Evaluation Board For 22-Bit
Data Acquisition System
EVAL-AD7716EB
a
FEATURES
INTRODUCTION
The EVAL-AD7716EB demonstrates the AD7716, 4-channel,
22-bit A/D Converter. This high-resolution ADC is ideally
suited for biomedical data acquisition systems such as ECG and
EEG as will as general data acquisition applications. Full data
on the AD7716 is available in the AD7716 data sheet availale
from Analog Devices and should be consulted in conjuction
with this document when using the evaluation board.
Included on the evaluation board with the AD7716 are 4 input
buffers, a voltage reference, a crystal oscillator, output interface
circuitry and a 25-Way D-Type connector. The board comes
complete with a cable for connecting directly to the printer port
of a PC.
Software is provided to allow simple demonstration and
evaluation of the AD7716.
4-Channel Data Acquisition Board
22-Bit Resolution
PC Printer Port Compatible
PC-Compatible Software
FUNCTIONAL BLOCK DIAGRAM
DOUT2 DOUT1 DIN1
P1
ANALOG
INPUTS
EVAL-AD7716EB
+5V GND -5V
P2
INPUT
BUFFERS
OUTPUT INTERFACE
25-WAY
D-TYPE
CONNECTOR
AD7716
CRYSTAL
VOLTAGE
REFERENCE
PROTOTYPE AREA
REV. B
Information furnished by Analog Devices is believed to be accurate and
reliable. However, no responsibility is assumed by Analog Devices for its
use, nor for any infringements of patents or other rights of third parties
which may result from its use. No license is granted by implication or
otherwise under any patent or patent rights of Analog Devices.
One Technology Way, P.O. Box 9106, Norwood. MA 02062-9106, U.S.A.
Tel: 617/329-4700
Fax: 617/326-8703
EVAL-AD7716EB
HARDWARE DESCRIPTION
Links and Switches
The circuit diagram for the EVAL-AD7716EB is shown in
Figure 1. The circuit is powered by +/- 5V supplies which are
connected to VDD and VSS. All analog and digital circuitry on
the board is powered from these supplies.
There are a number of links and switches on the board and their
functions are described below.
LK1:
Normally Not Connected. This link connects
the CASCOUT pin to the CASCIN pin of the
AD7716. When the device is operated in this
fashion, a reset must be applied after every write
to the control register.
LK2:
Normally Connected. This link connects the
inverse of DRDY to the CASCIN pin of the
AD7716. When used in this fashion, only one
reset is needed at the start of operation is
needed. The control register may be written to
without further resets.
LK3:
Normally Not Connected. This link allows
IC8 to be bypassed in applications where the
user wishes to keep a common SDATA line.
LK4:
Normally Not Connected. This link, in
association with LK14, allows IC8 to be
bypassed.
SW2-1:
This switch when positioned as in Figure 2, sets
the MODE pin of the AD7716 to a "high".
This sets up the device for the Slave Mode
Interface, which is the interface mode employed
when connected to the PC. In this mode, the
AD7716 is the slave in the system and the
processor is the master.
SW2-2,3,4:
These three switches,when positioned as in
Figure 2, set the device address pins A0, A1, A2
of the AD7716 to "000", respectively. This
information is contained in the data stream
going back to the processor. In a multi-device
system, it is possible to have eight discrete
addresses for eight AD7716, thus making a 32channel data acquisition system. Please consult
the AD7716 data sheet for further details.
Analog Section
The OP-07 input buffers are low noise, low-bandwidth op-amps
and are ideal for buffering the low-bandwidth signals which the
AD7716 will digitise. They have a specified noise spectral
density of 11nV/Root Hz at 600Hz. This corresponds to an rms
noise of 0.25µV in the band, which is more than adequate for
the AD7716.
The AD780 reference is the recommended reference for these
low-noise applications. It provides the necessary +2.5V
reference for the device. It is chosen for its very low noise in the
programmed passband. The AD780 has a typical noise spectral
density of 100nV/Root Hz at 600 Hz. This corresponds to an
rms noise of 2.5µV in this band, which is more than adequate
for the AD7716.
Digital Section
The AD7716 will accept one digital input to the DIN1 pin and
allow transmission back to the host processor. The DIN1 input
is clearly identified at P1 on the board.
The device also allows the user to program two digital outputs.
These outputs are available on DOUT1 and D OUT2 and the state
of these output is displayed on the two LED’s, D1 and D2.
Note that DOUT1 and DOUT2 are also available on P1.
The EVAL-AD7716EB has an on-board 8Mhz crystal oscillator
to run the device. This is a standard parallel resonance crystal
and has two 15pF capacitors connected for stable operation.
On the digital side of the AD7716, the circuitry is designed to
simplify the printer port interface. The SDATA pin of the
device is separated into two (SDATAIN AND SDATAOUT).
The DRDY output pin is used as the handshake signal for the
printer port.
