AD7785

Rev. 0 | Page 18 of 32

Bit Location

Bit Name

Description

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 to

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 automatically enabled.

With the buffer disabled, the voltage on the analog input pins can be from 30 mV below GND to 30 mV above

to 100 mV within the power supply rails.

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

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

Automatically selects gain = 1/6 and 1.17 V

reference

DATA REGISTER

RS2, RS1, RS0 = 0, 1, 1; Power-On/Reset = 0x00000F

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. This is a 24-bit register. The 20-bit conversion is contained in the 20 MSBs. The 4 LSBs are set to 1.

ID REGISTER

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

The identification number for the AD7785 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 IO 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 and select

the value of the excitation currents. Table 16 outlines the bit designations for the IO register. IO0 through IO7 indicate the bit locations;

IO denotes that the bits are in the IO register. IO7 denotes the first bit of the data stream. The number in parentheses indicates the power-

on/reset default status of that bit.

IO7

IO6

IO5

IO4

IO3

IO2

IO1

IO0

0(0)

0(0)

0(0)

0(0)

IEXCDIR1(0)

IEXCDIR0(0)

IEXCEN1(0)

IEXCEN0(0)