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ADT7483A
(Rev.:2012)

Dual Channel Temperature Sensor and Over Temperature Alarm

ON Semiconductor 

ADT7483A

1

91

9

SCLK

SDATA

1

START BY

MASTER

0 01101

FRAME 1

SERIAL BUS ADDRESS BYTE

R/W

D7

ACK. BY

ADT7483A

D6 D5 D4 D3 D2 D1 D0

ACK. BY

FRAME 2

ADT7483A

ADDRESS POINTER REGISTER BYTE

STOP BY

MASTER

Figure 16. Writing to the Address Pointer Register Only

1

91

9

SCLK

SDATA

1

START BY

MASTER

0011 01

FRAME 1

SERIAL BUS ADDRESS BYTE

R/W

D7

ACK. BY

ADT7483A

D6 D5 D4 D3 D2 D1 D0

ACK. BY

FRAME 2

MASTER

DATA BYTE FROM ADT7483A

STOP BY

MASTER

Figure 17. Reading Data from a Previously Selected Register

When reading data from a register there are two

possibilities:

1. If the address pointer register value of the

ADT7483A is unknown or not the desired value, it

is first necessary to set it to the correct value

before data can be read from the desired data

register. This is done by performing a write to the

ADT7483A as before, but only the data byte

containing the register read address is sent, as data

is not to be written to the register (see Figure 16).

A read operation is then performed consisting of

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

by the data byte read from the data register (see

Figure 17).

2. 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 and the bus

transaction shown in Figure 16 can be omitted.

NOTES:It is possible to read a data byte from a data register without

first writing to the address pointer register. However, 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.

Remember that some of the ADT7483A registers have

different 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 may not be

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.

ALERT Output

This is applicable when Pin 13 is configured as an ALERT

output. The ALERT output goes low whenever an

out-of-limit measurement is detected, or if the remote

temperature sensor is open circuit. It is an open-drain output

and requires a pull-up to VDD. Several ALERT outputs can

be wire-OR’ed 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 can be used as an SMBALERT. Slave devices

on the SMBus cannot normally signal to the bus master that

they want to talk, but the SMBALERT function allows them

to do so.

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

following procedure occurs, as shown in Figure 18.

MASTER

RECEIVES

SMBALERT

START

ALERT RESPONSE

ADDRESS

RD ACK

DEVICE

ADDRESS

NO

ACK

STOP

MASTER SENDS

ARA AND READ

COMMAND

DEVICE SENDS

ITS ADDRESS

Figure 18. Use of SMBALERT

1. SMBALERT is pulled low.

2. Master initiates a read operation and sends the

alert response address (ARA = 0001 100). This is

a general call address that must not be used as a

specific device address.

3. The device whose ALERT output is low responds

to the alert response address, and the master reads

its device address. The device address is seven

bits, so an LSB of 1 is added. The address of the

device is now known and it can be interrogated in

the usual way.

4. If more than one device’s ALERT output is low,

the one with the lowest device address will have

priority, in accordance with normal SMBus

arbitration.

5. Once the ADT7483A has responded to the alert

response address, it will reset its ALERT output,

provided that the error condition that caused the

ALERT no longer exists. If the SMBALERT line

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