REV. B

AD7887

–7–

CONTROL REGISTER

The Control Register on the AD7887 is an 8-bit, write-only register. Data is loaded from the DIN pin of the AD7887 on the rising

edge of SCLK. The data is transferred on the DIN line at the same time as the conversion result is read from the part. This requires

16 serial clocks for every data transfer. Only the information provided on the first eight rising clock edges (after CS falling edge) is

loaded to the Control Register. MSB denotes the first bit in the data stream. The bit functions are outlined in Table I. The contents

of the Control Register on power up is all zeros.

Table I. Control Register

MSB

DONTC

ZERO

REF

SIN/DUAL

CH

ZERO

PM1

PM0

Bit

Mnemonic

Comment

7

DONTC

Don’t Care. The value written to this bit of the Control Register is a don’t care, i.e., it doesn’t matter if

the bit is 0 or 1.

6

ZERO

A zero must be written to this bit to ensure correct operation of the AD7887.

5

REF

Reference Bit. With a 0 in this bit, the on-chip reference is enabled. With a 1 in this bit, the on-chip

reference is disabled.

4

SIN/DUAL

Single/Dual Bit. This bit determines whether the AD7887 operates in single-channel or dual-channel

A 1 in this bit selects dual-channel mode and the reference voltage for the ADC is internally connected

obtain best performance from the AD7887, the internal reference should be disabled when operating in

the dual channel mode, i.e., REF = 1.

3

CH

Channel Bit. When the part is selected for dual-channel mode, this bit determines which channel will be

converted for the next conversion. A 0 in this bit selects the AIN0 input while a 1 in this bit selects the

AIN1 input. In single-channel mode, this bit should always be 0.

2

ZERO

A zero must be written to this bit to ensure correct operation of the AD7887.

1, 0

PM1, PM0

Power Management Bits. These two bits decode the mode of operation of the AD7887 as described

below.

Table II. Power Management Options

PM1

PM0

Mode

00

Mode 1

. In this mode, the AD7887 enters shutdown if the CS input is 1 and is in full power mode when

CS is 0. Thus the part comes out of shutdown on the falling edge of CS and enters shutdown on the

rising edge of CS.

01

Mode 2

. In this mode, the AD7887 is always fully powered up, regardless of the status of any of the logic

inputs.

10

Mode 3

. In this mode, the AD7887 automatically enters shutdown mode at the end of each conversion,

regardless of the state of CS.

11

Mode 4

. In this standby mode, portions of the AD7887 are powered down but the on-chip reference

voltage remains powered up. This mode is similar to Mode 3, but allows the part to power up much

faster. The REF bit should be 0 to ensure the on-chip reference is enabled.