AD7927

Data Sheet

Rev. D | Page 12 of 28

CONTROL REGISTER

The control register on the AD7927 is a 12-bit, write-only register. Data is loaded from the DIN pin of the AD7927 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 AD7927 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 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 Bit Functions

MSB

LSB

WRITE

SEQ

DONTC

ADD2

ADD1

ADD0

PM1

PM0

SHADOW

DONTC

RANGE

CODING

Table 6. Control Register Bit Function Description

Bit

Mnemonic

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. If this bit is a 1, the following 11 bits are written to the control register; if it is a 0, then 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 10).

9

DONTC

Don’t care.

8 to 6

ADD2 to

ADD0

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

is to be converted 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 address bits corresponding

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

5, 4

PM1, PM0

Power Management Bits. These two bits decode the mode of operation of the AD7927 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 10).

2

DONTC

Don’t care.

1

RANGE

This bit selects the analog input range to be used on the AD7927. If it is set to 0, the analog input range extends

0

CODING

This bit selects the type of output coding the AD7927 uses 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).

Table 7. Channel Selection

ADD2

ADD1

ADD0

Analog Input Channel

0

0

0

0

0

1

0

1

0

0

1

1

1

0

0

1

0

1

1

1

0

1

1

1

Table 8. Power Mode Selection

PM1

PM0

Mode

1

1

Normal Operation. In this mode, the AD7927 remains in full power mode, regardless of the status of any of the

logic inputs. This mode allows the fastest possible throughput rate from the AD7927.

1

0

Full Shutdown. In this mode, the AD7927 is in full shutdown mode with all circuitry on the AD7927 powering

down. The AD7927 retains the information in the control register while in full shutdown. The part remains in full

shutdown until these bits are changed.

0

1

Auto Shutdown. In this mode, the AD7927 automatically enters full shutdown mode at the end of each conversion

when the control register is updated. Wake-up time from full shutdown is 1 μs and the user should ensure that 1

μs has elapsed before attempting to perform a valid conversion on the part in this mode.

0

0

Invalid Selection. This configuration is not allowed.