com),

which can handle a supply span up to 44 volts.

A reference voltage is also required to provide the offset. In the following circuit, DAC1 is used to provide a reference voltage. The

actual value of DAC1 can be adjusted such that the circuit output is 0 volts at the DAC0 mid-scale voltage, and the value of R1 can

be adjusted to get the desired gain. A fixed reference (such as 2.5 volts) could also be used instead of DAC1.

Figure 2.7-1. ±10 Volt DAC Output Circuit

A two-point calibration should be done to determine the exact input/output relationship of this circuit. Refer to application note

SLOA097 from ti.com for further information about gain and offset design with op-amps.

LJTick-DAC:

There is an accessory available from LabJack called the LJTick-DAC that provides a pair of 14-bit analog outputs with a range of

±10 volts. The LJTick-DAC plugs into any digital I/O block, and thus up to 10 of these can be used per U3 to add 20 analog

outputs. The LJTick-DAC has various improvements compared to the built-in DACs on the U3:

Range of +10.0 to -10.0 volts.

Resolution of 14-bits.

Slew rate of 0.1 V/μs.

Based on a reference, rather than regulator, so more accurate and stable.

Does not affect analog inputs in any configuration.

2.8 - Digital I/O

The LabJack U3 has up to 20 digital I/O channels. 16 are available from the flexible I/O lines, and 4 dedicated digital I/O (CIO0-

CIO3) are available on the DB15 connector. The first 4 lines, FIO0-FIO3, are unavailable on the U3-HV. Each digital line can be

individually configured as input, output-high, or output-low. The digital I/O use 3.3 volt logic and are 5 volt tolerant.

The LabJackUD driver uses the following bit numbers to specify all the digital lines:

0-7 FIO0-FIO7 (0-3 unavailable on U3-HV)

8-15 EIO0-EIO7

16-19 CIO0-CIO3

The 8 FIO lines appear on the built-in screw-terminals, while the 8 EIO and 4 CIO lines appear only on the DB15 connector. See

the DB15 Section of this User’s Guide for more information.

All the digital I/O include an internal series resistor that provides overvoltage/short-circuit protection. These series resistors also

limit the ability of these lines to sink or source current. Refer to the specifications in Appendix A.

All digital I/O on the U3 have 3 possible states: input, output-high, or output-low. Each bit of I/O can be configured individually.

When configured as an input, a bit has a ~100 kΩ pull-up resistor to 3.3 volts (all digital I/O are 5 volt tolerant). When configured as

output-high, a bit is connected to the internal 3.3 volt supply (through a series resistor). When configured as output-low, a bit is

connected to GND (through a series resistor).

The fact that the digital I/O are specified as 5-volt tolerant means that 5 volts can be connected to a digital input without problems

(see the actual limits in the specifications in Appendix A). If 5 volts is needed from a digital output, consider the following solutions:

In some cases, an open-collector style output can be used to get a 5V signal. To get a low set the line to output-low, and to

get a high set the line to input. When the line is set to input, the voltage on the line is determined by a pull-up resistor. The

U3 has an internal ~100k resistor to 3.3V, but an external resistor can be added to a different voltage. Whether this will work

depends on how much current the load is going to draw and what the required logic thresholds are. Say for example a 10k

resistor is added from EIO0 to VS. EIO0 has an internal 100k pull-up to 3.3 volts and a series output resistance of about 180

ohms. Assume the load draws just a few microamps or less and thus is negligible. When EIO0 is set to input, there will be

100k to 3.3 volts in parallel with 10k to 5 volts, and thus the line will sit at about 4.85 volts. When the line is set to output-low,

there will be 180 ohms in series with the 10k, so the line will be pulled down to about 0.1 volts.

The surefire way to get 5 volts from a digital output is to add a simple logic buffer IC that is powered by 5 volts and

recognizes 3.3 volts as a high input. Consider the CD74ACT541E from TI (or the inverting CD74ACT540E). All that is

needed is a few wires to bring VS, GND, and the signal from the LabJack to the chip. This chip can level shift up to eight

0/3.3 volt signals to 0/5 volt signals and provides high output drive current (+/-24 mA).

Note that the 2 DAC channels on the U3 can be set to 5 volts, providing 2 output lines with such capability.

The power-up condition of the digital I/O can be configured by the user with the "Config Defaults" option in LJControlPanel. From

the factory, all digital I/O are configured to power-up as inputs. Note that even if the power-up default for a line is changed to

output-high or output-low, there is a delay of about 5 ms at power-up where all digital I/O are in the factory default condition.

If you want a floating digital input to read low, an external pull-down resistor can be added to overpower the internal 100k pull-up.

4.7k to 22k would be a typical range for this pull-down, with 10k being a solid choice for most applications.

The low-level Feedback function (Section 5.2.5) writes and reads all digital I/O. For information about using digital I/O under the

Windows LabJackUD driver, see Section 4.3.5. See Section 3.1 for timing information.

