ADT7460(2013) データシートの表示（PDF） - ON Semiconductor

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ADT7460
(Rev.:2013)

Remote Thermal Monitor and Fan Controller

ON Semiconductor 

ADT7460

1

9

1

9

SCL

SDA

0

START BY

MASTER

1

0

1

1 A1 A0

FRAME 1

SERIAL BUS ADDRESS BYTE

SCL (CONTINUED)

R/W

D7

ACK. BY

ADT7460

1

D6 D5 D4 D3 D2 D1 D0

FRAME 2

ADDRESS POINTER REGISTER BYTE

9

ACK. BY

ADT7460

SDA (CONTINUED)

D7 D6 D5 D4 D3 D2 D1 D0

FRAME 3

DATA BYTE

ACK. BY STOP BY

ADT7460 MASTER

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

When reading data from a register, there are two

possibilities:

1. If the ADT7460’s 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 ADT7460 as

before, but only the data byte containing the

register address is sent because 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.

2. 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, so Figure 18

can be omitted.

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

without first writing to the address pointer register if the

address pointer register is already at the correct value.

However, it is not possible to write data to a register without

writing to the address pointer register because the first data

byte of a write is always written to the address pointer

register.

In Figure 17 and Figure 19, the serial bus address is shown

as the default value 01011(A1) (A0), where A1 and A0 are

set by the address select mode function previously defined.

In addition to supporting the Send Byte and Receive Byte

protocols, the ADT7460 also supports the Read Byte

protocol (see System Management Bus specifications

Rev. 2.0 for more information).

If it is required to perform several read or write operations

in succession, the master can send a repeat start condition

instead of a stop condition to begin a new operation.

Write Operations

The SMBus specification defines several protocols for

different types of read and write operations. The ones used

in the ADT7460 are discussed below. The following

abbreviations are used in the diagrams:

S − start

P − stop

R − read

W − write

A − acknowledge

A − no acknowledge

The ADT7460 uses the following SMBus write protocols:

Send Byte

In this operation, the master device sends a single

command byte to a slave device as follows:

1. The master device asserts a start condition on SDA.

2. The master sends the 7-bit slave address followed

by the write bit (low).

3. The addressed slave device asserts ACK on SDA.

4. The master sends the register address.

5. The slave asserts ACK on SDA.

6. The master asserts a stop condition on SDA and

the transaction ends.

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