AD7731

–20–

REV. 0

READING FROM AND WRITING TO THE ON-CHIP REGISTERS

The AD7731 contains a total of twelve on-chip registers. These registers are all accessed over a three-wire interface. As a result,

addressing of registers is via a write operation to the topmost register on the part, the Communications Register. Figure 5 shows a

flowchart for reading from the different registers on the part summarizing the sequence and the words to be written to access each of

the registers. Figure 6 gives a flowchart for writing to the different registers on the part, again summarizing the sequence and words

to be written to the AD7731.

Byte W

Byte Y

Byte Z

Register

(Hex)

(Hex)

(Hex)

Status Register

10

20

30

Data Register

11

21

30

Mode Register

12

22

30

Filter Register

13

N/A*

N/A*

Offset Register

15

N/A*

N/A*

Gain Register

16

N/A*

N/A*

*N/A = Not Applicable. Continuous reads of these registers does

not make sense as the register contents would remain the same

since they are only changed by a write operation.

Figure 5. Flowchart for Reading from the AD7731 Registers

Register

Byte Y (Hex)

Communications Register

00

Data Register

Read Only Register.

Mode Register

02

Filter Register

03

Offset Register

05

Gain Register

06

Test Register

User is advised not

to change contents of

Test Register

Figure 6. Flowchart for Writing to the AD7731 Registers

START

WRITE

BYTE W TO

COMMUNICATIONS REGISTER

(SEE ACCOMPANYING TABLE)

YES

READ REGISTER

NO

WRITE

BYTE Y TO

COMMUNICATIONS REGISTER

(SEE ACCOMPANYING TABLE)

READ REGISTER

YES

NO

WRITE

BYTE Z TO

COMMUNICATIONS REGISTER

(SEE ACCOMPANYING TABLE)

STOP

CONTINUOUS

READ

OPERATION?

CONTINUOUS

READS OF

REGISTER

REQUIRED?

START

WRITE

BYTE Y TO

COMMUNICATIONS REGISTER

(SEE ACCOMPANYING TABLE)

WRITE TO REGISTER

END