ADT7476ARQZ-R7 datasheet(12/67 Pages) ONSEMI

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ADT7476

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Figure 20. Reading Data from a Previously Selected Register

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 ADT7476A

ACK. BY ADT7476

Write Operations

The SMBus specification defines several protocols for

different types of read and write operations. The ones used

in the ADT7476 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 ADT7476 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 ADT7476, 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 illustrated in

Figure 21.

Figure 21. Setting a Register Address for

Subsequent Read

SLAVE

ADDRESS WA

SA P

ADDRESS

15 6

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:

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.

This operation is illustrated in Figure 22.

Figure 22. Single−Byte Write to a Register

SLAVE

ADDRESS WA

DATA

A P

ADDRESS

7 8

Read Operations

The ADT7476 uses the following SMBus read protocols.

Receive Byte

This operation is useful when repeatedly reading a single

operation, the master device receives a single byte from 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 read bit (high).

3. The addressed slave device asserts ACK on SDA.

4. The master receives a data byte.

5. The master asserts NO ACK on SDA.

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

the transaction ends.

In the ADT7476, the receive byte protocol is used to read

a single byte of data from a register whose address has

previously been set by a send byte or write byte operation.

This operation is illustrated in Figure 23.

Figure 23. Single−Byte Read from a Register

SLAVE

ADDRESS

DATA

SA P

15 6

Alert Response Address

Alert response address (ARA) is a feature of SMBus

devices, allowing an interrupting device to identify itself to

the host when multiple devices exist on the same bus.

The SMBALERT output can be used as either an interrupt

output or an SMBALERT. One or more outputs can be

connected to a common SMBALERT line connected to the

master. If a device’s SMBALERT line goes low, the

following procedure occurs:

1. SMBALERT is pulled low.

ADT7476ARQZ-R7 Datasheet(PDF) 12 Page - ON Semiconductor

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