AD7713 datasheet(23/29 Pages) AD

23 / 29 page

REV. D

–22–

AD7713

MICROCOMPUTER/MICROPROCESSOR INTERFACING

The AD7713’s flexible serial interface allows easy interface to

most microcomputers and microprocessors. Figure 15 shows a

flowchart diagram for a typical programming sequence for read-

ing data from the AD7713 to a microcomputer, while Figure 16

shows a flowchart diagram for writing data to the AD7713.

Figures 17 and 18 show some typical interface circuits.

The flowchart in Figure 15 is for continuous read operations

from the AD7713 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. Reading 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 register). A

read operation to the control/calibration registers is 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.

CONFIGURE AND

INITIALIZE

C/ P

SERIAL PORT

BRING

RFS LOW

POLL

DRDY

BRING

RFS,TFS

AND HIGH

START

BRING

RFS HIGH

READ SERIAL BUFFER

REVERSE ORDER

OF BITS

DRDY

LOW?

YES

Figure 15. Flowchart for Continuous Read Operation

to the AD7713

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 AD7713 outputs the MSB first.

The flowchart in Figure 16 is for a single 24-bit write operation

to the AD7713 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. Writing 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 AD7713 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.

CONFIGURE AND

INITIALIZE

C/ P

SERIAL PORT

BRING

RFS AND A0 LOW

BRING

RFS,TFS

AND A0 HIGH

START

END

LOAD DATA FROM

ADDRESS TO

ACCUMULATOR

WRITE DATA FROM

ACCUMULATOR TO

SERIAL BUFFER

BRING

TFS AND A0 HIGH

REVERSE ORDER

OF BITS

Figure 16. Flowchart for Single Write Operation to

the AD7713

AD7713 to 8XC51 Interface

Figure 17 shows an interface between the AD7713 and the 8XC51

microcontroller. The AD7713 is configured for its external clock-

ing mode, while the 8XC51 is configured in its Mode 0 serial

interface mode. The

DRDY line from the AD7713 is connected to

the Port P1.2 input of the 8XC51, so the

DRDY line is polled by

the 8XC51. The

DRDY line can be connected to the INT1 input

of the 8XC51 if an interrupt driven system is preferred.

RFS

AD7713

SDATA

SCLK

TFS

P1.0

P3.0

P3.1

P1.1

P1.2

MODE

DRDY

P1.3

SYNC

DVDD

8XC51

Figure 17. AD7713 to 8XC51 Interface

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