Measurement Computing USB-1208FS User Manual

USB-1208FS

Analog and Digital I/O

User's Guide

Document Revision 6, March, 2010

© Copyright 2010, Measurement Computing Corporation

HM USB-1208FS.doc

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3

USB-1208FS User's Guide

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4

Table of Contents

Preface

About this User's Guide ....................................................................................................................... 7

What you will learn from this user's guide ......................................................................................................... 7

Conventions in this user's guide ......................................................................................................................... 7

Where to find more information ......................................................................................................................... 7

Chapter 1

Introducing the USB-1208FS................................................................................................................ 8

USB-1208FS block diagram ............................................................................................................................... 9

Software features ................................................................................................................................................ 9

Connecting a USB-1208FS to your computer is easy....................................................................................... 10

Chapter 2

Installing the USB-1208FS .................................................................................................................. 11

What comes with your USB-1208FS shipment? .............................................................................................. 11

Hardware .........................................................................................................................................................................11

Additional documentation ................................................................................................................................................11

Unpacking the USB-1208FS ............................................................................................................................ 11

Installing the software ...................................................................................................................................... 12

Installing the hardware ..................................................................................................................................... 12

Chapter 3

Functional Details ............................................................................................................................... 13

Theory of operation - analog input acquisition modes ..................................................................................... 13

Software paced mode .......................................................................................................................................................13

Continuous scan mode .....................................................................................................................................................13

External components ........................................................................................................................................ 13

USB connector .................................................................................................................................................................14

LED .................................................................................................................................................................................14

Screw terminal wiring ......................................................................................................................................................14

Main connector and pin out .............................................................................................................................................15

Analog input terminals (CH0 IN - CH7 IN).....................................................................................................................15

Analog output terminals (D/A OUT 0 and D/A OUT 1) ................................................................ ..................................18

Digital I/O terminals (Port A0 to A7, and Port B0 to B7) ................................................................................................18

Power terminals ...............................................................................................................................................................19

Calibration terminal .........................................................................................................................................................19

Ground terminals .............................................................................................................................................................20

External trigger terminal ..................................................................................................................................................20

SYNC terminal ................................................................................................................................................................20

Counter terminal ..............................................................................................................................................................20

Accuracy ........................................................................................................................................................... 20

USB-1208FS channel gain queue feature ......................................................................................................... 23

Synchronizing multiple units ............................................................................................................................ 23

Chapter 4

Specifications ...................................................................................................................................... 25

Analog input ..................................................................................................................................................... 25

Analog output ................................................................................................................................................... 27

Digital input/output........................................................................................................................................... 27

External trigger ................................................................................................................................................. 28

External clock input/output............................................................................................................................... 28

Counter ............................................................................................................................................................. 29

Non-volatile memory ........................................................................................................................................ 29

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USB-1208FS User's Guide

Microcontroller ................................................................................................................................................. 29

Power ................................................................................................................................................................ 29

General ............................................................................................................................................................. 30

Environmental .................................................................................................................................................. 30

Mechanical ....................................................................................................................................................... 30

Main connector and pin out .............................................................................................................................. 30

4-channel differential mode .............................................................................................................................................31

8-channel single-ended mode ...........................................................................................................................................31

Declaration of Conformity .................................................................................................................. 32

6

Preface

About this User's Guide

What you will learn from this user's guide

This user's guide explains how to install, configure, and use the USB-1208FS so that you get the most out of its
USB data acquisition features.

This user's guide also refers you to related documents available on our web site, and to technical support
resources.

Conventions in this user's guide

For more information on …

Text presented in a box signifies additional information and helpful hints related to the subject matter you are
reading.

Caution! Shaded caution statements present information to help you avoid injuring yourself and others,

damaging your hardware, or losing your data.

< : > Angle brackets that enclose numbers separated by a colon signify a range of numbers, such as those assigned

to registers, bit settings, etc.

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

example:

1. Insert the disk or CD and click the OK button.

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

example:
The InstaCal installation procedure is explained in the Quick Start Guide.
Never touch the exposed pins or circuit connections on the board.

Where to find more information

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

7

Chapter 1

Introducing the USB-1208FS

This user's guide contains all of the information you need to connect the USB-1208FS to your computer and to
the signals you want to measure.

The USB-1208FS is a USB 2.0 full-speed device supported under popular Microsoft® Windows® operating
systems. It is designed for USB 1.1 ports, and was tested for full compatibility with both USB 1.1 and USB 2.0
ports.

The USB-1208FS features eight analog inputs, two 12-bit analog outputs, 16 digital I/O connections, and one
32-bit external event counter. The USB-1208FS is powered by the +5 volt USB supply from your computer. No
external power is required.

The analog inputs are software configurable for either eight 11-bit single-ended inputs, or four 12-bit
differential inputs. Sixteen digital I/O lines are independently selectable as input or output in two 8-bit ports.

A 32-bit counter can count TTL pulses. The counter increments when the TTL levels transition from low to
high (rising-edge).

A SYNC (synchronization) input / output line lets you pace the analog input acquisition of one USB module
from the clock output of another.

The USB-1208FS is shown in Figure 1. I/O connections are made to the screw terminals located along each side
of the USB-1208FS.

