Measurement Computing USB-7204 User manual

USB-7204
Analog and Digital I/O
User's Guide
Document Revision 8
March 2013
© Copyright 2013

HM USB-7204.docx
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3
Table of Contents
Preface
About this User's Guide .......................................................................................................................5
Conventions........................................................................................................................................................5
Where to find more information.........................................................................................................................5
Chapter 1
Introducing the USB-7204....................................................................................................................6
USB-7204 block diagram...................................................................................................................................7
Chapter 2
Installing the USB-7204........................................................................................................................8
What comes with your shipment?.......................................................................................................................8
Hardware .......................................................................................................................................................................... 8
Documentation.................................................................................................................................................................. 8
Unpacking the USB-7204...................................................................................................................................8
Installing the software ........................................................................................................................................8
DAQFlex .......................................................................................................................................................................... 8
Universal Library and InstaCal......................................................................................................................................... 9
Installing the hardware .......................................................................................................................................9
Programming and developing applications.........................................................................................................9
Chapter 3
Functional Details ...............................................................................................................................10
Analog input acquisition modes .......................................................................................................................10
Components......................................................................................................................................................10
USB connector.................................................................................................................................................................10
OEM connector................................................................................................................................................................11
Trigger/Sync connector....................................................................................................................................................11
USB connector.................................................................................................................................................................12
LED indicators.................................................................................................................................................................12
Screw terminals................................................................................................................................................................12
Signal connections............................................................................................................................................13
Analog input ....................................................................................................................................................................13
Analog output ..................................................................................................................................................................15
Digital I/O........................................................................................................................................................................15
Trigger input....................................................................................................................................................................15
SYNC I/O ........................................................................................................................................................................15
Counter input...................................................................................................................................................................16
Power output....................................................................................................................................................................16
Ground.............................................................................................................................................................................16
Accuracy...........................................................................................................................................................17
Channel gain queue ..........................................................................................................................................19
Synchronized operations...................................................................................................................................19
Mechanical drawing .........................................................................................................................................20
Chapter 4
Specifications......................................................................................................................................21
Analog input.....................................................................................................................................................21
Analog output...................................................................................................................................................23
Digital input/output...........................................................................................................................................24
External trigger.................................................................................................................................................24
External clock input/output...............................................................................................................................25
Counter.............................................................................................................................................................25

USB-7204 User's Guide
4
Non-volatile memory........................................................................................................................................25
Microcontroller.................................................................................................................................................26
Indicator LEDs .................................................................................................................................................26
Power................................................................................................................................................................26
General .............................................................................................................................................................27
Environmental ..................................................................................................................................................27
Mechanical .......................................................................................................................................................27
Screw terminal connector and pinout ...............................................................................................................27
OEM connector and pinout (P4).......................................................................................................................29
Trigger/Sync connector and pinout (P5)...........................................................................................................29
Declaration of Conformity..................................................................................................................30

5
Preface
About this User's Guide
This document describes the National Instruments USB-7204 data acquisition device and lists device
specifications.
Conventions
For more information
Text presented in a box signifies additional information related to the subject matter.
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 USB-7204 hardware is available on our website at www.mccdaq.com. You can
also contact Measurement Computing Corporation 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-7204
The USB-7204 is a USB 2.0 full-speed device that is supported under the following operating systems:
Microsoft Windows 7/Vista/XP (32-bit or 64-bit)
Microsoft Windows CE
Macintosh (32-bit or 64-bit)
Linux (32-bit or 64-bit)
The USB-7204 is compatible with both USB 1.1 and USB 2.0 ports.
The device that provides the following features:
8 channels of 16-bit analog input
oConfigurable for eight 11-bit single-ended inputs (represented as 12-bit data —even values only) or
four 12-bit differential inputs.
Two 12-bit analog outputs
16 individually configurable digital I/O channels
32-bit event counter
Digital trigger input
Bidirectional SYNC pin for external clocking and synchronization with another board
The device is powered by the +5 volt USB supply from your computer, and requires no external power.