Many function parameters contain specific bits within a single integer parameter to write/read specific information. In particular,

most digital I/O parameters contain the information for each bit of I/O in one integer, where each bit of I/O corresponds to the same

bit in the parameter (e.g. the direction of FIO0 is set in bit 0 of parameter FIODir). For instance, in the low-level function ConfigU3,

the parameter FIODirection is a single byte (8 bits) that writes/reads the power-up direction of each of the 8 FIO lines:

if FIODirection is 0, all FIO lines are input,

if FIODirection is 1 (20), FIO0 is output, FIO1-FIO7 are input,

if FIODirection is 5 (20 + 22), FIO0 and FIO2 are output, all other FIO lines are input,

if FIODirection is 255 (20 + … + 27), FIO0-FIO7 are output.

2.8.1 - Typical Digital I/O Connections

2.8.1.1 - Input: Driven Signals

The most basic connection to a U3 digital input is a driven signal, often called push-pull. With a push-pull signal the source is

typically providing a high voltage for logic high and zero volts for logic low. This signal is generally connected directly to the U3

digital input, considering the voltage specifications in Appendix A . If the signal is over 5 volts, it can still be connected with a series

resistor. The digital inputs have protective devices that clamp the voltage at GND and VS, so the series resistor is used to limit the

current through these protective devices. For instance, if a 24 volt signal is connected through a 22 kΩ series resistor, about 19

volts will be dropped across the resistor, resulting in a current of 0.9 mA, which is no problem for the U3. The series resistor should

be 22 kΩ or less, to make sure the voltage on the I/O line when low is pulled below 0.8 volts.

The other possible consideration with the basic push-pull signal is the ground connection. If the signal is known to already have a

common ground with the U3, then no additional ground connection is used. If the signal is known to not have a common ground

with the U3, then the signal ground can simply be connected to U3 GND. If there is uncertainty about the relationship between

signal ground and U3 ground (e.g. possible common ground through AC mains), then a ground connection with a ~10 Ω series

resistor is generally recommended (see Section 2.6.3.4).

Figure 2.8-1. Driven Signal Connection To Digital Input

Figure 2.8-1 shows typical connections. Rground is typically 0-100 Ω. Rseries is typically 0 Ω (short-circuit) for 3.3/5 volt logic, or

22 kΩ (max) for high-voltage logic. Note that an individual ground connection is often not needed for every signal. Any signals

powered by the same external supply, or otherwise referred to the same external ground, should share a single ground connection

to the U3 if possible.

When dealing with a new sensor, a push-pull signal is often incorrectly assumed when in fact the sensor provides an open-collector

signal as described next.

2.8.1.2 - Input: Open-Collector Signals

Open-collector (also called open-drain or NPN) is a very common type of digital signal. Rather than providing 5 volts and ground,

like the push-pull signal, an open-collector signal provides ground and high-impedance. This type of signal can be thought of as a

switch connected to ground. Since the U3 digital inputs have a 100 kΩ internal pull-up resistor, an open-collector signal can

generally be connected directly to the input. When the signal is inactive, it is not driving any voltage and the pull-up resistor pulls the

digital input to logic high. When the signal is active, it drives 0 volts which overpowers the pull-up and pulls the digital input to logic

low. Sometimes, an external pull-up (e.g. 4.7 kΩ from Vs to digital input) will be installed to increase the strength and speed of the

logic high condition.

Figure 2.8-2. Open-Collector (NPN) Connection To Digital Input

Figure 2.8-2 shows typical connections. Rground is typically 0-100 Ω, Rseries is typically 0 Ω, and Rpullup, the external pull-up

resistor, is generally not required. If there is some uncertainty about whether the signal is really open-collector or could drive a

voltage beyond 5.8 volts, use an Rseries of 22 kΩ as discussed in Section 2.8.1.1, and the input should be compatible with an

open-collector signal or a driven signal up to at least 48 volts.

Without the optional resistors, the figure simplifies to:

Figure 2.8-3. Simplified Open-Collector (NPN) Connection To Digital Input Without Optional Resistors

Note that an individual ground connection is often not needed for every signal. Any signals powered by the same external supply,

or otherwise referred to the same external ground, should share a single ground connection to the U3 if possible.

2.8.1.3 - Input: Mechanical Switch Closure

To detect whether a mechanical switch (dry contact) is open or closed, connect one side of the switch to U3 ground and the other

side to a digital input. The behavior is very similar to the open-collector described above.

Figure 2.8-4. Basic Mechanical Switch Connection To Digital Input

When the switch is open, the internal 100 kΩ pull-up resistor will pull the digital input to about 3.3 volts (logic high). When the switch

is closed, the ground connection will overpower the pull-up resistor and pull the digital input to 0 volts (logic low). Since the

mechanical switch does not have any electrical connections, besides to the LabJack, it can safely be connected directly to GND,

without using a series resistor or SGND.

When the mechanical switch is closed (and even perhaps when opened), it will bounce briefly and produce multiple electrical

edges rather than a single high/low transition. For many basic digital input applications, this is not a problem as the software can

simply poll the input a few times in succession to make sure the measured state is the steady state and not a bounce. For

applications using timers or counters, however, this usually is a problem. The hardware counters, for instance, are very fast and will

increment on all the bounces. Some solutions to this issue are:

Software Debounce: If it is known that a real closure cannot occur more than once per some interval, then software can be

used to limit the number of counts to that rate.

