AD5758 datasheet(49/72 Pages) AD

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Data Sheet

AD5758

Rev. 0 | Page 49 of 72

READING FROM REGISTERS

The AD5758 has four options for readback mode that can be

configured in the TWO_STAGE_READBACK_SELECT register

(see Table 44). These options are as follows:



Two stage readback



Autostatus readback



Shared SYNC autostatus readback



Echo mode

Two Stage Readback Mode

Two stage readback mode consists of a write to the TWO_

STAGE_READBACK_SELECT register to select the register

location to be read back, followed by a NOP command. To

perform a NOP command, write all zeros to Bits[D15:D0] of

the NOP register. During the NOP command, the contents of

the selected register are available on SDO in the format shown

in Table 23. It is also possible to write a new two stage readback

command during the second frame, such that the corresponding

new data is available on SDO in the subsequent frame (see

Figure 88). Bits[D31:D30] (or Bits[D23:D22], if SPI CRC is not

enabled) = 0b10 are used as part of the synchronization during

readback. The contents of the first write instruction to the TWO_

STAGE_READBACK_SELECT register is shown in Table 24.

Table 23. SDO Contents for Read Operation

MSB

LSB

D23 to D22

D21

D20 to 16

D15 to D0

0b10

FAULT pin status

Data

Table 24. Reading from a Register Using Two Stage Readback Mode

MSB

LSB

D23

D22

D21

D20

D19

D18

D17

D16

[D15:D5]

DUT_AD1

DUT_AD0

0x13

Reserved

READBACK_SELECT[4:0]

SYNC

INPUT WORD SPECIFIES

*NOP

SDI

UNDEFINED

SELECTED REGISTER DATA

CLOCKED OUT

SDO

SCLK

24/

SELECTED REGISTER DATA

CLOCKED OUT

24/

2-STAGE READBACK

*ALTERNATIVELY COULD

WRITE ANOTHER

TWO-STAGE READBACK

NOP

Figure 88. Two Stage Readback Example

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