AD7785

Rev. 0 | Page 19 of 32

Table 16. IO Register Bit Designations

Bit Location

Bit Name

Description

IO7 to IO4

0

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

IO3 to IO2

IEXCDIR1 to

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 μA or 210 μA only.

1

1

Both current sources connected to Pin IOUT2. Permitted when the current

sources are set to 10 μA or 210 μA only.

IO1 to IO0

IEXCEN1 to

IEXCEN0

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

excitation currents.

IEXCEN1

IEXCEN0

Current Source Value

0

0

Excitation Current Disabled

0

1

10 μA

1

0

210 μA

1

1

1 mA

OFFSET REGISTER

RS2, RS1, RS0 = 1, 1, 0; Power-On/Reset = 0x800000

Each analog input channel has a dedicated offset register that

holds the offset calibration coefficient for the channel. This

register is 24 bits wide and its power-on/reset value is

0x8000(00). The offset register is used in conjunction 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 AD7785 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 = 0x5XXX00

The full-scale register is a 24-bit register that holds the full-scale

calibration coefficient for the ADC. The AD7785 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 full-scale calibration coef-

ficients, the calibration being performed at gain = 1. Therefore,

every device has different default coefficients. The coefficients

are different depending on whether the internal reference or an

external reference is selected. The default value is automatically

overwritten if an internal or system full-scale calibration is

initiated by the user, or the full-scale register is written to.