Firmware Debounce: See Section 2.9.1 for information about timer mode 6.

Active Hardware Debounce: Integrated circuits are available to debounce switch signals. This is the most reliable hardware

solution. See the MAX6816 (maxim-ic.com) or EDE2008 (elabinc.com).

Passive Hardware Debounce: A combination of resistors and capacitors can be used to debounce a signal. This is not

foolproof, but works fine in most applications.

Figure 2.8-5. Passive Hardware Debounce

Figure 2.8-5 shows one possible configuration for passive hardware debounce. First, consider the case where the 1 kΩ resistor is

replaced by a short circuit. When the switch closes it immediately charges the capacitor and the digital input sees logic low, but

when the switch opens the capacitor slowly discharges through the 22 kΩ resistor with a time constant of 22 ms. By the time the

capacitor has discharged enough for the digital input to see logic high, the mechanical bouncing is done. The main purpose of the

1 kΩ resistor is to limit the current surge when the switch is closed. 1 kΩ limits the maximum current to about 5 mA, but better

results might be obtained with smaller resistor values.

2.8.1.4 - Output: Controlling Relays

All the digital I/O lines have series resistance that restricts the amount of current they can sink or source, but solid-state relays

(SSRs) can usually be controlled directly by the digital I/O. The SSR is connected as shown in the following diagram, where VS (~5

volts) connects to the positive control input and the digital I/O line connects to the negative control input (sinking configuration).

Figure 2.8-6. Relay Connections (Sinking Control, High-Side Load Switching)

When the digital line is set to output-low, control current flows and the relay turns on. When the digital line is set to input, control

current does not flow and the relay turns off. When the digital line is set to output-high, some current flows, but whether the relay is

on or off depends on the specifications of a particular relay. It is recommended to only use output-low and input.

For example, the Series 1 (D12/D24) or Series T (TD12/TD24) relays from Crydom specify a max turn-on of 3.0 volts, a min turn-

off of 1.0 volts, and a nominal input impedance of 1500 Ω.

When the digital line is set to output-low, it is the equivalent of a ground connection with 180 Ω (EIO/CIO) or 550 Ω (FIO) in

series. When using an EIO/CIO line, the resulting voltage across the control inputs of the relay will be about

5*1500/(1500+180) = 4.5 volts (the other 0.5 volts is dropped across the internal resistance of the EIO/CIO line). With an FIO

line the voltage across the inputs of the relay will be about 5*1500/(1500+550) = 3.7 volts (the other 1.3 volts are dropped

across the internal resistance of the FIO line). Both of these are well above the 3.0 volt threshold for the relay, so it will turn on.

When the digital line is set to input, it is the equivalent of a 3.3 volt connection with 100 kΩ in series. The resulting voltage

across the control inputs of the relay will be close to zero, as virtually all of the 1.7 volt difference (between VS and 3.3) is

dropped across the internal 100 kΩ resistance. This is well below the 1.0 volt threshold for the relay, so it will turn off.

When the digital line is set to output-high, it is the equivalent of a 3.3 volt connection with 180 Ω (EIO/CIO) or 550 Ω (FIO) in

series. When using an EIO/CIO line, the resulting voltage across the control inputs of the relay will be about

1.7*1500/(1500+180) = 1.5 volts. With an FIO line the voltage across the inputs of the relay will be about

1.7*1500/(1500+550) = 1.2 volts. Both of these in the 1.0-3.0 volt region that is not defined for these example relays, so the

resulting state is unknown.

Note that sinking excessive current into digital outputs can cause noticeable shifts in analog input readings. For example, the FIO

sinking configuration above sinks about 2.4 mA into the digital output to turn the SSR on, which could cause a shift of roughly 1 mV

to analog input readings.

Mechanical relays require more control current than SSRs, and cannot be controlled directly by the digital I/O on the U3. To control

higher currents with the digital I/O, some sort of buffer is used. Some options are a discrete transistor (e.g. 2N2222), a specific

chip (e.g. ULN2003), or an op-amp.

Note that the U3 DACs can source enough current to control almost any SSR and even some mechanical relays, and thus can be

a convenient way to control 1 or 2 relays. With the DACs you would typically use a sourcing configuration (DAC/GND) rather than

sinking (VS/DAC).

The RB12 relay board is a useful accessory available from LabJack. This board connects to the DB15 connector on the U3 and

accepts up to 12 industry standard I/O modules (designed for Opto22 G4 modules and similar).

Another accessory available from LabJack is the LJTick-RelayDriver. This is a two channel module that plugs into the U3 screw-

terminals, and allows two digital lines to each hold off up to 50 volts and sink up to 200 mA. This allows control of virtually any solid-

state or mechanical relay.

2.9 - Timers/Counters

The U3 has 2 timers (Timer0-Timer1) and 2 counters (Counter0-Counter1). When any of these timers or counters are enabled, they

take over an FIO/EIO line in sequence (Timer0, Timer1, Counter0, then Counter1), starting with FIO0+TimerCounterPinOffset.