Figure 1. USB-1208FS

8

USB-1208FS User's Guide Introducing the USB-1208FS

USB-1208FS block diagram

USB-1208FS functions are illustrated in the block diagram shown here.

Figure 2. USB-1208FS functional block diagram

Software features

For information on the features of InstaCal and the other software included with your USB-1208FS, refer to the
Quick Start Guide that shipped with your device.

9

USB-1208FS User's Guide Introducing the USB-1208FS

Connecting a USB-1208FS to your computer is easy

Installing a data acquisition device has never been easier.
 The USB-1208FS relies upon the Microsoft Human Interface Device (HID) class drivers. The HID class

drivers ship with every copy of Windows that is designed to work with USB ports. We use the Microsoft
HID because it is a standard, and its performance delivers full control and maximizes data transfer rates for
your USB-1208FS. No third-party device driver is required.

 The USB-1208FS is plug-and-play. There are no jumpers to position, DIP switches to set, or interrupts to

configure.

 You can connect the USB-1208FS before or after you install the software, and without powering down

your computer first. When you connect an HID to your system, your computer automatically detects it and
configures the necessary software. You can connect and power multiple HID peripherals to your system
using a USB hub.

You can run up to two USB-1208FS units on most computers.

 You can connect your system to various devices using a standard four-wire cable. The USB connector

replaces the serial and parallel port connectors with one standardized plug and port combination.

 You do not need a separate power supply module. The USB automatically delivers the electrical power

required by each peripheral connected to your system.

 Data can flow two ways between a computer and peripheral over USB connections.

10

Installing the USB-1208FS

What comes with your USB-1208FS shipment?

As you unpack your USB-1208FS, verify that the following components are included.

Hardware

 USB-1208FS (shown with cable)

Chapter 2

 USB cable (2 meter length)

Additional documentation

In addition to this hardware user's guide, you should also receive the Quick Start Guide (available in PDF at

the software you received with your USB-1208FS and information regarding installation of that software.
Please read this booklet completely before installing any software or hardware.

Unpacking the USB-1208FS

As with any electronic device, you should take care while handling to avoid damage from static
electricity. Before removing the USB-1208FS from its packaging, ground yourself using a wrist strap or by
simply touching the computer chassis or other grounded object to eliminate any stored static charge.

If any components are missing or damaged, notify Measurement Computing Corporation immediately by
phone, fax, or e-mail:

 Phone: [phone] and follow the instructions for reaching Tech Support.
 Fax: [phone] to the attention of Tech Support
 Email: [e-mail]

11

USB-1208FS User's Guide Installing the USB-1208FS

Installing the software

Quick-Start.pdf.

Installing the hardware

Be sure you are using the latest system software

Before you install your USB-1208FS, run Windows Update to update your operating system with the latest HID
and USB drivers.

To connect the USB-1208FS to your system, turn your computer on, and connect the USB cable to a USB port
on your computer or to an external USB hub that is connected to your computer. The USB cable provides power
and communication to the USB-1208FS.

When you connect the USB-1208FS for the first time, a series of Found New Hardware popup balloons
(Windows XP) or dialogs (other Windows versions) opens as the USB-1208FS is detected by your computer.

It is normal for multiple dialogs to open when you connect the USB-1208FS for the first time. The last popup
balloon or dialog states "Your new hardware is installed and ready to use," and the LED on the USB-1208FS
should flash and then remain lit. This indicates that communication is established between the USB-1208FS and
your computer.

You can install up to two USB-1208FS units on most computers. If you need to connect more than two USB­1208FS units to your computer, contact Tech Support by phone, fax, or e-mail:

 Phone: [phone] and follow the instructions for reaching Tech Support.
 Fax: [phone] to the attention of Tech Support
 Email: [e-mail]

Caution! Do not disconnect any device from the USB bus while the computer is communicating with the

USB-1208FS, or you may lose data and/or your ability to communicate with the USB-1208FS.

If the LED turns off

If the LED is illuminated but then turns off, the computer has lost communication with the USB-1208FS. To
restore communication, disconnect the USB cable from the computer, and then reconnect it. This should restore
communication, and the LED should turn back on.

12

Chapter 3

Functional Details

Theory of operation - analog input acquisition modes

The USB-1208FS can acquire analog input data in two different modes – software paced and continuous scan.

Maximum throughput is system-dependent

Maximum throughput may be lower in Windows operating systems that predate Windows XP.

Software paced mode

In software paced mode, you can acquire one analog sample at a time. You initiate the A/D conversion by
calling a software command. The analog value is converted to digital and returned to the computer. You can
repeat this procedure until you have the total number of samples that you want from one channel.

The maximum throughput sample rate in software paced mode is system-dependent.

Continuous scan mode

In continuous scan mode, you can acquire data from up to eight channels. The analog data is continuously
acquired and converted to digital values until you stop the scan. Data is transferred in blocks of 31 samples from
the USB-1208FS to the memory buffer on your computer.

The maximum continuous scan rate of 50 kS/s is an aggregate rate. The total acquisition rate for all channels
cannot exceed 50 kS/s. You can acquire data from one channel at 50 kS/s, two channels at 25 kS/s, and four
channels at 12.5 kS/s. You can start a continuous scan with either a software command or with an external
hardware trigger event.

External components

The USB-1208FS has the following external components, as shown in Figure 3.