USB-7204 User's Guide Introducing the USB-7204
7
USB-7204 block diagram
USB-7204 functions are illustrated in the block diagram shown here.
Figure 1. USB-7204 functional block diagram

8
Chapter 2
Installing the USB-7204
What comes with your shipment?
The following items are shipped with the USB-7204:
Hardware
USB-7204
USB cable
Optional hardware
OEM connector cable
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.
Insert
The operating systems that are supported by the device are listed on the insert, and includes the internet location
where you can download DAQFlex software, and the locations where you can learn more about DAQFlex
software and MCC DAQ software.
Unpacking the USB-7204
As with any electronic device, you should take care while handling to avoid damage from static
electricity. Before removing the USB-7204 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, contact us immediately using one of the following methods:
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
website at www.mccdaq.com/International.
Installing the software
Note: Before installing the USB-7204 hardware, you must install the software you plan to use with the device.
The USB-7204 is supported by DAQFlex software and Universal Library software. You can install both
software packages on your computer.
DAQFlex
Install DAQFlex software when you want to develop data acquisition applications that can be deployed across
multiple operating systems and custom embedded systems.
DAQFlex software for each supported operating system is available from the DAQFlex download page at
www.mccdaq.com/DAQFlexDL. Refer to the DAQFlex Software User's Guide at
www.mccdaq.com/pdfs/manuals/DAQFlex%20Software.pdf for instructions about how to installing DAQFlex
software.

USB-7204 User's Guide Installing the USB-7204
9
Universal Library and InstaCal
Install Universal Library and InstaCal when you want to develop data acquisition applications using Windows
programming languages.
Universal Library and InstaCal software are included on the CD that ships with the device. Refer to the Quick
Start Guide booklet for instructions about installing Universal Library and InstaCal software.
Installing the hardware
Install the software before you install your device
A driver needed to run the USB-7204 is installed when you install the software. Therefore, you need to install
the software package you plan to use before you install the hardware.
For operation on a Windows operating system, we recommend that you run Windows Update to update your
operating system with the latest USB drivers.
There are two ways to connect the USB-7204 to your system:
Connect a USB cable from the USB connector to either a USB port on the computer or to an external USB
hub connected to the computer. No external power is required.
or
Use a 2.54 mm (0.1 in.) box header to connect with the OEM connector. The connector pinout is shown
below:
Pin
Signal Name
Pin
Signal Name
1
N/C
2
VBUS
3
N/C
4
D–
5
N/C (do not connect anything to this pin)
6
D+
7
N/C (do not connect anything to this pin)
8
GND
9
N/C (do not connect anything to this pin)
10
SHIELD
When you connect the USB-7204 for the first time on a computer running Windows, a Found New Hardware
message opens as the device is detected. The installation is complete when the message closes.
After the USB-7204 is installed, the Power LED remains on to indicate that communication is established
between the USB-7204 and your computer.
Caution! Do not disconnect any device from the USB bus while the computer is communicating with the
USB-7204, or you may lose data and/or your ability to communicate with the USB-7204.
If the Power LED turns off
If the Power LED is on but then turns off, the computer has lost communication with the USB-7204. To restore
communication, disconnect the USB cable from the computer, and then reconnect it. This should restore
communication, and the Power LED should turn on.
Programming and developing applications
You can program and develop applications for the USB-7204 using MCC DAQ software and DAQFlex
software. OEM users can create a custom driver for use with the message-based firmware to interface with the
device.
Refer to the Quick Start Guide for information about the Universal Library and InstaCal.
Refer to the DAQFlex Software User's Guide for information about DAQFlex software.
Refer to the Message-based Firmware Specification for information about the message-based firmware.

10
Chapter 3
Functional Details
Analog input acquisition modes
The USB-7204 can acquire analog input data in software paced and continuous scan modes.
Software paced mode
You can acquire one analog sample at a time in software paced mode. You initiate the A/D conversion by
calling a software command. The analog value is converted to digital data and returned to the computer. You
can repeat this procedure for each channel desired until you have the total number of samples that you want
from each channel. The maximum throughput sample rate in software paced mode is system-dependent.
Continuous scan mode
You can acquire data from up to eight channels simultaneously in continuous scan mode. The analog data is
continuously acquired and converted to digital values until you stop the scan. Data is transferred in blocks of up
to 32 samples from the USB-7204 to the memory buffer on your computer.
The maximum continuous scan rate of 50 kS/s is an aggregate rate. 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.
Components
The USB-7204 components are shown in Figure 2.
Figure 2. USB-7204 external components
USB connector
The USB 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.
This connector operates in parallel with the OEM connector —do not connect to both the USB connector and
the OEM connector.