Some examples:

1 Timer enabled, Counter0 disabled, Counter1 disabled, and TimerCounterPinOffset=4:

FIO4=Timer0

1 Timer enabled, Counter0 disabled, Counter1 enabled, and TimerCounterPinOffset=6:

FIO6=Timer0

FIO7=Counter1

2 Timers enabled, Counter0 enabled, Counter1 enabled, and TimerCounterPinOffset=8:

EIO0=Timer0

EIO1=Timer1

EIO2=Counter0

EIO3=Counter1

Starting with hardware revision 1.30, timers/counters cannot appear on FIO0-3, and thus TimerCounterPinOffset must be 4-8.

A value of 0-3 will result in an error. This error can be suppressed by a power-up default setting in LJControlPanel. If suppressed, a

0-3 will result in an offset of 4.

Timers and counters can appear on various pins, but other I/O lines never move. For example, Timer1 can appear anywhere from

FIO4 to EIO1, depending on TimerCounterPinOffset and whether Timer0 is enabled. On the other hand, FIO5 (for example), is

always on the screw terminal labeled FIO5, and AIN5 (if enabled) is always on that same screw terminal.

Note that Counter0 is not available with certain timer clock base frequencies. In such a case, it does not use an external FIO/EIO

pin. An error will result if an attempt is made to enable Counter0 when one of these frequencies is configured. Similarly, an error

will result if an attempt is made to configure one of these frequencies when Counter0 is enabled.

Applicable digital I/O are automatically configured as input or output as needed when timers and counters are enabled, and stay

that way when the timers/counters are disabled.

See Section 2.8.1 for information about signal connections.

Each counter (Counter0 or Counter1) consists of a 32-bit register that accumulates the number of falling edges detected on the

external pin. If a counter is reset and read in the same function call, the read returns the value just before the reset.

The timers (Timer0-Timer1) have various modes available:

Index (Low-level & UD)

16-bit PWM output

8-bit PWM output

Period input (32-bit, rising edges)

Period input (32-bit, falling edges)

Duty cycle input

Firmware counter input

Firmware counter input (with debounce)

Frequency output

Quadrature input

Timer stop input (odd timers only)

System timer low read (default mode)

System timer hight read

Period input (16-bit, rising edges)

Period input (16-bit, falling edges)

Table 2.9-1. U3 Timer Modes

Both timers use the same timer clock.

There are 7 choices for the timer clock base:

Index (Low-level/UD)

0/20

4 MHz

1/21

12 MHz

2/22

48 MHz (default)

3/23

1 MHz /Divisor

4/24

4 MHz /Divisor

5/25

12 MHz /Divisor

6/26

48 MHz /Divisor

Table 2.9-2. U3 Timer Clock Base Options

Note that these clocks apply to the U3 hardware revision 1.21+. With hardware revision 1.20 all clocks are half of the values

above.

The first 3 clocks have a fixed frequency, and are not affected by TimerClockDivisor. The frequency of the last 4 clocks can be

further adjusted by TimerClockDivisor, but when using these clocks Counter0 is not available. When Counter0 is not available, it

does not use an external FIO/EIO pin. The divisor has a range of 0-255, where 0 corresponds to a division of 256.

Note that the DACs (Section 2.7) are derived from PWM signals that are affected by the timer clock frequency. The default timer

clock frequency of the U3 is set to 48 MHz, as this results in the minimum DAC output noise. If the frequency is lowered, the DACs

will have more noise, where the frequency of the noise is the timer clock frequency divided by 216.

2.9.1 - Timer Mode Descriptions

2.9.1.1 - PWM Output (16-Bit, Mode 0)

Outputs a pulse width modulated rectangular wave output. Value passed should be 0-65535, and determines what portion of the

total time is spent low (out of 65536 total increments). That means the duty cycle can be varied from 100% (0 out of 65536 are low)

to 0.0015% (65535 out of 65536 are low).

The overall frequency of the PWM output is the clock frequency specified by TimerClockBase/TimerClockDivisor divided by 216.

The following table shows the range of available PWM frequencies based on timer clock settings.

PWM16 Frequency Ranges

TimerClockBase

Divisor=1

Divisor=256

4 MHz

61.04

N/A

12 MHz

183.11

N/A

48 MHz (default)

732.42

N/A

1 MHz /Divisor

15.26

0.06

4 MHz /Divisor

61.04

0.238

12 MHz /Divisor

183.11

0.715

48 MHz /Divisor

732.42

2.861

Table 2.9.1.1-1. 16-bit PWM Frequencies

Note that the clocks above apply to the U3 hardware revision 1.21. With hardware revision 1.20 all clocks are half of those values.

The same clock applies to all timers, so all 16-bit PWM channels will have the same frequency and will have their falling edges at

the same time.

PWM output starts by setting the digital line to output-low for the specified amount of time. The output does not necessarily start

instantly, but rather waits for the internal clock to roll. For example, if the PWM frequency is 100 Hz, that means the period is 10

milliseconds, and thus after the command is received by the device it could be anywhere from 0 to 10 milliseconds before the start

of the PWM output.

If a duty cycle of 0.0% (totally off) is required, consider using a simple inverter IC such as the CD74ACT540E from TI. Or you can

switch the mode of the timer to some input mode, and add an external pull-down to hold the line low when set to input.