 USB connector
 LED
 Screw terminal banks (2)

Figure 3. USB-1208FS external components

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USB-1208FS User's Guide Functional Details

LED Illumination

Indication

Steady green

The USB-1208FS is connected to a computer or external USB hub.

Blinks continuously

Data is being transferred.

USB connector

The USB connector is on the right side of the USB-1208FS. This connector provides +5 V power and
communication. The voltage supplied through the USB connector is system-dependent, and may be less than
5 V. No external power supply is required.

LED

The LED on the front of the housing indicates the communication status of the USB-1208FS. It uses up to 5 mA
of current and cannot be disabled. The table below defines the function of the USB-1208FS LED.

LED Illumination

Screw terminal wiring

The USB-1208FS has two rows of screw terminals—one row on the top edge of the housing, and one row on
the bottom edge. Each row has 20 connections. Pin numbers are identified in Figure 4.

Figure 4. USB-1208FS Screw terminal pin numbers

Screw terminal – pins 1-20

The screw terminals on the top edge of the USB-1208FS (pins 1 to 20) provide the following connections:

 Eight analog input connections (CH0 IN to CH7 IN)
 Two analog output connections (D/A OUT 0 to D/A OUT 1)
 One external trigger source (TRIG_IN)
 One SYNC terminal for external clocking and multi-unit synchronization (SYNC)
 One calibration terminal (CAL)
 Five analog ground connections (AGND)
 One ground connection (GND)
 One external event counter connection (CTR)

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USB-1208FS User's Guide Functional Details

Connector type

Screw terminal

Wire gauge range

16 AWG to 30 AWG

8-channel single-ended mode pin out

4-channel differential mode pin out

Screw terminal – pins 21-40

The screw terminals on the bottom edge of the (pins 21 to 40) provide the following connections:

 16 digital I/O connections (PortA0 to Port A7, and Port B0 to Port B7)
 One power connection (PC+5 V)
 Three ground connections (GND)

Main connector and pin out

Analog input terminals (CH0 IN - CH7 IN)

You can connect up to eight analog input connections to the screw terminal containing pins 1 to 20 (CH0 IN
through CH7 IN.) Refer to the pinout diagrams above for the location of these pins.

You can configure the analog input channels as eight single-ended channels or four differential channels. When
configured for differential mode, each analog input has 12-bit resolution. When configured for single-ended
mode, each analog input has 11-bit resolution, due to restrictions imposed by the A/D converter.

Single-ended configuration

When all of the analog input channels are configured for single-ended input mode, eight analog channels are
available. The input signal is referenced to signal ground (GND), and delivered through two wires:

 The wire carrying the signal to be measured connects to CH# IN.
 The second wire connects to AGND.

The input range for single-ended mode is ±10 V. No other ranges are supported in single-ended mode. Figure 5
illustrates a typical single-ended measurement connection.

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USB-1208FS User's Guide Functional Details

Figure 5. Single-ended measurement connection

Battery voltage should read as expected when the hardware is configured for single-ended mode.

Single-ended measurements using differential channels

To perform a single-ended measurement using differential channels, connect the signal to "CHn IN HI" input,
and ground the associated "CHn IN LO" input.

Differential configuration

When all of the analog input channels are configured for differential input mode, four analog channels are
available. In differential mode, the input signal is measured with respect to the low input.

The input signal is delivered through three wires:
 The wire carrying the signal to be measured connects to CH0 IN HI, CH1 IN HI, CH2 IN HI, or

CH3 IN HI.

 The wire carrying the reference signal connects to CH0 IN LO, CH1 IN LO, CH2 IN LO, or

CH3 IN LO.

 The third wire connects to GND.
A low-noise precision programmable gain amplifier (PGA) is available on differential channels to provide gains

of up to 20 and a dynamic range of up to 12-bits. Differential mode input voltage ranges are ±20 V, ±10 V,
±5 V, ±4 V, ±2.5 V, ±2.0 V, ±1.25 V, and ±1.0 V.

In differential mode, the following two requirements must be met for linear operation:

 Any analog input must remain in the −10V to +20V range with respect to ground at all times.
 The maximum differential voltage on any given analog input pair must remain within the selected voltage

range.

The input [common-mode voltage + signal] of the differential channel must be in the −10 V to +20 V range in
order to yield a useful result. For example, you input a 4 V pp sine wave to CHHI, and apply the same sine
wave 180° out of phase to CHLO. The common mode voltage is 0 V. The differential input voltage swings from
4 V-(-4 V) = 8 V to -4 V-4 V = -8V. Both inputs satisfy the -10 V to +20 V input range requirement, and the
differential voltage is suited for the ±10 V input range (see Figure 6).

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USB-1208FS User's Guide Functional Details

Figure 6. Differential voltage example: common mode voltage of 0 V

If you increase the common mode voltage to 11 V, the differential remains at ±8 V. Although the [common­mode voltage + signal] on each input now has a range of +7 V to +15 V, both inputs still satisfy the -10 V to

+20 V input requirement (see Figure 7).

Figure 7. Differential voltage example: common mode voltage of 11 V

If you decrease the common-mode voltage to -7 V, the differential stays at ±8 V. However, the solution now
violates the input range condition of -10 V to +20 V. The voltage on each analog input now swings from -3 V to

-11 V. Voltages between -10 V and -3 V are resolved, but those below -10 V are clipped (see Figure 8).

