AD5675 datasheet(21/27 Pages) AD

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Data Sheet

AD5675

Rev. C | Page 21 of 27

READ OPERATION

When reading data back from the AD5675, begin with a start

command followed by an address byte (R/W = 0), after which

the DAC acknowledges that it is prepared to receive data by

pulling SDA low. The address byte must be followed by the

command byte, which determines both the read command that

is to follow and the pointer address to read from; the command

byte is also acknowledged by the DAC. The user configures the

channel to read back the contents of one or more DAC input

registers and sets the readback command to active using the

command byte.

Then, the master establishes a repeated start condition, and the

address is resent with R/W = 1. This byte 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 44. A

NACK condition from the master, followed by a stop condition,

completes the read sequence. If more than one DAC is selected,

DAC 0 is read back by default.

MULTIPLE DAC READBACK SEQUENCE

When reading data back from multiple AD5675 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. The address byte must be followed by the command byte,

which is also acknowledged by the DAC. The user selects the

first channel to read back using the command byte.

Following this sequence, the master establishes a repeated start

condition, and the address is resent with R/W = 1. This byte is

acknowledged by the DAC, indicating that it is prepared to

transmit data. The first two bytes of data are then read from

DAC Input Register n (selected using the command byte), MSB

first, as shown in Figure 44. The next two bytes read back are the

contents of DAC Input Register n + 1, and the next bytes read

back are the contents of DAC Input Register n + 2. Data is read

from the DAC input registers in this auto-incremented fashion

until a NACK followed by a stop condition follows. If the

contents of DAC Input Register 7 are read out, the next two

bytes of data read are the contents of DAC Input Register 0.

FRAME 2

COMMAND BYTE

FRAME 1

SLAVE ADDRESS

R/W

DB23

DB22

DB21

DB20

DB19

DB18

DB17

DB16

START BY

MASTER

ACK BY

AD5675

ACK BY

AD5675

SCL

SDA

ACK BY

AD5675

REPEATED START BY

MASTER

ACK BY

MASTER

FRAME 4

MOST SIGNIFICANT

DATA BYTE n

FRAME 3

SLAVE ADDRESS

ACK BY

MASTER

NACK BY

MASTER

STOP BY

MASTER

FRAME 6

MOST SIGNIFICANT

DATA BYTE n + 1

FRAME 5

LEAST SIGNIFICANT

DATA BYTE n

R/W

DB15

DB14

DB13

DB12

DB11

DB10

DB9

DB8

SDA

SCL

(CONTINUED)

SDA

(CONTINUED)

DB7

DB6

DB5

DB4

DB3

DB2

DB1

DB0

DB15

DB14

DB13 DB12

DB11

DB10

DB9

DB8

Figure 44. I2C Read Operation

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