ADT7475 データシートの表示（PDF） - Analog Devices

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ADT7475

dBCool® Remote Thermal Monitor and Fan Controller

Analog Devices 

ADT7475

1

9

1

9

SCL

SDA

0

START BY

MASTER

1

SCL

1

0

1

1

1

0

FRAME 1

SERIAL BUS ADDRESS BYTE

R/W

D7

ACK. BY

ADT7475

D6 D5 D4 D3 D2 D1 D0

FRAME 2

ADDRESS POINTER REGISTER BYTE

ACK. BY STOP BY

ADT7475 MASTER

Figure 15. Writing to the Address Pointer Register Only

9

1

9

SDA

0

START BY

MASTER

1

0

1

1

1

0 R/W

D7 D6 D5 D4 D3 D2 D1

FRAME 1

SERIAL BUS ADDRESS BYTE

ACK. BY

ADT7475

FRAME 2

DATA BYTE FROM ADT745

Figure 16. Reading Data from a Previously Selected Register

D0

NO ACK. BY STOP BY

MASTER MASTER

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 addition to supporting the send byte and receive byte pro-

tocols, the ADT7475 also supports the read byte protocol.

(See System Management Bus Specifications Rev. 2.0 for more

information; this document is available from Intel.)

If several read or write operations must be performed 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 differ-

ent types of read and write operations. The ones used in the

ADT7475 are discussed in this section. The following

abbreviations are used in the diagrams:

S—START

P—STOP

R—READ

W—WRITE

A—ACKNOWLEDGE

A—NO ACKNOWLEDGE

The ADT7475 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 a command code.

5. The slave asserts ACK on SDA.

6. The master asserts a stop condition on SDA and the

transaction ends.

For the ADT7475, the send byte protocol is used to write a

register address to RAM for a subsequent single byte read from

the same address. This operation is shown in Figure 17.

1

2

3

4

56

S

SLAVE

ADDRESS

W

A

REGISTER

ADDRESS

AP

Figure 17. Setting a Register Address for a Subsequent Read

If the master is required to read data from the register immedi-

ately after setting up the address, it can assert a repeat start

condition immediately after the final ACK and carry out a

single byte read without asserting an intermediate stop

condition.

Write Byte

In this operation, the master device sends a command byte and

one data byte to the 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 a command code.

5. The slave asserts ACK on SDA.

6. The master sends a data byte.

7. The slave asserts ACK on SDA.

8. The master asserts a stop condition on SDA and the

transaction ends.

Rev. A | Page 11 of 68

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