CSB

SDI

SDO

SPI Write n

Register Load

SCLK

Addr n

Data n

Prior Data

Prior Addr

8

1 2

9

24

XFER_REG

0x00FF

Data n

Addr n

8

1 2

9

24

NOP

NOP

0xXXXX

0x00FF

XFER_REG

8

1 2

9

24

CSB

SDI

SDO

SPI Write n

Register Load

SCLK

Addr n

Data n

Prior Data

Prior Addr

8

1 2

9

24

XFER_REG

0x00FF

Data n

Addr n

8

1 2

9

24

DAC161S997

www.ti.com

SNAS621 – JUNE 2013

OPTIONAL PROTECTED SPI WRITES

The DAC161S997 supports an optional SPI protocol intended to provide robust support against SPI write errors.

When PROTECT_REG_WR is set to 1, all register writes require a subsequent XFER_REG command (a write of

0x00FF to XFER_REG[0x01]) to load the transferred data into the register address (see Figure 18). This

requirement provides protection against write errors in an electrically noisy environment.

Figure 18. Protected SPI writes

SPI Write Error Correction

To minimize the chance of a SPI write error, TI recommends to append a NOP command onto the end of every

register write sequence to verify that the XFER_REG is properly executed, as shown in Figure 19.

Figure 19. Protected SPI writes with NOP command

The XFER_REG command combined with the automatic SDO loopback of the previous SPI write data prevents

loading of incorrect data into a register. If the loopback indicates a communication error has occurred (see

Figure 20), the CSB pin is held low and the previous write command is repeated. Although the second SPI

transaction had 48 SCLK pulses instead of 24 pulses, this is not considered a frame error. A frame error is

indicated when the number of SCLK pulses is not an integer multiple of 24.

Copyright © 2013, Texas Instruments Incorporated

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