EVAL-ADT7490EBZ データシートの表示（PDF） - Analog Devices

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EVAL-ADT7490EBZ

dBCool Remote Thermal Monitor and Fan Controller with PECI Interface

Analog Devices 

ADT7490

1

9

1

9

SCL

SDA

0

START BY

MASTER

1

0

1

1

1

0

FRAME 1

SERIAL BUS ADDRESS BYTE

R/W

D7

ACK. BY

ADT7490

1

SCL (CONTINUED)

D6 D5 D4 D3 D2 D1 D0

FRAME 2

ADDRESS POINTER REGISTER BYTE

ACK. BY

ADT7490

9

SDA (CONTINUED)

D7 D6 D5 D4 D3 D2 D1 D0

FRAME 3

DATA BYTE

ACK. BY STOP BY

ADT7490 MASTER

Figure 19. Writing a Register Address to the Address Pointer Register, then Writing Data to the Selected Register

1

9

1

9

SCL

SDA

0

START BY

MASTER

1

0

1

1

1

0 R/W

D7 D6 D5 D4 D3 D2 D1 D0

FRAME 1

SERIAL BUS ADDRESS BYTE

ACK. BY

ADT7490

FRAME 2

ADDRESS POINTER REGISTER BYTE

ACK. BY STOP BY

ADT7490 MASTER

Figure 20. Writing to the Address Pointer Register Only

1

9

1

9

SCL

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

ADT7490

FRAME 2

DATA BYTE FROM ADT7490

Figure 21. 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 possi-

ble 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

protocols, the ADT7490 also supports the read byte protocol

(see System Management Bus Specifications Rev. 2 for more

information; this document is available from the SMBus

organization).

If several read or write operations must be performed in succes-

sion, 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

ADT7490 are discussed here. The following abbreviations are

used in the diagrams:

• S: Start

• P: Stop

• R: Read

• W: Write

• A: Acknowledge

• A: No acknowledge

The ADT7490 uses the following SMBus write protocols.

Rev. 0 | Page 14 of 76

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