AD7794

Preliminary Technical Data

REV.PrE 6/04 | Page 20

Bit

Location

Bit Name

Description

0

1

0

0

AIN5(+) – AIN5(-)

3

0

1

0

1

AIN6(+) – AIN6(-)

3

0

1

1

0

Temp Sensor

Automatically selects the internal

reference and sets the gain to 1

0

1

1

1

VDD Monitor

Automatically selects the internal 1.17 V

reference and sets the gain to 1/6

1

0

0

0

AIN1(-) – AIN1(-)

0

1

0

0

1

Reserved

1

0

1

0

Reserved

1

0

1

1

Reserved

1

1

0

0

Reserved

1

1

0

1

Reserved

1

1

1

0

Reserved

1

1

1

1

Reserved

DATA REGISTER (RS2, RS1, RS0 = 0, 1, 1; POWER-ON/RESET = 0x000000)

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 = 0xXF)

The Identification Number for the AD7794 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.

IO7

IO6

IO5

IO4

IO3

IO2

IO1

IO0

0(0)

IOEN(0)

IO2DAT(0)

IO1DAT(0)

IEXCDIR1(0)

IEXCDIR0(0)

IEXCEN1(0)

IEXCEN0(0)

Table 12 Filter Register Bit Designations

Bit Location

Bit Name

Description

IO7

0

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

IO6

IOEN

Configures the pins AIN6(+)/P2 and AIN6(-)/P2 are analog input pins or digital output pins.

When this bit is set, the pins are configured as digital output pins P1 and P2.

When this bit is cleared, these pins are configured as analog input pins AIN6(+) and AIN6(-).

IO5-IO4

IO2DAT/IO1DAT

P2/P1 Data.

When IOEN is set, the data for the digital output pins P1 and P2 is written to bits IO2DAT and IO1DAT.

IO3-IO2

IEXCDIR1–

IEXCDIR0

Direction of Current Sources Select bits.

IEXCDIR1

IEXCDIR0

Current Source Direction

0

0

Current Source IEXC1 connected to pin IOUT1, Current Source IEXC2

connected to pin IOUT2

0

1

Current Source IEXC1 connected to pin IOUT2, Current Source IEXC2

connected to pin IOUT1

1

0

Both Current Sources connected to pin IOUT1. Permitted only when the

current sources are set to 10 uA or 200 uA

1

1

Both Current Sources connected to pin IOUT2. Permitted only when the

current sources are set to 10 uA or 200 uA

IO3-IO2

IEXCEN1–

These bits are used to enable and disable the current sources along with selecting the value of the