ADT7462ACPZ-R7 datasheet(16/81 Pages) ONSEMI

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ADT7462

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• 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 (see Figure 26).

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

protocols, the ADT7462 also supports the read byte protocol

(see System Management Bus Specifications Rev. 2.0 for

more information).

If several read or write operations must be performed in

succession, then the master can send a repeat start condition,

instead of a stop condition, to begin a new operation.

Figure 24. Writing a Register Address to the Address Pointer Register, then Writing Data to the Selected Register

SCL

SDA

START BY

MASTER

ACK. BY

ADT7462

ACK. BY

ADT7462

ACK. BY

ADT7462

STOP BY

MASTER

FRAME 2

ADDRESS POINTER REGISTER BYTE

FRAME 1

SERIAL BUS ADDRESS BYTE

R/W

SCL (CONTINUED)

SDA (CONTINUED)

FRAME 3 DATA BYTE

Figure 25. Writing to the Address Pointer Register Only

Figure 26. Reading Data from a Previously Selected Register

SCL

SDA

START BY

MASTER

ACK. BY

ADT7462

ACK. BY

ADT7462

STOP BY

MASTER

FRAME 2

ADDRESS POINTER REGISTER BYTE

FRAME 1

SERIAL BUS ADDRESS BYTE

R/W

SCL

SDA

START BY

MASTER

ACK. BY

ADT7462

NO ACK.

BY MASTER

STOP BY

MASTER

FRAME 2

DATA BYTE FROM ADT7462

FRAME 1

SERIAL BUS ADDRESS BYTE

R/W

Write Operations

The SMBus specification defines several protocols for

different types of read and write operations. The ones used

in the ADT7462 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 ADT7462 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 an ACK on SDA.

4. The master sends a command code.

5. The slave asserts an ACK on SDA.

6. The master asserts a stop condition on SDA to end

the transaction.

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