2.9.1.2 - PWM Output (8-Bit, Mode 1)

Outputs a pulse width modulated rectangular wave output. Value passed should be 0-65535, and determines what portion of the

total time is spent low (out of 65536 total increments). The lower byte is actually ignored since this is 8-bit PWM. That means the

duty cycle can be varied from 100% (0 out of 65536 are low) to 0.4% (65280 out of 65536 are low).

The overall frequency of the PWM output is the clock frequency specified by TimerClockBase/TimerClockDivisor divided by 28.

The following table shows the range of available PWM frequencies based on timer clock settings.

PWM8 Frequency Ranges

TimerClockBase

Divisor=1

Divisor=256

4 MHz

15625

N/A

12 MHz

46875

N/A

48 MHz (default)

187500

N/A

1 MHz /Divisor

3906.25

15.259

4 MHz /Divisor

15625

61.035

12 MHz /Divisor

46875

183.105

48 MHz /Divisor

187500

732.422

Table 2.9.1.2-1. 8-bit PWM Frequencies

Note that the clocks above apply to the U3 hardware revision 1.21. With hardware revision 1.20 all clocks are half of those values.

The same clock applies to all timers, so all 8-bit PWM channels will have the same frequency and will have their falling edges at

the same time.

PWM output starts by setting the digital line to output-low for the specified amount of time. The output does not necessarily start

instantly, but rather waits for the internal clock to roll. For example, if the PWM frequency is 100 Hz, that means the period is 10

milliseconds, and thus after the command is received by the device it could be anywhere from 0 to 10 milliseconds before the start

of the PWM output.

If a duty cycle of 0.0% (totally off) is required, consider using a simple inverter IC such as the CD74ACT540E from TI. Or you can

switch the mode of the timer to some input mode, and add an external pull-down to hold the line low when set to input.

2.9.1.3 - Period Measurement (32-Bit, Modes 2 & 3)

Mode 2: On every rising edge seen by the external pin, this mode records the number of clock cycles (clock frequency determined

by TimerClockBase/TimerClockDivisor) between this rising edge and the previous rising edge. The value is updated on every

rising edge, so a read returns the time between the most recent pair of rising edges.

In this 32-bit mode, the processor must jump to an interrupt service routine to record the time, so small errors can occur if another

interrupt is already in progress. The possible error sources are:

Other edge interrupt timer modes (2/3/4/5/8/9/12/13). If an interrupt is already being handled due to an edge on the other

timer, delays of a few microseconds are possible.

If a stream is in progress, every sample is acquired in a high-priority interrupt. These interrupts could cause delays on the

order of 10 microseconds.

The always active U3 system timer causes an interrupt 61 times per second. If this interrupt happens to be in progress when

the edge occurs, a delay of about 1 microsecond is possible. If the software watchdog is enabled, the system timer interrupt

takes longer to execute and a delay of a few microseconds is possible.

Note that the minimum measurable period is limited by the edge rate limit discussed in Section 2.9.2.

See Section 3.2.1 for a special condition if stream mode is used to acquire timer data in this mode.

Writing a value of zero to the timer performs a reset. After reset, a read of the timer value will return zero until a new edge is

detected. If a timer is reset and read in the same function call, the read returns the value just before the reset.

Mode 3 is the same except that falling edges are used instead of rising edges.

2.9.1.4 - Duty Cycle Measurement (Mode 4)

Records the high and low time of a signal on the external pin, which provides the duty cycle, pulse width, and period of the signal.

Returns 4 bytes, where the first two bytes (least significant word or LSW) are a 16-bit value representing the number of clock ticks

during the high signal, and the second two bytes (most significant word or MSW) are a 16-bit value representing the number of

clock ticks during the low signal. The clock frequency is determined by TimerClockBase/TimerClockDivisor.

The appropriate value is updated on every edge, so a read returns the most recent high/low times. Note that a duty cycle of 0% or

100% does not have any edges.

To select a clock frequency, consider the longest expected high or low time, and set the clock frequency such that the 16-bit

registers will not overflow.

Note that the minimum measurable high/low time is limited by the edge rate limit discussed in Section 2.9.2.

When using the LabJackUD driver the value returned is the entire 32-bit value. To determine the high and low time this value

should be split into a high and low word. One way to do this is to do a modulus divide by 216 to determine the LSW, and a normal

divide by 216 (keep the quotient and discard the remainder) to determine the MSW.

Writing a value of zero to the timer performs a reset. After reset, a read of the timer value will return zero until a new edge is

detected. If a timer is reset and read in the same function call, the read returns the value just before the reset. The duty cycle reset

is special, in that if the signal is low at the time of reset, the high-time/low-time registers are set to 0/65535, but if the signal is high

at the time of reset, the high-time/low-time registers are set to 65535/0. Thus if no edges occur before the next read, it is possible

to tell if the duty cycle is 0% or 100%.

2.9.1.5 - Firmware Counter Input (Mode 5)

On every rising edge seen by the external pin, this mode increments a 32-bit register. Unlike the pure hardware counters, these

timer counters require that the firmware jump to an interrupt service routine on each edge.

