Measurement Computing us-1208fs User manual

USB-1208FS
Analog and Digital I/O
Document Revision 10A
July 2014
©Copyright 2014
User's Guide

HM USB-1208FS.docx
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into the body, or b) support or sustain life and whose failure to perform can be reasonably expected to result in
injury. Measurement Computing Corporation products are not designed with the components required, and are
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people.

3
Table of Contents
Preface
About this User's Guide .......................................................................................................................5
What you will learn from this user's guide .........................................................................................................5
Conventions in this user's guide .........................................................................................................................5
Where to find more information.........................................................................................................................5
Chapter 1
Introducing the USB-1208FS................................................................................................................6
USB-1208FS block diagram...............................................................................................................................6
Chapter 2
Installing the USB-1208FS....................................................................................................................7
What comes with your shipment?.......................................................................................................................7
Hardware .......................................................................................................................................................................... 7
Software............................................................................................................................................................................ 7
Documentation.................................................................................................................................................................. 7
Unpacking...........................................................................................................................................................7
Installing the software ........................................................................................................................................7
Installing the hardware .......................................................................................................................................7
Chapter 3
Functional Details .................................................................................................................................9
Analog input acquisition modes .........................................................................................................................9
Software paced.................................................................................................................................................................. 9
Hardware paced ................................................................................................................................................................ 9
External components ........................................................................................................................................10
USB connector.................................................................................................................................................................10
LED .................................................................................................................................................................................10
Screw terminals................................................................................................................................................................10
Signal connections............................................................................................................................................11
Analog input....................................................................................................................................................................11
Analog output ..................................................................................................................................................................14
Digital I/O........................................................................................................................................................................14
Counter input...................................................................................................................................................................15
Trigger input....................................................................................................................................................................15
SYNC I/O ........................................................................................................................................................................15
Calibration output............................................................................................................................................................16
Ground.............................................................................................................................................................................16
Power output....................................................................................................................................................................16
Accuracy...........................................................................................................................................................16
Synchronized operations...................................................................................................................................18
Mechanical drawings........................................................................................................................................19
Chapter 4
Specifications......................................................................................................................................20
Analog input.....................................................................................................................................................20
Analog output ...................................................................................................................................................22
Digital I/O.........................................................................................................................................................22
External trigger.................................................................................................................................................23
External clock input/output...............................................................................................................................23
Counter.............................................................................................................................................................24
Non-volatile memory........................................................................................................................................24
Microcontroller.................................................................................................................................................24

USB-1208FS User's Guide
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Power................................................................................................................................................................25
General .............................................................................................................................................................25
Environmental ..................................................................................................................................................25
Mechanical .......................................................................................................................................................25
Screw terminal connector.................................................................................................................................26
Differential mode pinout..................................................................................................................................................26
Single-ended mode pinout ...............................................................................................................................................27
Declaration of Conformity..................................................................................................................28

5
Preface
About this User's Guide
What you will learn from this user's guide
This user's guide describes the Measurement Computing USB-1208FS data acquisition device and lists device
specifications.
Conventions in this user's guide
For more information
Text presented in a box signifies additional information and helpful hints related to the subject matter you are
reading.
Caution! Shaded caution statements present information to help you avoid injuring yourself and others,
damaging your hardware, or losing your data.
bold text Bold text is used for the names of objects on a screen, such as buttons, text boxes, and check boxes.
italic text Italic text is used for the names of manuals and help topic titles, and to emphasize a word or phrase.
Where to find more information
Additional information about the USB-1208FS is available on our website at www.mccdaq.com. You can also
contact Measurement Computing Corporation by phone, fax, or email with specific questions.
Knowledgebase: kb.mccdaq.com
Phone: [phone] and follow the instructions for reaching Tech Support
Fax: [phone] to the attention of Tech Support
Email: [e-mail]

