Preliminary Technical Data

AD7792/AD7793

REV.PrF 6/04 | Page 17

IO7

IO6

IO5

IO4

IO3

IO2

IO1

IO0

0(0)

0(0)

0(0)

0(0)

IEXCDIR1(0)

IEXCDIR0(0)

IEXCEN1(0)

IEXCEN0(0)

Table 12 Filter Register Bit Designations

Bit Location

Bit Name

Description

IO7-IO4

0

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

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 when the

current sources are set to 10 uA or 200 uA only.

1

1

Both Current Sources connected to pin IOUT2. Permitted when the

current sources are set to 10 uA or 200 uA only.

IO1-IO0

IEXCEN1–

IEXCEN0

Direction of Current Sources Select bits.

IEXCEN1

IEXCEN0

Current Source Value

0

0

Excitation Currents Disabled

0

1

10 uA

1

0

200 uA

1

1

1 mA

OFFSET REGISTER (RS2, RS1, RS0 = 1, 1, 0; POWER-ON/RESET = 0x8000(AD7792)/ 0x800000(AD7793))

Each analog input channel has a dedicated offset register that holds the offset calibration coefficient for the channel. This register is 16

bits wide on the AD7792 and 24 bits wide on the AD7793 and, its power-on/reset value is 8000(00) hex. The offset register is used in con-

junction with its associated full-scale register to form a register pair. The power-on-reset value is automatically overwritten if an internal

or system zero-scale calibration is initiated by the user. The offset register is a read/write register. However, the AD7792/AD7793 must be

in idle mode or power down mode when writing to the offset register.

FULL-SCALE REGISTER (RS2, RS1, RS0 = 1, 1, 1; POWER-ON/RESET = 0x5XX5(AD7792)/ 0x5XXXX5(AD7793))

The full-scale registers is a 16-bit register on the AD7792 and a 24-bit register on the AD7793. The full-scale register holds the full-scale

calibration coefficient for the ADC. The AD7792/AD7793 has 3 full-scale registers, each channel having a dedicated full-scale register.

The full-scale registers are read/write registers, However, when writing to the full-scale registers, the ADC must be placed in power

down mode or idle mode. These registers are configured on power-on with factory-calibrated internal full-scale calibration coefficients,

the factory calibration being performed with the gain set to 1 and using the internal reference. Therefore, every device will have different

default coefficients. These default values are used when the device is operated with a gain of 1 and when the internal reference is selected.

For other gains or when the external reference is used at a gain of 1, these default coefficients will be automatically overwritten if an

internal or system full-scale calibration is initiated by the user. A full-scale calibration should be performed when the gain is changed.