AD7712 datasheet(24/28 Pages) AD

24 / 28 page

REV. E

–24–

AD7712

YES

BRING

RFS LOW

REVERSE

ORDER OF BITS

BRING

RFS HIGH

POLL

DRDY

CONFIGURE &

INITIALIZE

C/ P

SERIAL PORT

DRDY

LOW?

BRING

RFS, TFS HIGH

READ

SERIAL BUFFER

START

Figure 16. Flowchart for Continuous Read Operations to

the AD7712

The flowchart for Figure 17 is for a single 24-bit write operation

to the AD7712 control or calibration registers. This shows data

being transferred from data memory to the accumulator before

being written to the serial buffer. Some microprocessor systems

will allow data to be written directly to the serial buffer from

data memory. The writing of data to the serial buffer from the

accumulator will generally consist of either two or three write

operations, depending on the size of the serial buffer.

The flowchart also shows the option of the bits being reversed

before being written to the serial buffer. This depends on

whether the first bit transmitted by the microprocessor is the

MSB or the LSB. The AD7712 expects the MSB as the first bit

in the data stream. In cases where the data is being read or

being written in bytes and the data has to be reversed, the bits

will have to be reversed for every byte.

SIMPLIFYING THE EXTERNAL CLOCKING MODE

INTERFACE

In many applications, the user may not require the facility of

writing to the on-chip calibration registers. In this case, the

serial interface to the AD7712 in external clocking mode can be

simplified by connecting the

TFS line to the A0 input of the

AD7712 (see Figure 15). This means that any write to the de-

vice will load data to the control register (since A0 is low while

TFS is low) and any read to the device will access data from the

output data register or from the calibration registers (since A0 is

high while

RFS is low). It should be noted that in this arrange-

ment the user does not have the capability of reading from the

control register.

AD7712

SDATA

SCLK

TFS

FOUR INTER-

FACE LINES

RFS

Figure 15. Simplified Interface with

TFS Connected to A0

Another method of simplifying the interface is to generate the

TFS signal from an inverted RFS signal. However, generating

the signals the opposite way around (

RFS from an inverted

TFS) will cause writing errors.

MICROCOMPUTER/MICROPROCESSOR INTERFACING

The AD7712’s flexible serial interface allows for easy interface

to most microcomputers and microprocessors. Figure 16 shows

a flowchart diagram for a typical programming sequence for

reading data from the AD7712 to a microcomputer while Figure

17 shows a flowchart diagram for writing data to the AD7712.

Figures 18, 19 and 20 show some typical interface circuits.

The flowchart of Figure 16 is for continuous read operations

from the AD7712 output register. In the example shown, the

DRDY line is continuously polled. Depending on the micropro-

cessor configuration, the

DRDY line may come to an interrupt

input in which case the

DRDY will automatically generate an

interrupt without being polled. The reading of the serial buffer

could be anything from one read operation up to three read

operations (where 24 bits of data are read into an 8-bit serial

similar, but in this case the status of

DRDY can be ignored. The

A0 line is brought low when the

RFS line is brought low when

reading from the control register.

The flowchart also shows the bits being reversed after they have

been read in from the serial port. This depends on whether the

microprocessor expects the MSB of the word first or the LSB of

the word first. The AD7712 outputs the MSB first.

AD7712 Datasheet(PDF) 24 Page - Analog Devices

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