CASCIN and CASCOUT are made available on J2. These
signals allow multiple AD7716’s to be hooked together simply in
multi-device applications.
1
1
1
2
0
3
4
0
Figure 2. SW2 Default Settings
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REV. B
EVAL-AD7716EB
R2
1kΩ
R1
1kΩ
10 kΩ
Figure 1. EVAL-AD7716EB Circuit Diagram
10 kΩ
10 kΩ
Ω
EVAL-AD7716EB
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REV. B
EVAL-AD7716EB
SOFTWARE DESCRIPTION
BOARD CAPABILITIES
The EVAL-AD7716EB comes complete with PC-compatible
software. This software runs under WINDOWS and is largely
button-driven. It consists of several pop-up screens which are
easily navigated. It allows the user to control and evaluate the
AD7716 over the printer port of the PC.
To use the software, the user must have an IBM-compatible PC
and Windows 3.1 must be installed. Start Windows and using
either the RUN command or the File Manager, start the
program called SETUP.EXE on the distribution disk. This
automatically installs the application and sets up a Windows
Group called "ANALOG DEVICES". The application icon is
found here. To start the application, double click on the icon.
When the program starts, the user is asked to select a printer
port. The correct selection depends on the type of computer
being used (Desktop, Laptop, etc,). LPT1 works for most
machines. LPT2 can be used for machines which have two
printer ports. When using a Compaq laptop, select PRN.
Once the printer port has been selected, the user can move to
the MAIN MENU. Once here, the program allows the following functions:
Program the AD7716 Control Register
Reset the AD7716
Gather Data
Graph the Data
Do Noise Analysis
Do a Noise Histogram
Write to a File
Read from a File
The EVAL-AD7716 allows the digital filter in the AD7716 to be
programmed for three cut-off frequencies. These are 36.5Hz,
73Hz and 146Hz. The device itself is capable of operating at
two other cut-off frequencies: 292Hz and 584Hz. However, at
these higer cut-off frequencies it is not possible to transfer all the
device data (128 bits) in the time available, given the speed of
the printer port interface. That is why the feature is not offered
with this package. If operation at these higher cut-off frequencies is desired, then it is recommended that the user interface
the EVAL-AD7716EB to a microcontroller or a DSP microcomputer over a faster serial port.
Because of the many calculations taking place in the program, a
situation can arise where the program can run out of stack
memory. This stack memory stores the variables that are being
used at that particular time. When this happens, either a
message comes up on the screen ("Out Of Stack Space") or the
program buttons cease to function. To resume normal operation, simply quit by double-clicking on the top left-hand corner
of the window, and restart the application.
Note that this is confined to the AD7716 program and does not
affect any other Windows program.
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REV. B
EVAL-AD7716EB
AD7716 Evaluation Software
User Manual
The basic system requirements for running the software supplied with the AD7716 Evaluation Board are as
follows:
•
•
•
•
Microsoft Windows 3.0 or later, running in standard or enhanced mode.
80286 or higher microprocessor.
CGA, EGA, VGA, 8514 Hercules, or other display compatible with Windows.
At least 2Mb of RAM
The software is distributed on a single 1.44Mbyte diskette. The diskette contains 13 files, 11 of which are
installed onto the users system. The files that may be found on the diskette are as follows.
1.
2.
3.
4.
5.
6.
7.
8.
9.
10.
11.
12.
13.
AD7716.EXE
GRAPH.VBX
GSW.EXE
GSWDLL.DLL
PORT7716.DLL
READ.ME
SETUP.EXE
SETUP.LST
SETUPKIT.DLL
THREED.VBX
VBRUN300.DLL
VER.DL_
SETUP1.EXE
The Evaluation Software is distributed with a setup program called SETUP.EXE. This program simplifies the
installation procedure by copying the files on the distribution disk to the correct directories and making a new
program group (called ANALOG DEVICES) in the PROGRAM MANAGER. The application may be found in
this group. The setup program must be started from either the PROGRAM MANAGER
or the FILE
MANAGER in Windows. To start from the PROGRAM MANAGER simply select the RUN option in the
FILE menu and type A:SETUP.EXE and click on OK. If you are using the FILE MANAGER you can simply
click on SETUP.EXE. The setup program will prompt you to select a directory in which to place the program
files. You can use the default selection or type in your own and click on CONTINUE to proceed with the
installation. When the installation is complete the Evaluation Software can be started by double clicking on the
application icon in the program group called ANALOG DEVICES.
Microsoft is a registered trademark and Windows is a
trademark of Microsoft Corp.
REV. B
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EVAL-AD7716EB
PARALLEL PORT SELECTION
The AD7716 evaluation software allows the user to program and gather samples from the AD7716 evaluation
board via the printer port of a PC using the cable supplied. When the program starts up a window called Select A
Parallel Port appears (See Fig.1). The user can select the port they wish to use by clicking on the appropriate
option button and then clicking OK. The hexadecimal numbers displayed beside each option correspond to the
memory address of the port in question. The default selection LPT1 will work in most cases.
