AD7490

Data Sheet

Rev. D | Page 12 of 28

INTERNAL REGISTER STRUCTURE

CONTROL REGISTER

The control register on the AD7490 is a 12-bit, write-only

register. Data is loaded from the DIN pin of the AD7490 on the

falling edge of SCLK. The data is transferred on the DIN line at

the same time as the conversion result is read from the part.

The data transferred on the DIN line corresponds to the

AD7490 configuration for the next conversion. This requires

16 serial clocks for every data transfer. Only the information

provided on the first 12 falling clock edges (after the CS falling

edge) is loaded to the control register. MSB denotes the first bit

in the data stream. The bit functions are outlined in Table 5.

Table 5. Control Register

MSB

LSB

11

10

9

8

7

6

5

4

3

2

1

0

WRITE

SEQ

ADD3

ADD2

ADD1

ADD0

PM1

PM0

SHADOW

WEAK/TRI

RANGE

CODING

Table 6. Control Register Bit Functions

Bit

Name

Description

11

WRITE

The value written to this bit of the control register determines whether the following 11 bits are loaded to the

control register or not. If this bit is a 1, the following 11 bits are written to the control register; if it is a 0, the

remaining 11 bits are not loaded to the control register, and it remains unchanged.

10

SEQ

The SEQ bit in the control register is used in conjunction with the SHADOW bit to control the use of the sequencer

function and access the Shadow register (see Table 9).

9 to 6

ADD3 to

ADD0

These four address bits are loaded at the end of the present conversion sequence and select which analog input

channel is to be converted on in the next serial transfer, or they may select the final channel in a consecutive

sequence, as described in Table 9. The selected input channel is decoded as shown in Table 7. The next channel to

conversion result are also output on DOUT prior to the 12 bits of data (see the Serial Interface section).

5, 4

PM1, PM0

Power management bits. These two bits decode the mode of operation of the AD7490, as shown in Table 8.

3

SHADOW

The SHADOW bit in the control register is used in conjunction with the SEQ bit to control the use of the sequencer

function and access the Shadow register (see Table 9).

2

WEAK/TRI

This bit selects the state of the DOUT line at the end of the current serial transfer. If it is set to 1, the DOUT line is

weakly driven to the ADD3 channel address bit of the ensuing conversion. If this bit is set to 0, DOUT returns to

three-state at the end of the serial transfer. See the Control Register section for more details.

1

RANGE

This bit selects the analog input range to be used on the AD7490. If it is set to 0, the analog input range extends

0

CODING

This bit selects the type of output coding used by the AD7490 for the conversion result. If this bit is set to 0, the

output coding for the part is twos complement. If this bit is set to 1, the output coding from the part is straight

binary (for the next conversion).