Figure 8. Differential voltage example: common mode voltage of -7 V

Since the analog inputs are restricted to a −10 V to +20 V signal swing with respect to ground, all ranges except
±20V can realize a linear output for any differential signal with zero common mode voltage and full scale signal
inputs. The ±20 V range is the exception. You cannot put −20 V on CHHI and 0 V on CHLO since this violates
the input range criteria.

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USB-1208FS User's Guide Functional Details

CHHI

CHLO

Result

-20 V

0 V

In Valid

-15 V

+5 V

In Valid

-10 V

0 V

-10 V

-10 V

+10 V

-20 V

0 V

+10 V

-10 V

0 V

+20 V

-20 V

+10 V

-10 V

+20 V

+10 V

0 V

+10 V

+15 V

-5 V

+20 V

+20 V

0

+20 V

The table below shows some possible inputs and the expected results.

Sample inputs and differential results

For more information on analog signal connections

For more information on single-ended and differential inputs, refer to the Guide to Signal Connections (this
document is available on our web site at www.mccdaq.com/signals/signals.pdf)

Analog output terminals (D/A OUT 0 and D/A OUT 1)

You can connect up to two analog output connections to the screw terminal pins 13 and 14 (D/A OUT 0 and D/A

OUT 1). Refer to the pinout diagrams on page 15 for the location of these pins.

Each channel can be paced individually at rates up to 10,000 updates per second. Both channels can be paced
simultaneously using the same time base at 5000 updates per channel. The 0-4.096 V output range provides a
convenient 1 mV per LSB when setting the output voltage levels.

Digital I/O terminals (Port A0 to A7, and Port B0 to B7)

You can connect up to 16 digital I/O lines to the screw terminal containing pins 21 to 40 (Port A0 to Port A7,
and Port B0 to Port B7.) Refer to the pinout diagrams on page 15 for the location of these pins. You can
configure each digital port for either input or output.

When you configure the digital bits for input, you can use the digital I/O terminals to detect the state of any
TTL level input. Refer to the switch shown in Figure 9 and the schematic shown in Figure 10. If the switch is
set to the +5 V input, Port A0 reads TRUE (1). If you move the switch to GND, Port A0 reads FALSE.

Figure 9. Digital connection Port A0 detecting the state of a switch

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USB-1208FS User's Guide Functional Details

Figure 10. Schematic showing switch detection by digital channel Port A0

For more information on digital signal connections

For more information on digital signal connections and digital I/O techniques, refer to the Guide to Signal
Connections (available on our web site at www.mccdaq.com/signals/signals.pdf).

Power terminals

The PC +5V connection (pin 30) is on the bottom screw terminal of the USB-1208FS. Refer to the pinout

diagrams on page 15 for the location of this pin. This terminal draws power from the USB connector. The +5 V

screw terminal is a 5 volt output that is supplied by the host computer.

Caution! The +5 V terminal is an output. Do not connect to an external power supply or you may damage

the USB-1208FS and possibly the computer.

The maximum total output current that can be drawn from all USB-1208FS connections (power, analog and
digital outputs) is 420 mA. This maximum applies to most personal computers and self-powered USB hubs.
Bus-powered hubs and notebook computers may limit the maximum available output current to 100 mA.

Just connecting the USB-1208FS to your computer draws 80 mA of current from the USB +5 V supply. Once
you start running applications with the USB-1208FS, each DIO bit can draw up to 2.5 mA, and each analog
output can draw 15 mA. The maximum amount of +5 V current available for experimental use, over and above
that required by the USB-1208FS, is the difference between the total current requirement of the USB (based on
the application), and the allowed current draw of the PC platform (500 mA for desktop PCs and self-powered
hubs, or 100 mA for bus-powered hubs and notebook computers).

With all outputs at their maximum output current, you can calculate the total current requirement of the USB­1208FS USB +5 V as follows:

(USB-1208FS @ 80 mA) + (16 DIO @ 2.5 mA ea) + (2 AO @ 15 mA ea ) = 150 mA

For an application running on a PC or powered hub, the maximum available excess current is 500 mA−150 mA
= 350 mA. This number is the total maximum available current at the PC +5 V screw terminals. Measurement
Computing highly recommends that you figure in a safety factor of 20% below this maximum current loading
for your applications. A conservative, safe user maximum in this case would be in the 350-380 mA range.

Since laptop computers typically allow up to 100 mA, the USB-1208FS in a fully-loaded configuration may be
above that allowed by the computer. In this case, you must determine the per-pin loading in the application to
ensure that the maximum loading criteria is met. The per-pin loading is calculated by simply dividing the +5 V
by the load impedance of the pin in question.

Calibration terminal

The CAL connection (pin 16) is an output you should use only to calibrate the USB-1208FS. Refer to the pinout

diagrams on page 15 for the location of this pin. Calibration of the USB-1208FS is software-controlled via

InstaCal.

19

USB-1208FS User's Guide Functional Details

Ground terminals

The four analog ground (AGND) connections provide a common ground for all USB-1208FS input channels.
Four ground (GND) connections provide a common ground for the DIO, TRIG_IN, CTR, SYNC and PC +5V
connections. Refer to the pinout diagrams on page 15 for the location of the AGND and GND terminal pins.