6
Chapter 1
Introducing the USB-1208FS
The USB-1208FS-Plus is an analog input and digital I/O data acquisition device that provides the following
features:
Eight analog input channels that are software-selectable for either eight 11-bit single-ended inputs or four
12-bit differential inputs
Two 12-bit analog output channels
16 digital I/O channels that are independently-selectable as input or output in two 8-bit ports
32-bit event counter input for counting TTL pulses
External digital trigger input
Bidirectional terminal for external clocking or multi-unit synchronization
Screw terminals for field wiring connections
The USB-1208FS is powered by the 5 volt USB supply from your computer. No external power is required.
All I/O connections are made to the device screw terminals.
USB-1208FS block diagram
USB-1208FS functions are illustrated in the block diagram shown here.
Figure 1. USB-1208FS functional block diagram

7
Chapter 2
Installing the USB-1208FS
What comes with your shipment?
The following items are shipped with the USB-1208FS.
Hardware
USB-1208FS
USB cable
Software
MCC DAQ Software CD
Documentation
MCC DAQ Quick Start Guide
The Quick Start Guide booklet provides an overview of the MCC DAQ software you received with the device,
and includes information about installing the software. Please read this booklet completely before installing any
software or hardware.
Unpacking
As with any electronic device, 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 touch either the computer
chassis or other grounded object to eliminate any stored static charge. If the device is damaged, notify
Measurement Computing Corporation immediately by phone, fax, or email.
Knowledgebase: kb.mccdaq.com
Phone: [phone] and follow the instructions for reaching Tech Support
Fax: [phone] to the attention of Tech Support
Email: [e-mail]
For international customers, contact your local distributor. Refer to the International Distributors section on our
web site at www.mccdaq.com/International.
Installing the software
Refer to the Quick Start Guide for instructions on installing the software on the MCC DAQ CD. This booklet is
available in PDF at www.mccdaq.com/PDFmanuals/DAQ-Software-Quick-Start.pdf.
Installing the hardware
Be sure you are using the latest system software
Before installing the device, run Windows Update to update your operating system with the latest HID and USB
drivers.
To connect the USB-1208FS to your system, 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-1208FS installs as a composite device with separate devices attached. When you connect the
USB-1208FS for the first time, a Found New Hardware dialog opens as each device interface is detected. This
is normal. After the device is installed its LED blinks and then remains on. This indicates that communication is
established between the USB-1208FS and your computer.

USB-1208FS User's Guide Installing the USB-1208FS
8
If the LED turns off
If communication is lost between the device and the computer, the LED turns off. To restore communication,
disconnect the USB cable from the computer and then reconnect it. This should restore communication, and the
LED should turn on.

9
Chapter 3
Functional Details
Analog input acquisition modes
The USB-1208FS can acquire analog input data in either software paced or hardware paced mode.
Software paced
The USB-1208FS acquires data one analog sample at a time using software-paced mode. 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.
The maximum sample rate in software paced mode is system-dependent.
Hardware paced
The USB-1208FS can acquire data from up to eight channels using hardware-paced mode. The analog data is
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 A/D converter is paced by either an internal or external clock source.
The maximum sample rate is an aggregate rate. The total sample rate for all channels cannot exceed 50 kS/s.
The following table lists the sample rate when scanning from one to eight channels.
Maximum per channel sample rate
# channels scanned Sample rate (kS/s)
1 50
2 25
3 16.70
4 12.50
5 10
6 8.30
7 7.14
8 6.25
You can start a hardware-paced scan with a software command. Optionally, hardware-paced scans can be
delayed by an external hardware trigger event.

USB-1208FS User's Guide Functional Details
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External components
The external components – screw terminal banks, LED, and USB connector –are shown in Figure 2.
1 Screw terminal pins 21 to 40 3 Screw terminal pins 1 to 20
2 LED 4 USB connector
Figure 2. External components
USB connector
The USB connector provides +5V power and communication. No external power supply is required.
LED
The LED indicates the communication status; it cannot be disabled. LED states are listed in the table below.
LED behavior
LED Illumination Indication
Steady green The USB-1208FS is connected to a computer or external USB hub.
Blinks continuously Data is being transferred.
Screw terminals
The screw terminals provide the following connections:
Eight analog inputs (CH0 IN to CH7 IN)
Two analog outputs (D/A OUT 0 to D/A OUT 1)
16 digital I/O connections (PortA0 to Port A7, and Port B0 to Port B7)
One external trigger input (TRIG_IN)
One external event counter input (CTR)
One SYNC I/O for external clocking and multi-unit synchronization (SYNC)
One calibration output (CAL)
One power output (PC +5 V)
Five analog ground connections (AGND) and four digital ground connections (GND)
One ground connection (GND)
Use 16 AWG to 30 AWG wire when making connections to the screw terminals. The single-ended mode pinout
is shown in Figure 3.

