AD7796/AD7797

Rev. A | Page 14 of 24

CONFIGURATION REGISTER

RS2, RS1, RS0 = 0, 1, 0; Power-On/Reset = 0x0710

The configuration register is a 16-bit read/write register. This register is used to configure the ADC for unipolar or bipolar mode, enable

or disable the burnout currents, and select the analog input channel. Table 15 outlines the bit designations for the configuration register.

CON0 through CON15 indicate the bit locations, with CON denoting that the bits are in the configuration register. CON15 denotes the

first bit of the data stream. The number in brackets indicates the power-on/reset default status of that bit.

MSB

LSB

CON15

CON14

CON13

CON12

CON11

CON10

CON9

CON8

CON7

CON6

CON5

CON4

CON3

CON2

CON1

CON0

0(0)

0(0)

BO(0)

U/B(0)

0(0)

1(1)

1(1)

1(1)

0(0)

0(0)

0(0)

1(1)

0(0)

CH2(0)

CH1(0)

CH0(0)

Table 15. Configuration Register Bit Designations

Bit Location

Bit Name

Description

CON15 to CON14

0

These bits must be programmed with a Logic 0 for correct operation.

CON13

BO

Burnout Current Enable Bit. When this bit is set to 1 by the user, the 100 nA current sources in the signal

path are enabled. When BO = 0, the burnout currents are disabled.

CON12

U/B

Unipolar/Bipolar Bit. Set by user to enable unipolar coding, that is, a zero differential input results in

0x0000(00) output, and a full-scale differential input results in 0xFFFF(FF) output. Cleared by the user to

enable bipolar coding. A negative full-scale differential input results in an output code of 0x0000(00), a

zero differential input results in an output code of 0x8000(00), and a positive full-scale differential input

results in an output code of 0xFFFF(FF).

CON11

0

This bit must be programmed with a Logic 0 for correct operation.

CON10 to CON8

1

These bits must be programmed with a Logic 1 for correct operation.

CON7 to CON5

0

These bits must be programmed with a Logic 0 for correct operation.

CON4

1

This bit must be programmed with a Logic 1 for correct operation.

CON3

0

This bit must be programmed with a Logic 0 for correct operation.

CON2 to CON0

CH2 to CH0

Channel Select bits. Written by the user to select the active analog input channel to the ADC.

CH2

CH1

CH0

Channel

0

0

0

AIN(+) − AIN(–)

0

0

1

Reserved

0

1

0

Reserved

0

1

1

AIN(–) − AIN(–)

1

0

0

Reserved

1

0

1

Reserved

1

1

0

Temp Sensor

1

1

1

DATA REGISTER

RS2, RS1, RS0 = 0, 1, 1; Power-On/Reset = 0x0000 (AD7796)/0x000000 (AD7797)

The conversion result from the ADC is stored in this data register. This is a read-only register. On completion of a read operation from

this register, the RDY bit/pin is set.

ID REGISTER

RS2, RS1, RS0 = 1, 0, 0; Power-On/Reset = 0x5A (AD7796)/0x5B (AD7797)

The identification number for the AD7796/AD7797 is stored in the ID register. This is a read-only register.