Data Sheet

AD7321

Rev. B | Page 23 of 36

CONTROL REGISTER

The control register is used to select the analog input channel, analog input configuration, reference, coding, and power mode. The

control register is a write only, 12-bit register. Data loaded on the DIN line corresponds to the AD7321 configuration for the next

conversion. Data should be loaded into the control register after the range register has been initialized. The bit functions of the control

register are shown in Table 9 (the power-up status of all bits is 0).

MSB

LSB

15

14

13

12

11

10

9

8

7

6

5

4

3

2

1

0

Write

ZERO

Register Select

ZERO

ZERO

ADD0

Mode 1

Mode 0

PM1

PM0

Coding

Ref

Seq1

Seq2

ZERO

0

Table 9. Control Register Details

Bit

Mnemonic

Description

12, 11, 1

ZERO

A 0 should be written to these bits at all times.

10

ADD0

This channel address bit is used to select the analog input channel for the next conversion if the sequencer

is not being used. If the sequencer is being used, the channel address bit is used to select the final channel

in a consecutive sequence.

9, 8

Mode 1, Mode 0

pins are used in conjunction with the channel address bit. On the AD7321, the analog inputs are

configured as two single-ended inputs, one true differential input pair, or one pseudo differential input

(see Table 10).

7, 6

PM1, PM0

The power management bits are used to select different power mode options on the AD7321 (see Table 11).

5

Coding

This bit is used to select the type of output coding the AD7321 uses for the next conversion result. If

coding = 0, the output coding is twos complement. If coding = 1, the output coding is straight binary.

When operating in sequence mode, the output coding for each channel is the value written to the coding

bit during the last write to the control register.

4

Ref

The reference bit is used to enable or disable the internal reference. If Ref = 0, the external reference is

enabled and used for the next conversion, and the internal reference is disabled. If Ref = 1, the internal

reference is used for the next conversion. When operating in sequence mode, the reference used for each

channel is the value written to the Ref bit during the last write to the control register.

3, 2

Seq1/Seq2

The Sequence 1 and Sequence 2 bits are used to control the operation of the sequencer (see Table 12).

The two analog input channels are configured as one pseudo differential analog input, one true differential input pair, or two single-ended

analog inputs.

Table 10. Analog Input Configuration Selection

Mode 1 = 1, Mode 0 = 1

Mode 1 = 1, Mode 0 = 0

Mode 1 = 0, Mode 0 =1

Mode 1 = 0, Mode 0 = 0

Channel Address Bit

Not Allowed

1 Fully Differential I/P

1 Pseudo Differential I/P

2 Single-Ended I/Ps

ADD0

0

–

–

AGND

1

–

–

AGND