USB-1208FS User's Guide Functional Details
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Figure 3. Single-ended mode pinout
The differential mode pinout is shown in Figure 4.
Figure 4. Differential mode pinout
Signal connections
Analog input
You can connect up to eight single-ended analog input connections to CH0 IN through CH7 IN, or four
differential connections to CH0 IN HI/LO through CH3 IN HI/LO.

USB-1208FS User's Guide Functional Details
12
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 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:
Connect the wire carrying the signal to be measured to CH# IN.
Connect the second wire to AGND.
The input range for single-ended mode is ±10 V.
Single-ended measurements using differential channels
To perform a single-ended measurement using differential channels, connect the signal to the "CH# IN HI"
input, and ground the associated "CH# IN LO" input.
Differential configuration
When 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:
Connect the wire carrying the signal to be measured to CH# IN HI.
Connect the wire carrying the reference signal to CH# IN LO.
Connect the third wire 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 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 5).
Figure 5. 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 [common-
mode 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 6).

USB-1208FS User's Guide Functional Details
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Figure 6. 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 7).
Figure 7. 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.
The table below shows some possible inputs and the expected results.
Sample inputs and differential results
CHHI CHLO Result
–20 V 0 V Invalid
–15 V +5 V Invalid
–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
For more information on analog signal connections
For more information on single-ended and differential inputs, refer to the Guide to DAQ Signal Connections
(this document is available on our web site at www.mccdaq.com/signals)

USB-1208FS User's Guide Functional Details
14
Channel-Gain queue
The channel gain queue feature allows you to set up a scan sequence with a unique per-channel gain setting and
channel sequence. The gain settings are stored in a channel-gain queue list that is written to local memory on
the device.
The channel-gain queue list can contain up to 16 elements in any order. The channel-gain queue list can contain
up to 16 elements in any order. An example of a four-element list is shown in the table below..
Sample channel-gain queue list
Element Channel Range
0 CH0 BIP10V
1 CH0 BIP5V
2 CH7 BIP10V
3 CH2 BIP1V
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 acquired.
Carefully match the gain to the expected voltage range on the associated channel or an over range condition
may occur. Although this condition does not damage the device, it does produce a useless full-scale reading,
and can introduce a long recovery time due to saturation of the input channel.
Analog output
You can connect up to two analog output connections to D/A OUT 0 and D/A OUT 1. 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 5,000 updates per channel. The 0 V to 4.096 V output range provides a convenient 1 mV per
LSB when setting the output voltage levels.
Digital I/O
The device has 16 digital bits that are configured as two 8-bit ports (Port A and Port B). You can connect up to
eight digital I/O lines to each port (terminals Port A0 to Port A7 and Port B0 to Port B7). Each port is
configurable as either input or output.
When configured for input, you can use the digital I/O terminals to detect the state of any TTL level input.
Refer to the schematic shown in Figure 8.
Figure 8. Schematic showing switch detection by digital channel Port A0
If you set the switch to the +5V input, DIO0 reads TRUE (1). When set to GND, Port A0 reads FALSE (0).
For more information on digital signal connections
For more information on digital signal connections and digital I/O techniques, refer to the Guide to DAQ Signal
Connections (available on our web site at www.mccdaq.com/signals).
Pull-up/down configuration
Boards designed with hardware revision D and later have user-configurable internal jumpers to configure the
digital bits for pull-up (default) or pull-down. The hardware revision is listed with the part number on the
bottom of the device, for example P/N 193331D.