USB-7204 User's Guide Functional Details
11
OEM connector
The OEM connector operates in parallel with the USB connector —do not connect to both the USB connector
and the OEM connector.
The OEM connector is a 0.1" box header. Pins 2, 4, 6, 8, and 10 provide a USB connection, as listed in the
connector pinout below:
OEM connector pinout
Pin
Signal Name
Pin
Signal Name
1
N/C
2
VBUS
3
N/C
4
D–
5
N/C (do not connect anything to this pin)
6
D+
7
N/C (do not connect anything to this pin)
8
GND
9
N/C (do not connect anything to this pin)
10
SHIELD
Modifications are required in order to use the OEM connector
We recommend that you return the device to the factory for this modification.
Should you have the capabilities to perform the modifications, the following change is required: in order to
create a USB connection via the OEM connector, locations R48 and R49 must be populated. We recommend
that you populate with 0603 size 0 Ω resistors or provide solder bridges to close the gaps.
Trigger/Sync connector
The Trigger/Sync connector provides two signals —SYNC and TRIG_IN. These signals are also available on
the screw terminal (see page 15 for details about these signals).
Trigger/Sync connector pinout
Pin
Signal Name
Pin
Signal Name
1
TRIG_IN
2
GND
3
N/C
4
GND
5
SYNC
6
GND
7
N/C
8
GND
9
N/C
10
N/CD
Use a 0.1" box header when making connections to the Trigger/Sync connector.
The Trigger/Sync connector internally connects its SYNC and TRIG_IN pins to the screw terminal via jumpers
P6 and P7.
Figure 3. Jumper P6 and P7 schematic
Sync jumper (P6)
The Sync jumper internally connects the SYNC pin on the Trigger/Sync connector to the SYNC pin on the
screw terminal. Remove this jumper on boards that will not send/receive the SYNC signal through the
SYNC/TRIG connector. Refer to Figure 2 on page 10 for the location of this jumper.

USB-7204 User's Guide Functional Details
12
Trigger jumper (P7)
The Trigger jumper internally connects the TRIG_IN pin on the Trigger/Sync connector to the TRIG_IN pin on
the screw terminal. Remove this jumper on boards that will not send/receive the TRIG signal through the
SYNC/TRIG connector. Refer to Refer to Figure 2 on page 10 for the location of this jumper.
USB connector
The USB 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.
This connector operates in parallel with the OEM connector —do not connect to both the USB connector and
the OEM connector.
LED indicators
The USB-7204 has LEDs for power and communication status. See Figure 2 for the location of each LED.
LED type
Indication
Power
Steady green: The device's microcontroller is connected to a computer or external USB hub.
Status
Blinking green: data is being transferred over the USB bus.
Screw terminals
The screw terminals 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 external event counter connection (CTR)
Five analog ground connections (AGND)
One ground connection (GND)
16 digital I/O connections (Port 0 Bit 0 to Port 0 Bit 7, and Port 1 Bit 0 to Port 1 Bit 7)
One output power connection (+5VUSER)
Three ground connections (GND)
Screw terminal connections are shown in Figure 4.
Figure 4. Screw terminal pinout

USB-7204 User's Guide Functional Details
13
Signal connections
Analog input
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 Figure 4 on page 12 for the location of the analog input pins.
You can configure the analog input channels as eight single-ended channels or four differential channels. By
default, differential mode is configured at power-up.
Single-ended configuration
When configured for single-ended mode, each analog input has 11-bit resolution, due to restrictions imposed by
the A/D converter. With single-ended mode, the input signal is referenced to signal ground 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.
Single-ended measurements using differential channels
To perform a SE measurement using differential channels, connect the signal to the "CH# IN HI" input, and
ground the associated "CH# IN LO" input.
Differential configuration
When configured for differential mode, each analog input has 12-bit resolution. In differential mode, the input
signal is measured with respect to the low input and 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 5).

USB-7204 User's Guide Functional Details
14
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).
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.

USB-7204 User's Guide Functional Details
15
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
Analog output
You can connect up to two analog output connections to screw terminal pins 13 and 14 (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 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
The USB-7204 has two eight-bit ports (Port 0 to Bit 0 to Bit 7 and Port 1 to Bit 0 to Bit 7). Each port is
configurable as either input or output.
Pull up/down configuration
The digital pins are configurable via jumpers for pull-up to USB +5 V (HI) or pull-down to ground (LO).
Jumper JP2 configures Port 0, and JP1 configures Port 1. On power up and reset the DIO pins are configured as
input and pulled by JP1/JP2.
Figure 8. Jumper JP0 and JP1 configuration
When configured for input, the digital I/O terminals can be used to detect the state of any TTL level input.
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/signals.pdf).
Trigger input
The digital trigger input (TRIG_IN) lets you start an acquisition when a signal's rising or falling edge is detected.
This pin is internally connected to the TRIG_IN pin on the Trigger/Sync connector (see page 11).
SYNC I/O
The SYNC terminal is a bidirectional I/O signal that can be configured as an input or an output (default):
Configure as an external clock input to externally pace the A/D conversions from an external source or
another USB-7204. The SYNC terminal supports TTL-level input signals of up to 50 kHz.
When used as a clock input, the SYNC pin operates in one of two modes –slave or gated slave.
oIn slave mode, the USB-7204 ignores the first clock pulse in order to ensure adequate setup time. Use
this mode when the USB-7204 is being paced from a continuous clock source, such as a generator.

