AD7380 datasheet(23/31 Pages) AD

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Data Sheet

AD7381-4

Rev. 0 | Page 23 of 31

READING FROM DEVICE REGISTERS

All the registers in the device can be read over the serial

interface. A register read is performed by issuing a register read

command followed by an additional SPI command that can be

either a valid command or no operation command (NOP). The

format for a read command is shown in Table 16. Bit D15 must

be set to 0 to select a read command. Bits[D14:D12] contain the

ignored.

WRITING TO DEVICE REGISTERS

All the read/write registers in the AD7381-4 can be written to

over the serial interface. The length of a SPI write access is

determined by the CRC write function. An SPI access is 16-bit

if CRC write is disabled and 24-bit when CRC write is enabled.

The format for a write command is shown in Table 16. Bit D15

must be set to 1 to select a write command. Bits[D14:D12] contain

the register address. The subsequent 12 bits, Bits[D11:D0],

contain the data to be written to the selected register.

CRC

The AD7381-4 has CRC checksum modes that can be used to

improve interface robustness by detecting errors in data

transmissions. The CRC feature is independently selectable for

SPI interface reads and writes. For example, enable the CRC

function for SPI writes to prevent unexpected changes to the

device configuration but do not enable it on SPI reads to

maintain a higher throughput rate. The CRC feature is

controlled by programming of the CRC_W bit and CRC_R bit

in the Configuration 1 register.

CRC Read

If enabled, a CRC consisting of an 8-bit word is appended to the

conversion result or register reads. The CRC is calculated on the

conversion result for ADC A, ADC B, ADC C, and ADC D, and

is output on SDOA. A CRC is also calculated and appended to

The CRC read function can be used in 2-wire SPI mode, 1-wire

SPI mode, 4-wire SPI mode, and resolution boost mode.

CRC Write

To enable the CRC write function the CRC_W bit in the

Configuration 1 register must be set to 1. To set the CRC_W bit

to 1 to enable the CRC feature, a valid CRC must be appended

to the request frame.

After the CRC feature is enabled, all register write requests are

ignored unless they are accompanied by a valid CRC command.

A valid CRC is required to both enable and disable the CRC

write feature.

NOP

READ REG 1

READ REG 2

NOP

SDI

INVALID

RESULT S0

REG 1 DATA

REG 2 DATA

RESULT S3

SDOA

INVALID

RESULT S0

RESULT S3

SDOB

SDOC

SDOD

Figure 42. Register Read

NOP

WRITE REG 1

WRITE REG 2

NOP

SDI

INVALID

RESULT S0

RESULT S1

RESULT S2

SDOx

Figure 43. Register Write

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