AD5338ARMZ datasheet(18/28 Pages) AD

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AD5337/AD5338/AD5339

Rev. C | Page 18 of 28

READ OPERATION

When reading data back from the AD5337/AD5338/AD5339

DACs, the user begins with an address byte (R/W = 0), after

which the DAC acknowledges that it is prepared to receive data

by pulling SDA low. This address byte is usually followed by the

pointer byte, which is also acknowledged by the DAC. Then, the

master initiates another start condition (repeated start) and the

address is resent with R/W = 1. This is acknowledged by the

DAC indicating that it is prepared to transmit data. Two bytes

of data are then read from the DAC as shown in Figure 34. A

stop condition follows.

Note that in a read sequence, data bytes are the same as those in

the write sequence, except that don’t cares are read back as 0s.

However, if the master sends an ACK and continues clocking

SCL (no stop is sent), the DAC retransmits the same two bytes

of data on SDA. This allows continuous read back of data from

the selected DAC register. Alternatively, the user can send a

start followed by the address with R/W = 1. In this case, the

previously loaded pointer settings are used and read back of

data can begin immediately.

LEAST SIGNIFICANT DATA BYTE

000

SCL

SDA

SCL

SDA

SCL

SDA

START

CONDITION

MASTER

ADDRESS BYTE

R/W

MSB

ACK

AD533x

POINTER BYTE

LSB

ACK

AD533x

ADDRESS BYTE

REPEATED

START

CONDITION

MASTER

R/W

ACK

AD533x

MSB

DATA BYTE

LSB

ACK

MASTER

STOP

CONDITION

MASTER

ACK

MASTER

LSB

MSB

Figure 34. Read Sequence

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