Writing a value of zero to the timer performs a reset. After reset, a read of the timer value will return zero until a new edge is

detected. If a timer is reset and read in the same function call, the read returns the value just before the reset.

2.9.1.6 - Firmware Counter Input With Debounce (Mode 6)

Intended for frequencies less than 10 Hz, this mode adds a debounce feature to the firmware counter, which is particularly useful

for signals from mechanical switches. On every applicable edge seen by the external pin, this mode increments a 32-bit register.

Unlike the pure hardware counters, these timer counters require that the firmware jump to an interrupt service routine on each

edge.

The debounce period is set by writing the timer value. The low byte of the timer value is a number from 0-255 that specifies a

debounce period in 16 ms increments (plus an extra 0-16 ms of variability):

Debounce Period = (0-16 ms) + (TimerValue * 16 ms)

In the high byte (bits 8-16) of the timer value, bit 0 determines whether negative edges (bit 0 clear) or positive edges (bit 0 set) are

counted.

Assume this mode is enabled with a value of 1, meaning that the debounce period is 16-32 ms and negative edges will be

counted. When the input detects a negative edge, it increments the count by 1, and then waits 16-32 ms before re-arming the edge

detector. Any negative edges within the debounce period are ignored. This is good behavior for a normally-high signal where the

switch closure causes a brief low signal (Figure 2-10). The debounce period can be set long enough so that bouncing on both the

switch closure and switch open is ignored.

Writing a value of zero to the timer performs a reset. After reset, a read of the timer value will return zero until a new edge is

detected. If a timer is reset and read in the same function call, the read returns the value just before the reset.

2.9.1.7 - Frequency Output (Mode 7)

Outputs a square wave at a frequency determined by TimerClockBase/TimerClockDivisor divided by 2*Timer#Value. The Value

passed should be between 0-255, where 0 is a divisor of 256. By changing the clock configuration and timer value, a wide range

of frequencies can be output, as shown in the following table:

Mode 7 Frequency Ranges

Divisor=1

TimerClockBase

Value=1

Value=256

4 MHz

2000000

7812.5

12 MHz

6000000

23437.5

48 MHz (default)

24000000

93750

Divisor=1

Divisor=256

Value=1

Value=256

1 MHz /Divisor

500000

7.629

4 MHz /Divisor

2000000

30.518

12 MHz /Divisor

6000000

91.553

48 MHz /Divisor

24000000

366.211

Table 2.9.1.7-1. Mode 7 Frequency Ranges

Note that the clocks above apply to the U3 hardware revision 1.21. With hardware revision 1.20 all clocks are half of those values.

The frequency output has a -3 dB frequency of about 10 MHz on the FIO lines. Accordingly, at high frequencies the output

waveform will get less square and the amplitude will decrease.

The output does not necessarily start instantly, but rather waits for the internal clock to roll. For example, if the output frequency is

100 Hz, that means the period is 10 milliseconds, and thus after the command is received by the device it could be anywhere from

0 to 10 milliseconds before the start of the frequency output.

Frequency List for U3 Timer Mode 7

CSV list of the 262,144 possible frequency output options on the U3 hardware rev 1.21+. Columns are Hz, base clock, clock

divisor, and timer value. Oct 27, 2008.

File attachment:

U3_FreqOutList_Hz_Base_Divisor_Value.csv

2.9.1.8 - Quadrature Input (Mode 8)

Requires both timers, where Timer0 will be quadrature channel A, and Timer1 will be quadrature channel B. The U3 does 4x

quadrature counting, and returns the current count as a signed 32-bit integer (2’s complement). The same current count is returned

on both timer value parameters.

Writing a value of zero to either or both timers performs a reset of both. After reset, a read of either timer value will return zero until

a new quadrature count is detected. If a timer is reset and read in the same function call, the read returns the value just before the

reset.

4X Counting

Quadrature mode uses the very common 4X counting method, which provides the highest resolution possible. That means you get

a count for every edge (rising & falling) on both phases (A & B). Thus if you have an encoder that provides 32 PPR, and you rotate

that encoder forward 1 turn, the timer Value register will be incremented by +128 counts.

Z-phase support

Quadrature mode supports Z-Phase. When enabled this feature will set the count to zero when the specified IO line sees a logic

high.

Z-phase is controlled by the value written to the timer during initialization. To enable z-phase support set bit 15 to 1 and set bits 0

through 4 to the DIO number that Z is connected to. EG: for a Z-line on EIO3 set the timer value to 0x800B or 32779. This value

should be sent to both the A and B timers.

Note that the LabJack will only check Z when it sees an edge on A or B.

Z-phase support requires Firmware 1.30 or later.

2's Complement

Other timer modes return unsigned values, but this timer mode is unique in that it returns a signed value from -2147483648 to

+2147483647. That is, a 32-bit 2's complement value. When you do a timer value read and get back a single float from the UD

driver, the math is already done and you get back a value from -2147483648.0 to +2147483647.0, but when using the special

channels 20x/23x/224 you get the LSW and MSW separately and have to do the math yourself. Search for 2's complement math

for your particular programming language.

In a language such as C++, you start by doing using unsigned 32-bit variables & constants to compute Value = (MSW * 65536) +

LSW. Then simply cast Value to a signed 32-bit integer.

