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.

(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

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 k

Ω Resistors

R3

15 k

Ω Resistor

RP1, RP2

100 k

Ω 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