AD7734 datasheet(22/32 Pages) AD

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AD7734

Rev. 0 | Page 22 of 32

DIGITAL INTERFACE DESCRIPTION

Hardware

The AD7734 serial interface can be connected to the host device

via the serial interface in several different ways.

The CS pin can be used to select the AD7734 as one of several

circuits connected to the host serial interface. When CS is high,

the AD7734 ignores the SCLK and DIN signals and the DOUT

pin goes to the high impedance state. When the CS signal is not

used, connect the CS pin to DGND.

The RDY pin can be polled for high-to-low transition or can

drive the host device interrupt input to indicate that the

AD7734 has finished the selected operation and/or new data

from the AD7734 is available. The host system can also wait a

designated time after a given command is written to the device

before reading. Alternatively, the AD7734 status can be polled.

When the RDY pin is not used in the system, it should be left as

an open circuit. (Note that the RDY pin is always an active

digital output, i.e., it never goes into a high impedance state.)

The RESET pin can be used to reset the AD7734. When not

used, connect this pin to DVDD.

The AD7734 interface can be reduced to just two wires

connecting the DIN and DOUT pins to a single bidirectional

data line. The second signal in this 2-wire configuration is the

SCLK signal. The host system should change the data line

direction with reference to the AD7734 timing specification

(see the Bus Relinquish Time in Table 2). The AD7734 cannot

operate in the continuous read mode in 2-wire serial interface

configuration.

All the digital interface inputs are Schmitt-Triggered; therefore,

the AD7734 interface features higher noise immunity and can

be easily isolated from the host system via optocouplers.

Figure 13, Figure 14, and Figure 15 outline some of the possible

host device interfaces: SPI without using the CS signal

(Figure 13), a DSP interface (Figure 14), and a 2-wire

configuration (Figure 15).

SCLK

DIN

DOUT

RDY

RESET

DGND

DVDD DVDD

AD7734

SCK

MOSI

MISO

INT

68HC11

Figure 13. AD7734 to Host Device Interface, SPI

SCLK

DIN

DOUT

RDY

RESET

DVDD

AD7734

SCLK

INT

TFS

RFS

ADSP-2105

Figure 14. AD7734 to Host Device Interface, DSP

SCLK

DIN

DOUT

RESET

DGND

DVDD

AD7734

P3.1/TXD

P3.0/RXD

8xC51

Figure 15. AD7734 to Host Device Interface, 2-Wire Configuration

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