AD7792/AD7793

Preliminary Technical Data

REV.PrF 6/04 | Page 16

Bit Location

Bit Name

Description

Written by the user to select the ADC input range as follows

G2

G1

G0

Gain

ADC Input Range (2.5V Reference)

0

0

0

1 (In-Amp not used)

2.5 V

0

0

1

2 (In-Amp not used)

1.25 V

0

1

0

4

625 mV

0

1

1

8

312.5 mV

1

0

0

16

156.2 mV

1

0

1

32

78.125 mV

1

1

0

64

39.06 mV

1

1

1

128

19.53 mV

CON7

REFSEL

Reference Select Bit. The reference source for the ADC is selected using this bit.

REFSEL

Reference Source

0

External Reference applied between REFIN(+) and REFIN(-)

1

Internal Reference Selected

CON6 - CON5

0

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

CON4

BUF

Configures the ADC for buffered or unbuffered mode of operation. If cleared, the ADC operates in

unbuffered mode, lowering the power consumption of the device. If set, the ADC operates in

buffered mode, allowing the user to place source impedances on the front end without

contributing gain errors to the system.

The buffer can be disabled when the gain equals 1 or 2. For higher gains, the buffer is

automaticallyenabled.

CON3

CON2-CON0

0

CH2-CH0

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

Channel Select bits.

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

CH2

CH1

CH0

Channel

Calibration Pair

0

0

0

AIN1(+) – AIN1(-)

0

0

0

1

AIN2(+) – AIN2(-)

1

0

1

0

AIN3(+) – AIN3(-)

2

0

1

1

AIN1(-) – AIN1(-)

0

1

0

0

Reserved

1

0

1

Reserved

1

1

0

Temp Sensor

Automatically Selects Gain = 1 and Internal

Reference

1

1

1

VDD Monitor

Automatically Selects Gain = 1/6 and 1.17 V

Reference

DATA REGISTER (RS2, RS1, RS0 = 0, 1, 1; POWER-ON/RESET = 0x0000(00))

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 = 0xXA (AD7792) / 0xXB (AD7793))

The Identification Number for the AD7792/AD7793 is stored in the ID register. This is a read-only register.

IO REGISTER (RS2, RS1, RS0 = 1, 0, 1; POWER-ON/RESET = 0x00)

The I/O register is an 8-bit register from which data can be read or to which data can be written. This register is used to enable the excitation

currents and select the value of the excitation currents. Table 12 outlines the bit designations for the IO register. IO0 through IO7 indicate

the bit locations, IO denoting the bits are in the IO register. IO7 denotes the first bit of the data stream. The number in brackets indicates the

power-on/reset default status of that bit.