External trigger terminal

The TRIG_IN connection (pin 18) can be configured for either rising or falling edge. Refer to the pinout

diagrams on page 15 for the location of the TRIG_IN terminal pin.

SYNC terminal

The SYNC connection (pin 19) is a bidirectional I/O signal. You can use it for two purposes:
 Configure as an external clock input to externally source the A/D conversions. The SYNC terminal

supports TTL-level input signals of up to 50 kHz.

 Configure as an output to synchronize with a second USB unit and acquire data from 16 channels.
Refer to the pinout diagrams on page 15 for the location of this pin. For more information on synchronizing

multiple units, refer to page 23.

Counter terminal

The CTR connection (pin 20) is input to the 32-bit external event. Refer to the pinout diagrams on page 15 for
the location of this pin. The internal counter increments when the TTL levels transition from low to high. The
counter can count frequencies of up to 1 MHz.

Accuracy

The overall accuracy of any instrument is limited by the error components within the system. Quite often,
resolution is incorrectly used to quantify the performance of a measurement product. While "12-bits" or "1 part
in 4096" does indicate what can be resolved, it provides little insight into the quality of an absolute
measurement. Accuracy specifications describe the actual results that can be realized with a measurement
device.

There are three types of errors which affect the accuracy of a measurement system:

 offset
 gain
 nonlinearity.

The primary error sources in the USB-1208FS are offset and gain. Nonlinearity is small in the USB-1208FS,
and is not significant as an error source with respect to offset and gain.

Figure 11 shows an ideal, error-free, USB-1208FS transfer function. The typical calibrated accuracy of the
USB-1208FS is range-dependent, as explained in the "Specifications" chapter on page 25. We use a ±10 V
range here as an example of what you can expect when performing a measurement in this range.

20

USB-1208FS User's Guide Functional Details

Figure 11. Ideal ADC transfer function

The USB-1208FS offset error is measured at mid-scale. Ideally, a zero volt input should produce an output code
of 2048. Any deviation from this is an offset error. Figure 12 shows the USB-1208FS transfer function with an
offset error. The typical offset error specification on the ±10 V range is ±9.77 mV. Offset error affects all codes
equally by shifting the entire transfer function up or down along the input voltage axis.

The accuracy plots in Figure 12 are drawn for clarity and are not drawn to scale.

Figure 12. ADC transfer function with offset error

Gain error is a change in the slope of the transfer function from the ideal, and is typically expressed as a
percentage of full-scale. Figure 13 shows the USB-1208FS transfer function with gain error. Gain error is easily
converted to voltage by multiplying the full-scale (FS) input by the error.

21

USB-1208FS User's Guide Functional Details

The accuracy plots in Figure 13 are drawn for clarity and are not drawn to scale.

Figure 13. ADC Transfer function with gain error

For example, the USB-1208FS exhibits a typical calibrated gain error of ±0.2% on all ranges. For the ±10 V
range, this would yield 10 V × ±0.002 = ±20 mV. This means that at full scale, neglecting the effect of offset for
the moment, the measurement would be within 20 mV of the actual value. Note that gain error is expressed as a
ratio. Values near ±FS are more affected from an absolute voltage standpoint than are values near mid-scale,
which see little or no voltage error.

Combining these two error sources in Figure 14, we have a plot of the error band of the USB-1208FS for the
±10 V range. This is a graphical version of the typical accuracy specification of the product.

The accuracy plots in Figure 14 are drawn for clarity and are not drawn to scale.

Figure 14. Error band plot

22

USB-1208FS User's Guide Functional Details

Element

Channel

Range

0

CH0

BIP10V

1

CH0

BIP5V

2

CH7

BIP10V

3

CH2

BIP1V

USB-1208FS channel gain queue feature

The USB-1208FS's channel gain queue feature allows you to set up a scan sequence with a unique per-channel
gain setting and channel sequence.

The channel gain queue feature removes the restriction of using an ascending channel sequence at a fixed gain.
This feature creates a channel list which is written to local memory on the USB-1208FS. The channel list is
made up of a channel number and range setting. An example of a four-element list is shown in the table below.

Sample channel gain queue list

When a scan begins with the gain queue enabled, the USB-1208FS reads the first element, sets the appropriate
channel number and range, and then acquires a sample. The properties of the next element are then retrieved,
and another sample is acquired. This sequence continues until all elements in the gain queue have been selected.
When the end of the channel list is detected, the sequence returns to the first element in the list.

This sequence repeats until the specified number of samples is gathered. You must carefully match the gain to
the expected voltage range on the associated channel — otherwise, an over range condition can occur. Although
this condition does not damage the USB-1208FS, it does produce a useless full-scale reading. It can also
introduce a long recovery time from saturation, which can affect the next measurement in the queue.

Synchronizing multiple units

You can run up to two USB-1208FS units on most computers.

You can connect the SYNC pin of two USB-1208FS units together in a master/slave configuration and acquire
data from the analog inputs of both devices using one clock. When the SYNC pin is configured as an output, the
internal A/D pacer clock is sent to the screw terminal. You can use this signal as a clock input to a second USB
by connecting it to the SYNC pin of the second USB.

When used as a clock input, the SYNC pin operates in one of two modes – Continuous or Gated.

