AD7787

Rev. 0 | Page 12 of 20

MODE REGISTER (RS1, RS0 = 0, 1; POWER-ON/RESET = 0×02)

The mode register is an 8-bit register from which data can be read or to which data can be written. This register is used to configure the

ADC for unipolar or bipolar mode, to enable or disable the buffer, or to place the device into power-down mode. Table 9 outlines the bit

designations for the mode register. MR0 through MR7 indicate the bit locations, MR denoting the bits are in the mode register. MR7

denotes the first bit of the data stream. The number in the parenthesis indicates the power-on/reset default status of that bit. Any write to

the setup register resets the modulator and filter and sets the RDY bit.

MR7

MR6

MR5

MR4

MR3

MR2

MR1

MR0

MD1 (0)

MD0 (0)

0 (0)

0 (0)

BO (0)

U/B (0)

BUF (1)

0 (0)

Table 9. Mode Register Bit Designations

Bit

Location

Bit

Name

Description

MR7 to

MR6

MD1 to

MD0

Mode Select Bits. These bits select between continuous conversion mode, single conversion mode, and standby

mode. In continuous conversion mode, the ADC continuously performs conversions and places the result in the

data register. RDY goes low when a conversion is complete. The user can read these conversions by placing the

device in continuous read mode whereby the conversions are automatically placed on the DOUT line when SCLK

pulses are applied. Alternatively, the user can instruct the ADC to output the conversion by writing to the

when conversions are not being performed. When single conversion mode is selected, the ADC powers up and

RDY goes low, and the ADC returns to power-down mode. The conversion remains in the data register and RDY

remains active (low) until the data is read or another conversion is performed (see Table 10).

MR5 to

MR4

0

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

MR3

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. The burnout currents can be enabled only when the

buffer is active.

MR2

U/B

Unipolar/Bipolar Bit. Set by user to enable unipolar coding, i.e., zero differential input results in 0x000000 output

and a full-scale differential input results in 0xFFFFFF output. Cleared by the user to enable bipolar coding. Negative

full-scale differential input results in an output code of 0x000000, zero differential input results in an output code of

0x800000, and a positive full-scale differential input will result in an output code of 0xFFFFFF.

MR1

BUF

Configures the AD7787 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 device operates in buffered mode, allowing the

user to place source impedances on the front end without contributing gain errors to the system.

MR0

0

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

Table 10. Operating Modes

MD1

MD0

Mode

0

0

Continuous Conversion Mode (Default)

0

1

Reserved

1

0

Single Conversion Mode

1

1

Power-Down Mode