ADT7490ARQZ-R7 datasheet(12/75 Pages) ONSEMI

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ADT7490

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Figure 18. Writing a Register Address to the Address Pointer Register, then Writing Data to the Selected Register

R/W

SCL

SDA

ACK. BY

ADT7490

START BY

MASTER

ACK. BY

ADT7490

ACK. BY

ADT7490

STOP BY

MASTER

SCL (CONTINUED)

SDA (CONTINUED)

FRAME 1

SERIAL BUS ADDRESS BYTE

FRAME 2

ADDRESS POINTER REGISTER BYTE

FRAME 3

DATA BYTE

R/W

SCL

SDA

ACK. BY

ADT7490

STOP BY

MASTER

START BY

MASTER

FRAME 1

SERIAL BUS ADDRESS BYTE

FRAME 2

ADDRESS POINTER REGISTER BYTE

ACK. BY

ADT7490

R/W

SCL

SDA

NO ACK. BY

MASTER

STOP BY

MASTER

START BY

MASTER

FRAME 1

SERIAL BUS ADDRESS BYTE

FRAME 2

DATA BYTE FROM ADT7490

ACK. BY

ADT7490

Figure 19. Writing to the Address Pointer Register Only

Figure 20. Reading Data from a Previously Selected Register

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

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

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 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.

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.

ADT7490ARQZ-R7 Datasheet(PDF) 12 Page - ON Semiconductor

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