In the default Continuous mode, a USB-1208FS ignores the first clock pulse in order to ensure adequate setup
time. Use this mode if the unit is being paced from a continuous clock source, such as a generator.

In the Gated mode, it is assumed that the clock signal will be held off for an adequate amount of time for setup
to occur. No clock pulses are ignored. Use this mode if the USB-1208FS is set up as a slave and the source of
the external clock is another USB.

The SYNC pin (pin 19) is set for pacer output by default. To set it to input requires a software command (see
Figure 15 on page 24).

To synchronize a master USB-1208FS with a slave USB-1208FS and acquire data, follow the steps below.

1. Connect the SYNC pin of the master USB-1208FS to the SYNC pin of the slave USB-1208FS.

2. Run InstaCal.

3. From the PC Board List on the InstaCal main form, double-click on the USB-1208FS you want to use as a

slave. The Board Configuration dialog opens.

23

USB-1208FS User's Guide Functional Details

4. Select Gated from the Ext. Clock Type drop-down list.

5. Set the Universal Library EXTCLOCK option with cbAInScan()/AInScan for the slave USB-1208FS to

enable pacing from the master USB device.

This InstaCal option does not affect internally paced acquisition. It only affects scans that use the EXTCLOCK
option.

An example of a master/slave configuration is shown below.

Figure 15. Configuring for synchronous data acquisition

When you are operating one USB-1208FS, do not set the EXTCLOCK option unless you are using an external
clock for A/D pacing.

24

Parameter

Conditions

Specification

A/D converter type

Successive approximation type

Input voltage range for linear operation,
single-ended mode

CHx to GND

±10 volts (V) max

Input common-mode voltage range for linear
operation, differential mode

CHx to GND

-10 V min, +20 V max

Absolute maximum input voltage

CHx to GND

±28 V max

Input impedance

122KOhm

Input current (Note 1)

Vin = +10 V

70 microamperes (µA) typ

Vin = 0 V

-12 µA typ

Vin = -10 V

-94 µA typ

Number of channels

8 single-ended / 4 differential, software
selectable

Input ranges, single-ended mode

±10 V, G=2

Input ranges, differential mode

±20 V, G=1
±10 V, G=2
±5 V, G=4
±4 V, G=5
±2.5 V, G=8
±2.0 V, G=10
±1.25 V, G=16
±1.0 V, G=20
Software selectable

Throughput (Note 2)
Software paced

250 samples per second (S/s) typ,
PC-dependent

Continuous scan

50 kilosamples per second (kS/s)

Channel gain queue

Up to 16 elements

Software configurable channel, range, and
gain.

Resolution (Note 3)
Differential

12 bits, no missing codes

Single-ended

11 bits

CAL accuracy

CAL = 2.5 V

±36.25 mV max

Integral linearity error

±1 least significant bit (LSB) typ

Differential linearity error

±0.5 LSB typ

Repeatability

±1 LSB typ

CAL current
Source

5 milliamperes (mA) max

Sink

20 µA min, 100 µA typ

Trigger source

Software selectable

External digital: TRIG_IN

Pacer source

Software selectable

Internal
External (SYNC), rising edge triggered
Programmed IO

Specifications

Typical for 25°C unless otherwise specified.
Specifications in italic text are guaranteed by design.

Analog input

Table 1. Analog input specifications

Chapter 4

Note 1: Input current is a function of applied voltage on the analog input channels. For a given input

voltage, Vin, the input leakage is approximately equal to (8.181*Vin-12) µA.

25

USB-1208FS User's Guide Specifications

Range

Accuracy (LSB)

±20 V

5.1

±10 V

6.1

±5 V

8.1

±4 V

9.1

±2.5 V

12.1

±2 V

14.1

±1.25 V

20.1

±1 V

24.1

Range

Accuracy (LSB)

±10 V

4.0

Range

% of Reading

Gain Error at full scale (FS)
(millivolts (mV))

Offset (mV)

Accuracy at FS (mV)

±20 V

0.2

40

9.766

49.766

±10 V

0.2

20

9.766

29.766

±5 V

0.2

10

9.766

19.766

±4 V

0.2 8 9.766

17.766

±2.5 V

0.2 5 9.766

14.766

±2 V

0.2 4 9.766

13.766

±1.25 V

0.2

2.5

9.766

12.266

±1 V

0.2 2 9.766

11.766

Range

% of Reading

Gain Error at FS (mV)

Offset (mV)

Accuracy at FS (mV)

±10 V

0.2

20

19.531

39.531

Range

Typical counts

Least significant bit

root mean square

(LSB

rms)

±20 V

2

0.30

±10 V

2

0.30

±5 V

3

0.45

±4 V

3

0.45

±2.5 V

4

0.61

±2 V

5

0.76

±1.25 V

7

1.06

±1 V

8

1.21

Note 2: Maximum throughput scanning to PC memory is machine dependent. The rates specified are for

Windows XP only. Maximum rates on operating systems that predate XP may be less and must
be determined through testing on your machine

Note 3: The AD7870 converter only returns 11-bits (0-2047 codes) in single-ended mode.