In a language such as Java that does not support unsigned integers, do everything with signed 64-bit variables & constants. First

calculate Value = (MSW * 65536) + LSW. If Value < 2147483648, you are done. If Value >= 2147483648, do ActualValue = -1 *

(4294967296 - Value).

2.9.1.9 - Timer Stop Input (Mode 9)

This mode should only be assigned to Timer1. On every rising edge seen by the external pin, this mode increments a 16-bit

register. When that register matches the specified timer value (stop count value), Timer0 is stopped. The range for the stop count

value is 1-65535. Generally, the signal applied to Timer1 is from Timer0, which is configured in some output timer mode. One

place where this might be useful is for stepper motors, allowing control over a certain number of steps.

Note that the timer is counting from the external pin like other input timer modes, so you must connect something to the stop timer

input pin. For example, if you are using Timer1 to stop Timer0 which is outputting pulses, you must connect a jumper from Timer0

to Timer1.

Once this timer reaches the specified stop count value, and stops the adjacent timer, the timers must be reconfigured to restart the

output.

When Timer0 is stopped, it is still enabled but just not outputting anything. Thus rather than returning to whatever previous digital

I/O state was on that terminal, it goes to the state "digital-input" (which has a 100 kΩ pull-up to 3.3 volts). That means the best

results are generally obtained if the terminal used by Timer0 was initially configured as digital input (factory default), rather than

output-high or output-low. This will result in negative going pulses, so if you need positive going pulses consider using a simple

inverter IC such as the CD74ACT540E from TI.

The MSW of the read from this timer mode returns the number of edges counted, but does not increment past the stop count value.

The LSW of the read returns edges waiting for.

2.9.1.10 - System Timer Low/High Read (Modes 10 & 11)

The LabJack U3 has a free-running internal 64-bit system timer with a frequency of 4 MHz. Timer modes 10 & 11 return the lower

or upper 32-bits of this timer. An FIO line is allocated for these modes like normal, even though they are internal readings and do

not require any external connections. This system timer cannot be reset, and is not affected by the timer clock.

If using both modes 10 & 11, read both in the same low-level command and read 10 before 11.

Mode 11, the upper 32 bits of the system timer, is not available for stream reads. Note that when streaming on the U3, the timing is

known anyway (elapsed time = scan rate * scan number) and it does not make sense to stream the system timer modes 10 or 11.

Note that system timer runs at 2MHz on U3 hardware 1.20.

2.9.1.11 - Period Measurement (16-Bit, Modes 12 & 13)

Similar to the 32-bit edge-to-edge timing modes described above (modes 2 & 3), except that hardware capture registers are

used to record the edge times. This limits the times to 16-bit values, but is accurate to the resolution of the clock, and not subject to

any errors due to firmware processing delays.

Note that the minimum measurable period is limited by the edge rate limit discussed in Section 2.9.2.

2.9.1.12 - Line-to-Line Measurement (Mode 14)

This timer mode requires firmware 1.30 or later.

Introduction:

The Line-to-Line timer mode uses two timers to measure the time between specified edges on two different lines. For instance,

you can measure the time between a rising edge on Timer0 and a falling edge on Timer1. When the LabJack sees the specified

edge on Timer0 it starts counting until it sees the specified edge on Timer1. High resolution up to 20.8ns can be achieved with this

mode.

Configuring:

To configure a LabJack for Line-to-Line mode set an even timer and the next (odd) timer to mode 14. The timer values determine

the edge that the timer will respond to, 1 being rising, 0 being falling. So, if Timer0's value is 0 and Timer1's is 1 then the LabJack

will measure the time between a falling edge on Timer0 to a rising edge on Timer1.

Readings:

Once configured the timer will return zero until both specified edges have been detected. The time difference in TimerClock

periods is then returned by both timers until they are reset. Both timers will return the same reading, so it is only necessary to read

one or the other. To convert to time, divide the value returned by the timer clock. This mode returns 16-bit values, so care should be

taken to be sure that the specified condition does not exceed the maximum time. The maximum time can be calculated by (2^16-

1)/TimerClock.

Resetting:

Once a measurement has been acquired the even timer needs to be reset before the LabJack will measure again. Values

specified when resetting have no effect. Once reset the even timer will return zero until a new measurement has been completed.

Resetting the odd timer is optional, if not reset it will continue to return the last measurement until a new one has been completed.

2.9.1.12 - Line-to-Line (Mode 14)

2.9.2 - Timer Operation/Performance Notes

Note that the specified timer clock frequency is the same for all timers. That is, TimerClockBase and TimerClockDivisor are

singular values that apply to all timers. Modes 0, 1, 2, 3, 4, 7, 12, and 13, all are affected by the clock frequency, and thus the

simultaneous use of these modes has limited flexibility. This is often not an issue for modes 2 and 3 since they use 32-bit

registers.

The output timer modes (0, 1, and 7) are handled totally by hardware. Once started, no processing resources are used and other

U3 operations do not affect the output.