USB-7204 User's Guide Functional Details
16
oIn gated slave mode, it is assumed that the clock signal is held off for an adequate amount of time for
setup to occur. No clock pulses are ignored. Use this mode when the source of the external clock is
another USB-7204.
Configure as an output to pace the conversions on another USB-7204.
When 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-7204 by connecting it to the SYNC pin and Trig/SYNC connector
of the second device.
The SYNC pin is internally connected to the SYNC pin on the Trigger/Sync connector (see page 11).
Counter input
The CTR connection is a TTL-level input to a 32-bit event counter. Refer to Figure 4 on page 12 for the location
of this pin. The internal counter increments when the TTL level transitions from low to high. The counter can
count frequencies of up to 1 MHz.
Power output
The +5VUSER output connection is a 5 volt output that is supplied by the host computer.
Caution! Do not connect to an external power supply to this terminal or you may damage the USB-7204
and possibly the computer.
The maximum total output current that can be drawn from all USB-7204 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-7204 to your computer draws 80 mA of current from the USB +5 V supply. Once you
start running applications with the USB-7204, 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-7204, is the difference between the total current requirement of the USB (based on the
application) and the allowed current draw of the computer platform (500 mA for desktop computers and self-
powered hubs, or 100 mA for bus-powered hubs and notebook computers). It shall not exceed 375 mA, based
on the Slo-Blo Fuse current rating connected to the +5V terminal.
With all outputs at their maximum output current, you can calculate the total current requirement of the USB-
7204 USB +5 V as follows:
(USB-7204 @ 80 mA) + (16 DIO @ 2.5 mA ea) + (2 AO @ 15 mA ea ) = 150 mA
For an application running on a computer 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 +5Vuser output screw
terminal. 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 mA to 375 mA range (fuse-rated).
Since laptop computers typically allow up to 100 mA, the USB-7204 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.
Ground
The analog ground (AGND) terminals provide a common ground for all analog channels. The digital ground
(GND) terminals provide a common ground for the digital, trigger, counter, and sync channels and the power
terminal.

USB-7204 User's Guide Functional Details
17
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-7204 are offset and gain. Nonlinearity is small in the USB-7204, and is
not significant as an error source with respect to offset and gain.
Figure 9 shows an ideal, error-free, USB-7204 transfer function. The typical calibrated accuracy of the USB-
7204 is range-dependent, as explained in the Specifications chapter on page 21. We use a ±10 V range here as
an example of what you can expect when performing a measurement in this range.
The accuracy plots in Figure 9 are drawn for clarity and are not drawn to scale.
Figure 9. Ideal ADC transfer function
The USB-7204 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 10 shows the USB-7204 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.

USB-7204 User's Guide Functional Details
18
The accuracy plots in Figure 10 are drawn for clarity and are not drawn to scale.
Figure 10. 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 11 shows the USB-7204 transfer function with gain error. Gain error is easily
converted to voltage by multiplying the full-scale (FS) input by the error.
The accuracy plots in Figure 11 are drawn for clarity and are not drawn to scale.
Figure 11. ADC Transfer function with gain error
For example, the USB-7204 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 12, we have a plot of the error band of the USB-7204 for the
±10 V range. This is a graphical version of the typical accuracy specification of the product.

USB-7204 User's Guide Functional Details
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The accuracy plots in Figure 12 are drawn for clarity and are not drawn to scale
Figure 12. Error band plot
Channel gain queue
Use the device's channel gain queue to set up a scan sequence with a unique per-channel gain setting and
channel sequence. The queue is large enough for up to 16 channel configurations limited to either single-ended
or differential mode.
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-7204. 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
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-7204 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-7204, 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.
Synchronized operations
You can connect the SYNC pin of two USB-7204 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 is sent to the screw terminal. You can use this signal as a clock input to a second USB-
7204 by connecting it to the SYNC pin and Trig/SYNC connector of the second device.

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20
Mechanical drawing
Figure 13. Circuit board dimension