Table 2. Accuracy, differential mode

Table 3. Accuracy, single-ended mode

Table 4. Accuracy components, differential mode - All values are (±)

Table 5. Accuracy components, single-ended mode - All values are (±)

Table 6. Noise performance, differential mode

26

USB-1208FS User's Guide Specifications

Range

Typical Counts

LSB

rms

±10 V

2

0.30

Parameter

Conditions

Specification

Resolution

12-bits, 1 in 4096

Output range

0 – 4.096 V, 1 mV per LSB.

Number of channels

2

Throughput (Note 4)

Software paced

250 S/s single channel typical, PC dependent

Single channel, continuous scan

10 kS/s

Dual channel, continuous scan,
simultaneous update

5 kS/s
Power on and reset voltage

Initializes to 000h code

Output drive

Each D/A OUT

15 mA

Slew rate

0.8V/microsecond (µs) typ

Range

Accuracy (LSB)

0-4.096 V

4.0 typ, 45.0 max

Range

% of FSR

Gain Error at FS (mV)

Offset (mV)

(Note 5)

Accuracy at FS
(mV)

0-4.096 V

0.1 typ, 0.9 max

4.0 typ, 36.0 max

1.0 typ, 9.0 max

4.0 typ, 45.0 max

Digital type

CMOS

Number of I/O

16 (Port A0 through A7, Port B0 through B7)

Configuration

2 banks of 8

Pull up/pull-down configuration

All pins pulled up to Vs via 47K resistors (default). Positions available for pull
down to ground. Hardware selectable via zero ohm (Ω) resistors as a factory
option.

Input high voltage

2.0 V min, 5.5 V absolute max

Input low voltage

0.8 V max, –0.5 V absolute min

Output high voltage
(IOH = -2.5 mA)

3.8 V min

Output low voltage
(IOL = 2.5 mA)

0.7 V max
Power on and reset state

Input

Table 7. Noise performance, single-ended mode

Analog output

Table 8. Analog output specifications

Note 4: Maximum throughput scanning to PC memory is machine dependent. The rates specified are for

Windows XP only. Maximum rates on operating systems that predate XP may be less and must
be determined through testing on your machine.

Table 10. Analog output accuracy components, all values are (±)

Note 5: Negative offsets will result in a fixed zero-scale error or ―dead band.‖ At the maximum offset of -

9 mV, any input code of less than 0x009 will not produce a response in the output.

Digital input/output

Table 9. Analog output accuracy, all values are (±)

Table 11. Digital I/O specifications

27

USB-1208FS User's Guide Specifications

Parameter

Conditions

Specification

Trigger source (Note 6)

External Digital

TRIG_IN

Trigger mode

Software selectable

Edge sensitive: user configurable for CMOS compatible
rising or falling edge.

Trigger latency

10 µs max

Trigger pulse width

1 µs min

Input high voltage

4.0 V min, 5.5 V absolute max

Input low voltage

1.0 V max, –0.5 V absolute min

Input leakage current

±1.0 µA

Parameter

Conditions

Specification

Pin name

SYNC

Pin type

Bidirectional

Software selectable direction
Output (default)

Outputs internal A/D pacer clock.

Input

Receives A/D pacer clock from external source.

Input clock rate

50 KHz, maximum

Clock pulse width
Input mode

1 µs min

Output mode

5 µs min

Input leakage current

Input mode

±1.0 µA

Input high voltage

4.0 V min, 5.5 V absolute max

Input low voltage

1.0 V max, –0.5 V absolute min

Output high voltage (Note 7)
IOH = -2.5 mA

3.3 V min

No load

3.8 V min

Output low voltage (Note 7)
IOL = 2.5 mA

1.1 V max

No load

0.6 V max

External trigger

Table 12. Digital trigger specifications

Note 6: TRIG_IN is a Schmitt trigger input protected with a 1.5 kilohm (kΩ) series resistor.

External clock input/output

Table 13. External clock I/O specifications

Note 7: SYNC is a Schmitt trigger input and is over-current protected with a 200 Ω series resistor.

28

USB-1208FS User's Guide Specifications

Pin name (Note 8)

CTR

Counter type

Event counter

Number of channels

1

Input type

TTL, rising edge triggered

Input source

CTR screw terminal

Resolution

32 bits

Schmidt trigger hysteresis

20 mV to 100 mV

Input leakage current

±1 µA

Maximum input frequency

1 MHz

High pulse width

500 ns min

Low pulse width

500 ns min

Input high voltage

4.0 V min, 5.5 V absolute max

Input low voltage

1.0 V max, –0.5 V absolute min

EEPROM

1,024 bytes

EEPROM Configuration

Address Range

Access

Description

0x000-0x07F

Reserved

128 bytes system data

0x080-0x1FF

Read/write

384 bytes cal data

0x200-0x3FF

Read/write

512 bytes user area

Type

High performance 8-bit RISC microcontroller

Program Memory

16,384 words

Data Memory

2,048 bytes

Parameter

Conditions

Specification

Supply current (Note 9)

80 mA

+5V USB power available (Note 10)
Connected to self-powered hub
Connected to externally-powered root port hub

4.5 V min, 5.25 V max
Connected to bus-powered hub

4.1 V min, 5.25 V max

Output current (Note 11)
Connected to self-powered hub
Connected to externally-powered root port hub

420 mA max
Connected to bus-powered hub

20 mA max

Counter

Table 14. Counter specifications

Note 8: CTR is a Schmitt trigger input protected with a 1.5K Ω series resistor.

