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ADM1034ARQZ-REEL
(Rev.:2012)

Thermal Monitor and Fan Speed (RPM) Controller

ON Semiconductor 

ADM1034

clock pulse to assert a stop condition. In read

mode, the master device overrides the

acknowledge bit by pulling the data line high

during the low period before the 9th clock pulse.

This is known as no acknowledge. The master

takes the data line low during the low period

before the 10th clock pulse, then high during the

10th clock pulse to assert a stop condition.

It is not possible to mix read and write in one operation,

because the type of operation is determined at the beginning

and cannot be changed without starting a new operation.

To write data to one of the device data registers or to read

data from it, the address pointer register (APR) must be set

so that the correct data register is addressed; then data can be

written into that register or read from it. The first byte of a

write operation always contains an address that is stored in

the APR. If data is to be written to the device, then the write

operation contains a second data byte, which is written to the

register selected by the APR.

As illustrated in Figure 17, the device address is sent over

the bus, followed by R/W set to 0. This is followed by two

data bytes. The first data byte is the address of the internal

data register to be written to, which is stored in the APR. The

second data byte is the data to be written to the internal data

register.

When reading data from a register there are two

possibilities.

If the ADM1034’s APR value is unknown or incorrect, it

must be set to the correct value before data can be read from

the desired data register. To do this, perform a write to the

ADM1034 as before, but send only the data byte containing

the register. (See Figure 18.) A read operation is then

performed, using the serial bus address and the R/W bit set

to 1, followed by the data byte read from the data register.

(See Figure 19.)

However, if the APR is already at the desired address, data

can be read from the corresponding data register without

first writing to the APR. In this case, Figure 18 can be

omitted.

In Figure 17 to Figure 19, the serial bus address is

determined by the state of the LOCATION pin on powerup.

1

9

1

9

SCL

SDA

A6

START BY

MASTER

A5 A4 A3 A2 A1 A0

FRAME 1

SERIAL BUS ADDRESS BYTE

SCL (CONTINUED)

R/W

D7

ACK. BY

ADM1034

1

D6 D5 D4 D3 D2 D1 D0

FRAME 2

ADDRESS POINTER REGISTER BYTE

9

ACK. BY

ADM1034

SDA (CONTINUED)

D7 D6 D5 D4 D3 D2 D1 D0

FRAME 3

DATA BYTE

ACK. BY STOP BY

ADM1034 MASTER

Figure 17. Writing a Register Address to the Address Pointer Register, then Writing Data to the Selected Register

1

9

1

9

SCL

SDA

A6

START BY

MASTER

A5 A4 A3 A2 A1 A0

FRAME 1

SERIAL BUS ADDRESS BYTE

R/W

D7

ACK. BY

ADM1034

D6 D5 D4 D3 D2 D1 D0

FRAME 2

ADDRESS POINTER REGISTER BYTE

ACK. BY

ADM1034

STOP BY

MASTER

Figure 18. Writing to the Address Pointer Register Only (Send Byte)

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