Fig. 1 Parallel Port Selection
THE MAIN MENU WINDOW
Once the OK button of the Port Selection window has been pressed the user is presented with the Main Menu
window for the application. The window is called AD7716 Evaluation Software and is shown in Fig. 2 below.
From it the user may :
•
Select the Filter Cutoff Frequency.
•
Program the states of the digital output pins Dout1 and Dout2.
•
Program these selections to the AD7716 Evaluation Board.
•
Read Data from the AD7716 Evaluation Board.
•
Save the data gathered to a file.
•
Load data saved at an earlier date.
•
Graph the data gathered.
•
Do Noise Analysis on the gathered data.
•
Display a Histogram of codes on the data gathered.
•
Quit the program.
Before data can be gathered from the AD7716 Evaluation Board the AD7716 Control Register must be programmed and the device must be reset. If ,on the Evaluation Board, the Cascin is connected to the Cascout via
LK1 then the AD7716 must be reset each time the Control Register is programmed. If the Cascin is connected
to the inverted DRDY via LK2 then resetting the AD7716 is only required once. When this has been done data
can be gathered and examined. Note that changing the "System Options" will not result in a change in the
Control Register of the AD7716 and it is only when the "Program AD7716" button is pressed that these options
are loaded to the AD7716.
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REV. B
EVAL-AD7716EB
Fig. 2 Main Menu
READING DATA FROM THE EVALUATION BOARD
When the "Read Data" button is pressed the READ DATA menu is displayed. This menu allows the user to enter the
number of samples required to be gathered and start the acquisition or return to the main menu. The READ DATA
menu is shown in Fig. 3 below.
Once data has been gathered any of the data analysis functions can be used. Note that these options are not available
until data has either been gathered or a data file has been loaded. A brief description of each of the Data Analysis
functions follows.
Fig.3 Read Data Menu
REV. B
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EVAL-AD7716EB
GRAPHING DATA
The GRAPH DATA window will allow the user to display the acquired data from any one of the four channels
of the AD7716. The required channel is selected by using the option buttons and when the PLOT GRAPH
button is pressed the data from that channel is displayed.
There are three graphs in this window, the top one displays the 22 bit conversion result, the middle one displays
the status of the Overflow bit and the bottom one shows the status of the digital input pin Din1.
The GRAPH DATA window also has the options for the user to return to the Main Menu or to move to either
of the other two data analysis windows.
Note that when the data from the conversion is displayed the MSB is inverted so that the data is displayed in
straight binary rather than 2's complement. This is done to make the graphing routine quicker to execute.
Fig. 4 shows the GRAPH DATA window as it might appear after reading from the AD7716 Evaluation Board.
Fig.4 GRAPH DATA Window
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REV. B
EVAL-AD7716EB
THE NOISE ANALYSIS WINDOW
The NOISE ANALYSIS window, which is shown below in Fig.5, displays information from each of the four
channels of the AD7716. The information displayed includes the standard deviation (in µV ) of the data acquired, the maximum and minimum code acquired (in hexadecimal format), the average code (in hexadecimal
format) and the spread of codes.
The window also has the options of returning to the Main Menu window or to display either the Graph Data or
the Histogram window.
Fig. 5 The NOISE ANALYSIS Window
REV. B
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EVAL-AD7716EB
THE HISTOGRAM WINDOW
The HISTOGRAM window is used to display the number of times each code occurred in a low amplitude
signal. The user can select which channel is to be displayed as a histogram by using the option buttons and then
pressing the "Histogram" button. In order to keep the execution time as short as possible the histogram routine
first checks to see if the span of codes (i.e. the Max code - the Min code) is less than 1500. If the span is greater
than this the program will display an error message and will not perform the histogram operation.
The Histogram window is shown in Fig. 6 below.
Fig. 6 The HISTOGRAM Window
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REV. B
EVAL-AD7716EB
THE SAVE DATA WINDOW
Once data has been acquired from the AD7716 Evaluation Board the user has the option to save the data from
any of the four channels to a file. This is done in the SAVE DATA window shown below in Fig. 7 below. The
data is saved in text format with each code being terminated by a carriage return-line feed. This data can then be
loaded easily into many database or analysis packages for further examination.
Fig. 7 The SAVE DATA Window
REV. B
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EVAL-AD7716EB
THE LOAD DATA WINDOW
The user has the option of loading a file that was saved previously into the AD7716 Evaluation Board software.
The user can select which channel the data is to be loaded into and then by locating the data file using the
window options the file will be loaded and all the analysis functions can be used as normal. The LOAD DATA
window is shown in Fig. 8 below.
Fig. 8 The LOAD DATA Window
NOTE: When using the Load and Save options only the 22 bit conversion result is saved/loaded. The Overflow
and Din1 information is disguarded.
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REV. B