Datasheet

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
REV. A