REV. A

AD7707

–14–

Table IX. Register Selection

RS2

RS1

RS0

Register

Register Size

000Communications Register

8 Bits

001Setup Register

8 Bits

010Clock Register

8 Bits

011Data Register

16 Bits

100Test Register

8 Bits

101No Operation

110Offset Register

24 Bits

111Gain Register

24 Bits

R/W

Read/Write Select. This bit selects whether the next operation is a read or write operation to the selected register.

A “0” indicates a write cycle for the next operation to the appropriate register, while a “1” indicates a read opera-

tion from the appropriate register.

STBY

Standby. Writing a “1” to this bit puts the part into its standby or power-down mode. In this mode, the part con-

sumes only 8

µA of power supply current. The part retains its calibration coefficients and control word information

when in STANDBY. Writing a “0” to this bit places the part in its normal operating mode. The serial interface on

the AD7707 remains operational when the part is in STBY mode.

CH1–CH0

Channel Select. These two bits select a channel for conversion or for access to the calibration coefficients as out-

lined in Table X. Three pairs of calibration registers on the part are used to store the calibration coefficients fol-

lowing a calibration on a channel. They are shown in Tables VII for the AD7707 to indicate which channel

combinations have independent calibration coefficients. With CH1 at Logic 1 and CH0 at a Logic 0, the part looks

at the LOCOM input internally shorted to itself. This can be used as a test method to evaluate the noise perfor-

mance of the part with no external noise sources. In this mode, the LOCOM input should be connected to an

external voltage within the allowable common-mode range for the part.

Table X. Channel Selection for AD7707

CH1

CH0

AIN

Reference

Calibration Register Pair

0

0

AIN1

LOCOM

Register Pair 0

0

1

AIN2

LOCOM

Register Pair 1

1

0

LOCOM

LOCOM

Register Pair 0

1

1

AIN3

HICOM

Register Pair 2