ADT7482

Rev. 0 | Page 18 of 24

1

19

1

00

1

1

0

0

R/W

D7

D6

D5

D4

D3

D2

D1

D0

SCL

SD

9

A

START BY

MASTER

ACK. BY

ADT7482

FRAME 1

SERIAL BUS ADDRESS BYTE

FRAME 2

ADDRESS POINTER REGISTER BYTE

FRAME 3

DATA BYTE

SCL (CONTINUED)

SDA (CONTINUED)

ACK. BY

ADT7482

ACK. BY

ADT7482

STOP BY

MASTER

9

1

D7

D6

D5

D4

D3

D2

D1

D0

Figure 17. Writing a Register Address to the Address Pointer Register, then Writing Data to the Selected Register

1

19

1

00

1

1

0

0

R/W

D7

D6

D5

D4

D3

D2

D1

D0

SCL

9

SDA

START BY

MASTER

ACK. BY

ADT7482

FRAME 1

SERIAL BUS ADDRESS BYTE

FRAME 2

ADDRESS POINTER REGISTER BYTE

ACK. BY

ADT7482

STOP BY

MASTER

Figure 18. Writing to the Address Pointer Register Only

SCL

SDA

START BY

MASTER

ACK. BY

ADT7482

FRAME 1

SERIAL BUS ADDRESS BYTE

FRAME 2

DATA BYTE FROM ADT7482

NO ACK.

BY MASTER

STOP BY

MASTER

19

1

9

1

0

0

1

1

0

0

R/W

D7

D6

D5

D4

D3

D2

D1

D0

Figure 19. Reading from a Previously Selected Register

Reading Data from a Register

When reading data from a register there are two possibilities:

•

If the ADT7482 address pointer register value is unknown

or not the desired value, it is first necessary to set it to the

correct value before data can be read from the desired data

register. This is done by performing a write to the

ADT7482 as before, but only the data byte containing the

register read address is sent, as data is not to be written to

the register. This is shown in Figure 18.

A read operation is then performed consisting of the serial

bus address, R/W bit set to 1, followed by the data byte

read from the data register. This is shown in Figure 19.

•

If the address pointer register is known to be already at the

desired address, data can be read from the corresponding

data register without first writing to the address pointer

register and the bus transaction shown in Figure 18 can be

omitted.

When reading data from a register, it is important to note the

following points:

1.

It is possible to read a data byte from a data register

without first writing to the address pointer register.

However, if the address pointer register is already at the

correct value, it is not possible to write data to a register

without writing to the address pointer register. This is

because the first data byte of a write is always written to the

address pointer register.

2.

Remember that some of the ADT7482 registers have

different addresses for read and write operations. The write

address of a register must be written to the address pointer

if data is to be written to that register, but it may not be

possible to read data from that address. The read address of

a register must be written to the address pointer before

data can be read from that register.