AD7997/AD7998

Rev. 0 | Page 19 of 32

CONFIGURATION REGISTER

The configuration register is a 16-bit read/write register that is used to set the operating mode of the AD7997/AD7998. The 4 MSBs of the

register are unused. The bit functions of all 12 LSBs of the configuration register are outlined in Table 9. A 2-byte write is necessary when

writing to the configuration register.

Table 9. Configuration Register Bits and Default Settings at Power-Up

D15

D14

D13

D12

D11

D10

D9

D8

D7

D6

D5

D4

D3

D2

D1

D0

DONTC

DONTC

DONTC

DONTC

CH8

CH7

CH6

CH5

CH4

CH3

CH2

CH1

FLTR

ALERT

EN

BUSY/

ALERT

ALERT/BUSY

POLARITY

0

0

0

0

0

0

0

0

0

0

0

0

1

0

0

0

Table 10. Bit Function Descriptions

Bit

Mnemonic

Comment

D11 to D4

CH8 to CH1

These 8-channel address bits select the analog input channel(s) to be converted. A 1 in any of Bits D11 to D4

selects a channel for conversion. If more than one channel bit is set to 1, the AD7997/AD7998 sequence

through the selected channels, starting with the lowest channel. All unused channels should be set to 0. Prior

to initiating a conversion, a channel or channels for conversion must be selected in the configuration register.

D3

FLTR

The value written to this bit of the control register determines whether the filtering on SDA and SCL is

enabled or is to be bypassed. If this bit is a 1, then the filtering is enabled; if it is a 0, the filtering is bypassed.

D2

ALERT EN

The hardware ALERT function is enabled if this bit is set to 1, and disabled if this bit is set to 0. This bit is used

in conjunction with the BUSY/ALERT bit to determine if the ALERT/BUSY pin acts as an ALERT or a BUSY

output (see Table 12).

D1

BUSY/ALERT

This bit is used in conjunction with the ALERT EN bit to determine if the ALERT/ BUSY output, Pin 17, acts as

an ALERT or BUSY output (see Table 12), and if Pin 17 is configured as an ALERT output pin, if it is to be reset.

D0

BUSY/ALERT

POLARITY

This bit determines the active polarity of the ALERT/BUSY pin regardless of whether it is configured as an

ALERT or BUSY output. It is active low if this bit is set to 0, and active high if set to 1.

Table 11. Channel Selection

D11

D10

D9

D8

D7

D6

D5

D4

Selected Analog Input Channel

Comments

0

0

0

0

0

0

0

1

0

0

0

0

0

0

1

0

0

0

0

0

0

1

0

0

0

0

0

0

1

0

0

0

0

0

0

1

0

0

0

0

0

0

1

0

0

0

0

0

0

1

0

0

0

0

0

0

1

0

0

0

0

0

0

0

If more than one channel is

selected, the AD7997/AD7998

start converting on the selected

sequence of channels starting with

the lowest channel in the

sequence.

Table 12. ALERT/BUSY Function

D2

D1

ALERT/BUSY Pin Configuration

0

0

Pin does not provide any interrupt signal.

0

1

Pin configured as a BUSY output.

1

0

Pin configured as an ALERT output.

1

1

Resets the ALERT output pin, the Alert_Flag bit in the conversion result register, and the entire alert status register

(if any is active). If 1/1 is written to Bits D2/D1 in the configuration register to reset the ALERT pin, the Alert_Flag bit,

and the alert status register, the contents of the configuration register read 1/0 for D2/D1, respectively, if read back.