AD7745 datasheet(13/28 Pages) AD

13 / 28 page

AD7745/AD7746

Rev. 0| Page 13 of 28

If a repeated start condition is encountered after the address

pointer byte, all peripherals connected to the bus respond

exactly as outlined above for a start condition, that is, a repeated

start condition is treated the same as a start condition. When a

master device issues a stop condition, it relinquishes control of

the bus, allowing another master device to take control of the

bus. Hence, a master wanting to retain control of the bus issues

successive start conditions known as repeated start conditions.

AD7745/AD7746 RESET

To reset the AD7745/AD7746 without having to reset the entire

I2C bus, an explicit reset command is provided. This uses a

particular address pointer word as a command word to reset the

part and upload all default settings. The AD7745/AD7746 do

not respond to the I2C bus commands (do not acknowledge)

during the default values upload for approximately 150 µs

(max 200 µs).

The reset command address word is 0xBF.

GENERAL CALL

When a master issues a slave address consisting of seven 0s with

the eighth bit (R/W bit) set to 0, this is known as the general call

address. The general call address is for addressing every device

connected to the I2C bus. The AD7745/AD7746 acknowledge

this address and read in the following data byte.

If the second byte is 0x06, the AD7745/AD7746 are reset,

completely uploading all default values. The AD7745/AD7746

do not respond to the I2C bus commands (do not acknowledge)

during the default values upload for approximately 150 µs (max

200 µs).

The AD7745/AD7746 do not acknowledge any other general

call commands.

1–7

START ADDR R/W ACK SUBADDRESS ACK

DATA

ACK

STOP

SDATA

SCLOCK

Figure 24. Bus Data Transfer

DATA

A(S)

SLAVE ADDR A(S)

SUB ADDR

A(S)

LSB = 0

LSB = 1

DATA

SLAVE ADDR A(S)

SUB ADDR

A(S) S

SLAVE ADDR

A(S)

DATA

A(M)

DATA

WRITE

SEQUENCE

READ

SEQUENCE

A(S) = NO-ACKNOWLEDGE BY SLAVE

A(M) = NO-ACKNOWLEDGE BY MASTER

A(S) = ACKNOWLEDGE BY SLAVE

A(M) = ACKNOWLEDGE BY MASTER

S = START BIT

P = STOP BIT

A(S)

A(M)

Figure 25. Write and Read Sequences

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