USB-1208FS User's Guide Functional Details
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If the p/n of your board is earlier than hardware revision D, the default configuration is pull-up. To configure
for pull-down, the board must be modified at the factory.
If your board has user-configurable jumpers, complete the following steps to set the pull-up/down
configuration:
1. Unplug the device from the computer.
2. Turn the device over and rest the top of the housing on a flat, stable surface.
Caution! The discharge of static electricity can damage some electronic components. Before removing the
USB-1208FS from its housing, ground yourself using a wrist strap or touch the computer chassis
or other grounded object to eliminate any stored static charge.
3. Remove the three screws from the bottom of the device using a #1 Philips head screwdriver.
4. Hold both the top and bottom sections together, turn the device over and rest it on the surface, then
carefully remove the top section of the case to expose the circuit board.
The user-configurable jumpers are labeled DIO A and DIO B. Figure 9 shows the location of the each
jumper on the circuit board.
Figure 9. Pull-up/down jumper locations
5. Configure each jumper for pull-up or pull-down, as shown in Figure 10. Use the jumper labeled DIO A to
configure Port A, and DIO B to configure Port B.
Figure 10. Pull-up/down jumper configuration
6. Replace the top section of the housing, and fasten it to the bottom section with the three screws.
Counter input
The CTR terminal is a 32-bit event counter that can accept frequency inputs up to 1 MHz. The internal counter
increments when the TTL levels transition from low to high.
Trigger input
The TRIG_IN terminal is an external digital trigger input that you can configure for either rising or falling edge.
SYNC I/O
The SYNC terminal is a bidirectional I/O signal that can be configured as an input (default) or an output.
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.

USB-1208FS User's Guide Functional Details
16
Configure as an output to pace conversions on a second USB-1208FS device and acquire data from
16 channels. For more information synchronized operations see page 18.
Calibration output
The CAL terminal is an output used only to calibrate the device. Calibration is software-controlled via InstaCal.
Ground
The analog ground (AGND) terminals provide a common ground for all analog channels. The ground (GND)
connections provide a common ground for the digital, trigger, counter, sync and power terminals.
Power output
The PC +5V terminal is a 5 volt output that is supplied by the computer. You can use this terminal to supply
power to external devices or circuitry.
Caution! The PC +5V 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 USB-
1208FS 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.
Accuracy
The overall accuracy of any instrument is limited by the error components within the system. Resolution is
often used incorrectly to quantify the performance of a measurement product. While "12-bits" or "1 part in
4,096" does indicate what can be resolved, it provides little insight into the quality of an absolute measurement.
Accuracy specifications describe the actual measurement achievable with a USB-1208FS.
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.

USB-1208FS User's Guide Functional Details
17
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 20. We use a ±10 V range
here as an example of what you can expect when performing a measurement in this range.
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.

USB-1208FS User's Guide Functional Details
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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
Synchronized operations
You can run up to two USB-1208FS devices on most computers. You can connect the SYNC pin of two devices
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 signal is sent to the screw
terminal. You can output the clock to the SYNC pin of a second device that is configured for A/D pacer input.

USB-1208FS User's Guide Functional Details
19
Mechanical drawings
Figure 15. Circuit board (top) and enclosure dimensions

20
Chapter 4
Specifications
All specifications are subject to change without notice.
Typical for 25°C unless otherwise specified.
Specifications in italic text are guaranteed by design.
Analog input
Table 1. Analog input specifications
Parameter 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 122 kΩ
Input current (Note 1) Vin = +10 V 70 µA typ
Vin = 0 V –12 µA typ
Vin = –10 V –94 µA typ
Number of channels Software-selectable 8 single-ended / 4 differential
Input ranges, single-ended mode ±10 V, G=2
Input ranges, differential mode
Software-selectable ±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
Throughput (Note 2) Software paced 250 S/s typ, PC-dependent
Hardware paced 50 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 LSB typ
Differential linearity error ±0.5 LSB typ
Repeatability ±1 LSB typ
CAL current Source 5 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
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.
Note 2: Maximum throughput scanning to PC memory is machine dependent.
Note 3: The AD7870 converter only returns 11-bits (0 to 2047 codes) in single-ended mode.