AD7788/AD7789

Rev. B | Page 13 of 20

MODE REGISTER

(RS1, RS0 = 0, 1; Power-On/Reset = 0x02)

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

range, to set unipolar or bipolar mode, to enable or disable the buffer, or to place the device into power-down mode. Table 11 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 brackets 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.

MSB

LSB

MR7

MR6

MR5

MR4

MR3

MR2

MR1

MR0

MD1[0]

MD0[0]

0[0]

0[0]

0[0]

U/B[0]

1[1]

0[0]

Table 11. 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. DOUT/ 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/ RDY line when SCLK pulses are applied. Alternatively, the user can instruct the ADC to

output the conversion by writing to the communications register. After power-on, the first conversion is

conversion mode, the ADC is placed in power-down mode when conversions are not being performed.

When single conversion mode is selected, the ADC powers up (which takes 1 ms) and performs a single

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

DOUT/ RDY remains active (low) until the data is read or another conversion is performed (see Table 12).

MR5 to MR3

0

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

MR2

U/B

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

000…000 output, and a full-scale differential input results in 111…111 output. Cleared by the user to

enable bipolar coding. Negative full-scale differential input results in an output code of 000…000, zero

differential input results in an output code of 100…000, and a positive full-scale differential input results in

an output code of 111…111.

MR1

1

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

MR0

0

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

Table 12. Operating Modes

MD1

MD0

Mode

0

0

Continuous conversion mode (default)

0

1

Reserved

1

0

Single conversion mode

1

1

Power-down mode

DATA REGISTER

(RS1, RS0 = 1, 1; Power-On/Reset = 0x0000 for the AD7788 and 0x000000 for the AD7789)

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.