AD7298

Preliminary Technical Data

Rev. PrA | Page 8 of 18

CONTROL REGISTER

The control register of the AD7298 is a 16-bit, write-only register. Data is loaded from the DIN pin of the AD7298 on the falling edge of

SCLK. The data is transferred on the DIN line at the same time that the conversion result is read from the part. The data transferred on

the DIN line corresponds to the AD7298 configuration for the next conversion. This requires 16 serial clocks for every data transfer. Only

the information provided on the first 16 falling clock edges (after the falling edge of CS

Table 6. Control Register Bit Functions

) is loaded to the control register. MSB denotes the

first bit in the data stream. The bit functions are outlined in Table 6 and Table 7. On power up the default content of the control register is

all zero’s.

MSB

LSB

D15

D14

D13

D12

D11

D10

D9

D8

D7

D6

D5

D4

D3

D2

D1

D0

WRITE

REPEAT

CH1

CH2

CH3

CH4

CH5

CH6

CH7

CH8

T

SENSE

DONTC

DONTC

EXT_REF

T

PD

Table 7. Control Register Bit Function Description

Bit

Mnemonic

Description

15

WRITE

The value written to this bit of the control register determines whether the following 15 bits are loaded to

the control register. If this bit is a 1, the following 15 bits are written to the control register; if it is a 0, then the

remaining 15 bits are not loaded to the control register and it remains unchanged.

REPEAT

This bit enables the repeated conversion of the selected sequence of channels.

CH1 to CH8

Channel selection bits: These eight bits are loaded at the end of the current conversion and select which analog

input channel is to be converted in the next serial transfer, or they may select the sequence of channels for

Writing a 1 to this bit enables the temperature conversion. When the temperature sensor is selected for conversion

the TSENSE_BUSY pin will go high after the next CS falling edge to indicate that the conversion is in progress, the

previous conversion result can be read while the temperature conversion is in progress. Once TSENSE_Busy goes

DONTC

Don’t care.

EXT_REF

Writing a logic 1 to this bit, enables the use of an external reference. The input voltage range for the external

reference is 2V to 2.5V. The external reference should not exceed 2.5V or the device performance will be affected.

Writing a 1 to this bit enables the temperature sensor averaging function. When averaging is enabled, the AD7298

conversion.

PD

Partial Power Down. This mode is selected by writing a 1 to this bit in the control register. In this mode, some of

the internal analog circuitry is powered down. The AD7298 retains the information in the control register while in

partial power down mode. The part remains in this mode until a 0 is written to this bit.

Table 8. Channel Address bits

ADD3

ADD2

ADD1

ADD0

Analog Input Channel

0

0

0

0

0

0

0

1

0

0

1

0

0

0

1

1

0

1

0

0

0

1

0

1

0

1

1

0

0

1

1

1

1

0

0

0

1

0

0

1

enabled