Non-volatile memory

Microcontroller

Power

Table 15. Non-volatile memory specifications

Table 16. Microcontroller specifications

Table 17. Power specifications

Note 9: This is the total current requirement for the USB-1208FS which includes up to 10 mA for the

status LED.

29

USB-1208FS User's Guide Specifications

Parameter

Conditions

Specification

Device type

USB 2.0 full speed

Device compatibility

USB 1.1, USB 2.0

Operating temperature range

0 to 70 °C

Storage temperature range

-40 to 70 °C

Humidity

0 to 90% non-condensing

Dimensions

79 millimeters (mm) long x 82 mm wide x 25 mm high

USB cable length

3 meters max

User connection length

3 meters max

Connector type

Screw terminal

Wire gauge range

16 AWG to 30 AWG

Note 10: Self-powered hub refers to a USB hub with an external power supply. Self-powered hubs allow a

connected USB device to draw up to 500 mA.

Root port hubs reside in the PC’s USB host controller. The USB port(s) on your PC are root port
hubs. All externally powered root port hubs (desktop PCs) provide up to 500 mA of current for a
USB device. Battery-powered root port hubs provide 100 mA or 500 mA, depending upon the
manufacturer. A laptop PC that is not connected to an external power adapter is an example of a
battery-powered root port hub.

Bus powered hubs receive power from a self-powered or root port hub. In this case the
maximum current available from the USB +5 V is 100 mA. The minimum USB +5 V voltage
level can be as low as 4.1 V.

Note 11: This refers to the total amount of current that can be sourced from the USB +5 V, analog outputs

and digital outputs.

General

Table 18. General specifications

Environmental

Table 19. Environmental specifications

Mechanical

Table 20. Mechanical specifications

Main connector and pin out

Table 21. Main connector specifications

30

USB-1208FS User's Guide Specifications

Pin

Signal Name

Pin

Signal Name

1

CH0 IN HI

21

Port A0

2

CH0 IN LO

22

Port A1

3

AGND

23

Port A2

4

CH1 IN HI

24

Port A3

5

CH1 IN LO

25

Port A4

6

AGND

26

Port A5

7

CH2 IN HI

27

Port A6

8

CH2 IN LO

28

Port A7

9

AGND

29

GND

10

CH3 IN HI

30

PC+5V

11

CH3 IN LO

31

GND

12

AGND

32

Port B0

13

D/A OUT 0

33

Port B1

14

D/A OUT 1

34

Port B2

15

AGND

35

Port B3

16

CAL

36

Port B4

17

GND

37

Port B5

18

TRIG_IN

38

Port B6

19

SYNC

39

Port B7

20

CTR

40

GND

Pin

Signal Name

Pin

Signal Name

1

CH0 IN

21

Port A0

2

CH1 IN

22

Port A1

3

AGND

23

Port A2

4

CH2 IN

24

Port A3

5

CH3 IN

25

Port A4

6

AGND

26

Port A5

7

CH4 IN

27

Port A6

8

CH5 IN

28

Port A7

9

AGND

29

GND

10

CH6 IN

30

PC+5V

11

CH7 IN

31

GND

12

AGND

32

Port B0

13

D/A OUT 0

33

Port B1

14

D/A OUT 1

34

Port B2

15

AGND

35

Port B3

16

CAL

36

Port B4

17

GND

37

Port B5

18

TRIG_IN

38

Port B6

19

SYNC

39

Port B7

20

CTR

40

GND

4-channel differential mode

8-channel single-ended mode

31

Declaration of Conformity

Manufacturer: Measurement Computing Corporation
Address: 10 Commerce Way
Suite 1008
Norton, MA 02766
USA
Category: Electrical equipment for measurement, control and laboratory use.

Measurement Computing Corporation declares under sole responsibility that the product

USB-1208FS

to which this declaration relates is in conformity with the relevant provisions of the following standards or other
documents:

EU EMC Directive 89/336/EEC: Electromagnetic Compatibility, EN 61326 (1997) Amendment 1 (1998)

Emissions: Group 1, Class A
 EN 55011 (1990)/CISPR 11: Radiated and Conducted emissions.
Immunity: EN61326, Annex A

 IEC 1000-4-2 (1995): Electrostatic Discharge immunity, Criteria C.
 IEC 1000-4-3 (1995): Radiated Electromagnetic Field immunity Criteria A.
 IEC 1000-4-4 (1995): Electric Fast Transient Burst immunity Criteria C.
 IEC 1000-4-5 (1995): Surge immunity Criteria A.
 IEC 1000-4-6 (1996): Radio Frequency Common Mode immunity Criteria A.
 IEC 1000-4-8 (1994): Magnetic Field immunity Criteria A.
 IEC 1000-4-11 (1994): Voltage Dip and Interrupt immunity Criteria A.

Declaration of Conformity based on tests conducted by Chomerics Test Services, Woburn, MA 01801, USA in
August, 2004. Test records are outlined in Chomerics Test Report #EMI3948.04.

We hereby declare that the equipment specified conforms to the above Directives and Standards.

Carl Haapaoja, Director of Quality Assurance

Measurement Computing Corporation

10 Commerce Way

Suite 1008

Norton, Massachusetts 02766

[phone]

Fax: [phone]

E-mail: [e-mail]

www.mccdaq.com