The edge-detecting timer input modes do require U3 processing resources, as an interrupt is required to handle each edge. Timer

modes 2, 3, 5, 6, 9, 12, and 13 must process every applicable edge (rising or falling). Timer modes 4 and 8 must process every

edge (rising and falling). To avoid missing counts, keep the total number of processed edges (all timers) less than 30,000 per

second (hardware V1.21). That means that in the case of a single timer, there should be no more than 1 edge per 33 μs. For

multiple timers, all can process an edge simultaneously, but if for instance both timers get an edge at the same time, 66 μs should

be allowed before any further edges are applied. If streaming is occurring at the same time, the maximum edge rate will be less

(7,000 per second), and since each edge requires processing time the sustainable stream rates can also be reduced.

2.10 - SPC (… and SCL/SDA/SCA)

The SPC terminal is used for manually resetting default values or jumping in/out of flash programming mode.

Hardware revision 1.20 and 1.21, had terminals labeled SCL, SDA, and/or SCA. On revision 1.20, these terminals did nothing

except that SCL is used for the SPC functionality described above. On revision 1.21, these terminals were used for asynchronous

functionality, and SCL is used for the SPC functionality described above. Note that these terminals never have anything to do with

I²C.

2.11 - DB15

The DB15 connector brings out 12 additional I/O. It has the potential to be used as an expansion bus, where the 8 EIO are data

lines and the 4 CIO are control lines. The EIO are flexible I/O as described in Section 2.5, so can be used as digital input, digital,

output, analog input, timer, or counter.

In the Windows LabJackUD driver, the EIO are addressed as digital I/O bits 8 through 15, and the CIO are addressed as bits 16-

19.

0-7 FIO0-FIO7

8-15 EIO0-EIO7

16-19 CIO0-CIO3

These 12 channels include an internal series resistor that provides overvoltage/short-circuit protection. These series resistors also

limit the ability of these lines to sink or source current. Refer to the specifications in Appendix A.

All digital I/O on the U3 have 3 possible states: input, output-high, or output-low. Each bit of I/O can be configured individually.

When configured as an input, a bit has a ~100 kO pull-up resistor to 3.3 volts. When configured as output-high, a bit is connected

to the internal 3.3 volt supply (through a series resistor). When configured as output-low, a bit is connected to GND (through a

series resistor).

DB15 Pinouts

CIO0

CIO1

CIO2

CIO3

GND

EIO0

EIO1

EIO2

EIO3

EIO4

EIO5

EIO6

EIO7

GND

Table 2.11-1. DB15 Connector Pinouts

The above image shows standard DB15 pin numbers looking into the female connector on the U3.

2.11.1 - CB15 Terminal Board

The CB15 terminal board connects to the LabJack U3’s DB15 connector. It provides convenient screw terminal access to the 12

digital I/O available on the DB15 connector. The CB15 is designed to connect directly to the LabJack, or can connect via a

standard 15-line 1:1 male-female DB15 cable.

2.11.2 - RB12 Relay Board

The RB12 relay board provides a convenient interface for the U3 to industry standard digital I/O modules, allowing electricians,

engineers, and other qualified individuals, to interface a LabJack with high voltages/currents. The RB12 relay board connects to

the DB15 connector on the LabJack, using the 12 EIO/CIO lines to control up to 12 I/O modules. Output or input types of digital I/O

modules can be used. The RB12 is designed to accept G4 series digital I/O modules from Opto22, and compatible modules from

other manufacturers such as the G5 series from Grayhill. Output modules are available with voltage ratings up to 200 VDC or 280

VAC, and current ratings up to 3.5 amps.

2.12 - U3-OEM

There is an OEM version of the U3 available (-LV and -HV). It is a board only (no enclosure, no screwdriver, no cable), and does

not have most of the through-hole components installed. The picture below shows how the U3-OEM ships by default. Leaving the

through-hole parts off makes the OEM board very flexible. Many applications do not need the through-hole parts, but if needed they

are much easier to install than uninstall.

This manual suits for next models

Table of contents

Popular I/O System manuals by other brands

ICP DAS USA

ICP DAS USA IR-210 quick start

Black Box

Black Box IC909C manual

Pilz

Pilz PSSu E F BSW operating manual

HomeMatic

HomeMatic HmIPW-FIO6 Installation instructions and operating manual

WAGO

WAGO I/O System 750 XTR 750-495/040-010 manual

National Instruments

National Instruments NI 9231 Getting started guide

GMI

GMI D5293S instruction manual

NI FieldPoint FP-AIO-600 operating instructions

Bürkert

Bürkert 8643 PA Operating instruction

ICP DAS USA

ICP DAS USA ISaGRAF VP-2117 Getting started

M-system

M-system R3-PD16C instruction manual

ADLINK Technology

ADLINK Technology PCIe-7300A user manual

Weidmuller

Weidmuller WI-I/O 9-K user manual

Moxa Technologies

Moxa Technologies ioLogik 2500 Series Quick installation guide

WAGO

WAGO I/O SYSTEM 750 quick start

turck

turck excom EG-VA655526/113-0200/134 quick start guide

Tews Technologies

Tews Technologies TPMC671 user manual

NI 9228 Getting started guide

LabJack LJU3-LV User manual

Popular I/O System manuals by other brands