REV. 0

ADM1032

–9–

1. Although 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, 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.

ALERT OUTPUT

The

ALERT output goes low whenever an out-of-limit mea-

surement is detected, or if the remote temperature sensor is

Several

ALERT outputs can be wire-ORed together, so that the

common line will go low if one or more of the

ALERT outputs

goes low.

The

ALERT output can be used as an interrupt signal to a

processor, or it may be used as an

SMBALERT. Slave devices

on the SMBus can normally not signal to the master that they

want to talk, but the

SMBALERT function allows them to do so.

A6

19

1

9

A5

A4

A3

A2

A1

A0

R/

W

D7

D6

D5

D4

D3

D2

D1

D0

SCLK

SDATA

START BY

MASTER

FRAME 1

SERIAL BUS ADDRESS BYTE

FRAME 2

ADDRESS POINTER REGISTER BYTE

STOP BY

MASTER

ACK. BY

ADM1032

ACK. BY

ADM1032

FRAME 3

DATA BYTE

SDATA (CONTINUED)

SCLK (CONTINUED)

ACK. BY

ADM1032

9

1

D7

D6

D5

D4

D3

D2

D1

D0

Figure 3a. Writing a Register Address to the Address Pointer Register, then Writing Data to the Selected Register

SCLK

SDATA

START BY

MASTER

19

1

9

A6

A5

A4

A3

A2

A1

A0

R/

W

D7

D6

D5

D4

D3

D2

D1

D0

FRAME 1

SERIAL BUS ADDRESS BYTE

FRAME 2

ADDRESS POINTER REGISTER BYTE

STOP BY

MASTER

ACK. BY

ADM1032

ACK. BY

ADM1032

Figure 3b. Writing to the Address Pointer Register Only

SCLK

19

1

9

SDATA

A6

A5

A4

A3

A2

A1

A0

R/

W

D7

D6

D5

D4

D3

D2

D1

D0

START BY

MASTER

FRAME 1

SERIAL BUS ADDRESS BYTE

FRAME 2

DATA BYTE FROM ADM1032

STOP BY

MASTER

ACK. BY

ADM1032

ACK. BY

ADM1032

Figure 3c. Reading Data from a Previously Selected Register

2. Don’t forget that some of the ADM1032 registers have differ-

ent addresses for read and write operations. The write address

of a register must be written to the Address Pointer if data is

to be written to that register, but it is not possible to read

data from that address. The read address of a register must

be written to the Address Pointer before data can be read

from that register.

One or more

ALERT outputs can be connected to a common

SMBALERT line connected to the master. When the

SMBALERT line is pulled low by one of the devices, the fol-

lowing procedure occurs as illustrated in Figure 4.

MASTER

RECEIVES

SMBALERT

MASTER SENDS

ARA AND READ

COMMAND

DEVICE SENDS

ITS ADDRESS

NO

ACK

START

ALERT RESPONSE ADDRESS

RD

ACK

DEVICE ADDRESS

STOP

Figure 4. Use of

SMBALERT