ADATE305 datasheet(37/56 Pages) AD

37 / 56 page

ADATE305

Rev. 0 | Page 37 of 56

READ OPERATION

The read operation is a two-stage operation. First, a word is

shifted in, specifying which register to read. CS is deasserted

for three clock cycles, and then a second word is shifted in to

obtain the readback data. This second word can be either

another operation or an NOP address. If another operation is

shifted in, it needs to shift in at least eight bits of data to read

back the previous specified data. The NOP address can be used

for this read if there is no need to write/read another register. To

maintain the clarity of the operation, it is strongly recommended

that the NOP address be used for all reads.

Any register read that is fewer than 16 bits has zeroes filled in

the top bits to make it a 16-bit word.

READ INSTRUCTION

NOP

XREAD DATA

SCLK

INPUT

SDIN

INPUT

SDOUT

OUTPUT

INPUT

NOTES

1. X = DON’T CARE.

Figure 75. SPI Read Overview

DATA[15:0], VALUE IS A DON’T CARE

CH[1]

R/W

CH[0]

ADDR[4] ADDR[3] ADDR[2] ADDR[1] ADDR[0]

SCLK

INPUT

SDIN

INPUT

SDOUT

OUTPUT

INPUT

NOTES

1. X = DON’T CARE.

Figure 76. SPI Read—Details of Read Request

DATA[15:0], VALUE IS A DON’T CARE

CH[1]

RDATA[15]

RDATA[2]

RDATA[1]

RDATA[0]

RDATA[14]

R/W = 1

ADDR[4:0] = 0x00 (NOP)

CH[0]

SCLK

INPUT

SDIN

INPUT

SDOUT

OUTPUT

INPUT

NOTES

1. RDATA IS THE REGISTER VALUE BEING READ.

2. X = DON’T CARE.

Figure 77. SPI Read—Details of Read Out

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