ANALOG DEVICES EVAL-AD7716EB Service Manual

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Evaluation Board For 22-Bit

a

FEATURES
4-Channel Data Acquisition Board
22-Bit Resolution
PC Printer Port Compatible
PC-Compatible Software

Data Acquisition System

EVAL-AD7716EB

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.

ANALOG

INPUTS

INPUT

BUFFERS

FUNCTIONAL BLOCK DIAGRAM

D

D

2

OUT

OUT

P1

VOLTAGE

REFERENCE

1

1

D

IN

AD7716

+5V GND -5V

P2

OUTPUT INTERFACE

CRYSTAL

EVAL-AD7716EB

CONNECTOR

PROTOTYPE AREA

25-WAY
D-TYPE

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: [phone] Fax: [phone]

EVAL-AD7716EB

HARDWARE DESCRIPTION

The circuit diagram for the EVAL-AD7716EB is shown in
Figure 1. The circuit is powered by +/- 5V supplies which are
connected to V

and VSS. All analog and digital circuitry on

DD

the board is powered from these supplies.

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 D

1 input

IN

is clearly identified at P1 on the board.
The device also allows the user to program two digital outputs.
These outputs are available on D

OUT

1 and D

2 and the state

OUT

of these output is displayed on the two LED’s, D1 and D2.
Note that D

1 and D

OUT

2 are also available on P1.

OUT

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).

DRDY output pin is used as the handshake signal for the

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.

Links and Switches

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.

1

1

2

0

1

3

4

0

Figure 2. SW2 Default Settings

REV. B–2–

EVAL-AD7716EB

10 kΩ

Ω

R2

1kΩ

R1

1kΩ

10 kΩ

10 kΩ

EVAL-AD7716EB

Figure 1. EVAL-AD7716EB Circuit Diagram

REV. B –3–

EVAL-AD7716EB

SOFTWARE DESCRIPTION

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

BOARD CAPABILITIES

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.

REV. B–4–