ADT7468 datasheet(13/80 Pages) AD

13 / 80 page

ADT7468

Rev. 0 | Page 13 of 80

R/W

SCL

SDA

ACK. BY

ADT7468

STOP BY

MASTER

START BY

MASTER

FRAME 1

SERIAL BUS ADDRESS BYTE

FRAME 2

ADDRESS POINTER REGISTER BYTE

ACK. BY

ADT7468

Figure 17. Writing to the Address Pointer Register Only

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 ADT7468

ACK. BY

ADT7468

Figure 18. 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 register.

In addition to supporting the send byte and receive byte

protocols, the ADT7468 also supports the read byte protocol.

(see System Management Bus Specifications Rev. 2 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 different

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

ADT7468 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 ADT7468 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:

The master device asserts a start condition on SDA.

The master sends the 7-bit slave address followed by the

write bit (low).

The addressed slave device asserts ACK on SDA.

The master sends a command code.

The slave asserts ACK on SDA.

The master asserts a stop condition on SDA and the

transaction ends.

For the ADT7468, the send byte protocol is used to write a

the same address. This operation is illustrated in Figure 19.

SLAVE

ADDRESS

SA P

ADDRESS

Figure 19. Setting a Register Address for Subsequent Read

If the master is required to read data from the register

immediately 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:

The master device asserts a start condition on SDA.

The master sends the 7-bit slave address followed by the

write bit (low).

The addressed slave device asserts ACK on SDA.

The master sends a command code.

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