AD9985SLASHPCB datasheet(27/32 Pages) AD

27 / 32 page

AD9985

Rev. 0 | Page 27 of 32

Data is read from the control registers of the AD9985 in a

similar manner. Reading requires two data transfer operations:

The base address must be written with the R/W bit of the slave

address byte low to set up a sequential read operation.

Reading (the R/W bit of the slave address byte high) begins at

the previously established base address. The address of the read

To terminate a read/write sequence to the AD9985, a stop signal

must be sent. A stop signal comprises a low-to-high transition

of SDA while SCL is high.

A repeated start signal occurs when the master device driving

the serial interface generates a start signal without first

generating a stop signal to terminate the current communi-

cation. This is used to change the mode of communication

(read, write) between the slave and master without releasing the

serial interface lines.

Serial Interface Read/Write Examples

Write to one control register

•

Start Signal

•

Slave Address Byte (R/W Bit = Low)

•

Base Address Byte

•

Data Byte to Base Address

•

Stop Signal

Write to four consecutive control registers

•

Start Signal

•

Slave Address Byte (R/W Bit = Low)

•

Base Address Byte

•

Data Byte to Base Address

•

Data Byte to (Base Address + 1)

•

Data Byte to (Base Address + 2)

•

Data Byte to (Base Address + 3)

•

Stop Signal

Read from one control register

•

Start Signal

•

Slave Address Byte (R/W Bit = Low)

•

Base Address Byte

•

Start Signal

•

Slave Address Byte (R/W Bit = High)

•

Data Byte from Base Address

•

Stop Signal

Read from four consecutive control registers

•

Start Signal

•

Slave Address Byte (R/W Bit = Low)

•

Base Address Byte

•

Start Signal

•

Slave Address Byte (R/W Bit = High)

•

Data Byte from Base Address

•

Data Byte from (Base Address + 1)

•

Data Byte from (Base Address + 2)

•

Data Byte from (Base Address + 3)

•

Stop Signal

BIT 7

ACK

BIT 6

BIT 5

BIT 4

BIT 3

BIT 2

BIT 1

BIT 0

SDA

SCL

Figure 13. Serial Interface—Typical Byte Transfer

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