ADT7475 データシートの表示（PDF） - ON Semiconductor

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ADT7475

dBCOOL® Remote Thermal Monitor and Fan Controller

ON Semiconductor 

ADT7475

the tenth clock pulse, and then high during the tenth clock

pulse to assert a stop condition.

Any number of bytes of data can be transferred over the

serial bus in one operation, but it is not possible to mix read

and write in one operation because the type of operation is

determined at the beginning and cannot subsequently be

changed without starting a new operation.

In the ADT7475, write operations contain either one or

two bytes, and read operations contain one byte. To write

data to one of the device data registers or read data from it,

the address pointer register must be set so that the correct

data register is addressed, and then data can be written to that

register or read from it. The first byte of a write operation

always contains an address that is stored in the address

pointer register. If data is to be written to the device, the write

operation contains a second data byte that is written to the

register selected by the address pointer register.

This write operation is shown in Figure 13. The device

address is sent over the bus, and then R/W is set to 0. This

is followed by two data bytes. The first data byte is the

1

SCL

address of the internal data register to write to, which is

stored in the address pointer register. The second data byte

is the data to write to the internal data register.

When reading data from a register, there are two

possibilities:

• If the ADT7475 address pointer register value is

unknown or not the desired value, it must first be set to

the correct value before data can be read from the

desired data register. This is done by performing a write

to the ADT7475 as before, but only the data byte

containing the register address is sent, because no data

is written to the register see Figure 14.

A read operation is then performed consisting of the

serial bus address; the R/W bit set to 1, followed by the

data byte read from the data register see Figure 15.

• 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 15.

9

1

9

SDA

0

START BY

MASTER

1

0

1

1

1

0

FRAME 1

SERIAL BUS ADDRESS BYTE

R/W

D7

ACK. BY

ADT7475

1

SCL (CONTINUED)

D6 D5 D4 D3 D2 D1 D0

FRAME 2

ADDRESS POINTER REGISTER BYTE

ACK. BY

ADT7475

9

SDA (CONTINUED)

D7 D6 D5 D4 D3 D2 D1 D0

FRAME 3

DATA BYTE

ACK. BY STOP BY

ADT7475 MASTER

Figure 13. Writing a Register Address to the Address Pointer Register, then Writing Data to the Selected Register

1

9

1

9

SCL

SDA

0

START BY

MASTER

1

0

1

1

1

0

FRAME 1

SERIAL BUS ADDRESS BYTE

R/W

D7

ACK. BY

ADT7475

D6 D5 D4 D3 D2 D1 D0

FRAME 2

ADDRESS POINTER REGISTER BYTE

ACK. BY STOP BY

ADT7475 MASTER

Figure 14. Writing to the Address Pointer Register Only

1

9

1

9

SCL

SDA

0

START BY

MASTER

1

0

1

1

1

0 R/W

D7 D6 D5 D4 D3 D2 D1 D0

FRAME 1

SERIAL BUS ADDRESS BYTE

ACK. BY

ADT7475

FRAME 2

DATA BYTE FROM ADT745

NO ACK. BY STOP BY

MASTER MASTER

Figure 15. Reading Data from a Previously Selected Register

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9

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