ADT7476A データシートの表示（PDF） - ON Semiconductor

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ADT7476A

Remote Thermal Controller and Voltage Monitor

ON Semiconductor 

ADT7476A

1

91

9

SCL

SDA

0

START BY

MASTER

1 0 1 1 A1 A0

FRAME 1

SERIAL BUS ADDRESS BYTE

R/W

D7

ACK. BY

ADT7476A

D6 D5 D4 D3 D2 D1 D0

NO ACK. BY

FRAME 2

MASTER

DATA BYTE FROM ADT7476A

STOP BY

MASTER

Figure 20. Reading Data from a Previously Selected Register

Write Operations

The SMBus specification defines several protocols for

different types of read and write operations. The ones used

in the ADT7476A 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 ADT7476A 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 ADT7476A, 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.

1

2

3

4

56

S

SLAVE

ADDRESS

W

A

REGISTER

ADDRESS

AP

Figure 21. 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:

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.

1

2

3

4

5 6 78

S

SLAVE

ADDRESS

W

A

REGISTER

ADDRESS

A DATA

AP

Figure 22. Single-byte Write to a Register

Read Operations

The ADT7476A uses the following SMBus read

protocols.

Receive Byte

This operation is useful when repeatedly reading a single

register. The register address is set up beforehand. In this

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 ADT7476A, 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.

1

2

34

S

SLAVE

ADDRESS

R

A

DATA

56

AP

Figure 23. Single-byte Read from a Register

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