AD7840
REV. B
–13–
DATA ACQUISITION BOARD
Figure 25 shows the AD7840 in a data acquisition circuit. The
corresponding printed circuit board (PCB) layout and silkscreen
are shown in Figures 26 to 28. The board layout has three inter-
face ports: one serial and two parallel. One of the parallel ports
is directly compatible with the ADSP-2100 evaluation board
expansion connector.
Some systems will require the addition of a re-construction filter
on the output of the AD7840 to complete the data acquisition
system. There is a component grid provided near the analog
output on the PCB which may be used for such a filter or any
other output conditioning circuitry. To facilitate this option,
there is a shorting plug (labeled LK1 on the PCB) on the analog
output track. If this shorting plug is used, the analog output
connects to the output of the AD7840; otherwise this shorting
plug can be omitted and a wire link used to connect the analog
output to the PCB component grid.
The board also contains a simple sample-and-hold circuit which
can be used on the output of the AD7840 to extend the very
good performance of the AD7840 over a wider frequency range.
A second wire link (labelled LK2 on the PCB) connects V
OUT
(SKT1) to either the output of this sample-and-hold circuit or
directly to the output of the AD7840.
INTERFACE CONNECTIONS
There are two parallel connectors, labeled SKT4 and SKT6,
and one serial connector, labeled SKT5. A shorting plug option
(LK8 in Figure 25) on the AD7840
CS/SERIAL input config-
ures the DAC for the appropriate interface (see Pin Function
Description).
SKT6 is a 96-contact (3-row) Eurocard connector which is di-
rectly compatible with the ADSP-2100 Evaluation Board Proto-
type Expansion Connector. The expansion connector on the
ADSP-2100 has eight decoded chip enable outputs labeled
ECE1 to ECE8. ECE6 is used to drive the AD7840 CS input
on the data acquisition board. To avoid selecting on-board
sockets at the same time, LK6 on the ADSP-2100 board must
be removed. The AD7840 and ADSP-2100 data lines are
aligned for left justified data transfer.
SKT4 is a 26-way (2-row) IDC connector. This connector con-
tains the same signal contacts as SKT6 and in addition contains
decoded R/
W and STRB inputs which are necessary for
TMS32020 interfacing. This decoded
WR can be selected via
LK4. The pinout for this connector is shown in Figure 29.
SKT5 is a nine-way D-type connector which is meant for serial
interfacing only. The evaluation board has the facility to invert
SYNC line via LK7. This is necessary for serial interfacing be-
tween the AD7840 and DSP processors such as the DSP56000.
The SKT5 pinout is shown in Figure 30.
SKT1, SKT2 and SKT3 are three BNC connectors which pro-
vide connections for the analog output, the
LDAC input and an
external reference input. The use of an external reference is op-
tional; the shorting plug (LK3) connects the REF IN pin to ei-
ther this external reference or to the AD7840’s own internal
reference.
Wire links LK5 and LK6 connect the D11 and D10 inputs to
the data lines for parallel operation. In the serial mode, these
links allow the user to select the required format and justifica-
tion for serial data (see Table I).
POWER SUPPLY CONNECTIONS
The PCB requires two analog power supplies and one 5 V digi-
tal supply. Connections to the analog supplies are made directly
to the PCB as shown on the silkscreen in Figure 26. The con-
nections are labelled V+ and V– and the range for both of these
supplies is 12 V to 15 V. Connection to the 5 V digital supply is
made through any of the connectors (SKT4 to SKT6). The
–5 V analog supply required by the AD7840 is generated from
a voltage regulator on the V– power supply input (IC5 in
Figure 25).
SHORTING PLUG OPTIONS
There are eight shorting plug options which must be set before
using the board. These are outlined below:
LK1 Connects the analog output to SKT1. The analog
output may also be connected to a component grid
for signal conditioning.
LK2 Selects either the AD7840 V
OUT
or the sample-and-
hold output.
LK3 Selects either the internal or external reference.
LK4 Selects the decoded R/W and STRB inputs for
TMS32020 interfacing.
LK5 Configures the D11/FORMAT input.
LK6 Configures the D10/JUSTIFY input.
LK7 Selects either the inverted or noninverted
SYNC.
LK8 Selects either parallel or serial interfacing.
COMPONENT LIST
IC1 AD7840 Digital-to-Analog Converter
IC2 AD711 Op Amp
IC3 ADG201HS High Speed Switch
IC4 74HC221 Monostable
IC5 79L05 Voltage Regulator
IC6 74HC02
C1, C3, C5, C7,
C11, C13, C15, C17 10 µF Capacitors
C2, C4, C6, C8,
C12, C14, C16, C18 0.1 µF Capacitors
C9 330 pF Capacitor
C10 68 pF Capacitor
R1, R2 2.2 kΩ Resistors
R3 15 kΩ Resistor
RP1, RP2 100 kΩ Resistor Packs
LK1, LK2, LK3,
LK4, LK5, LK6,
LK7, LK8 Shorting Plugs
SKT1, SKT2, SKT3 BNC Sockets
SKT4 26-Contact (2-Row) IDC Connector
SKT5 9-Contact D-Type Connector
SKT6 96-Contact (3-Row) Eurocard
Connector
