ADT7483AARQZ-R7 datasheet(19/24 Pages) ONSEMI

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ADT7483A

Rev. 1 | Page 19 of 24 | www.onsemi.com

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 19.

ALERT RESPONSE

ADDRESS

MASTER SENDS

ARA AND READ

COMMAND

DEVICE SENDS

ITS ADDRESS

START

ACK

DEVICE

ADDRESS

ACK STOP

MASTER

RECEIVES

SMBALERT

Figure 19. Use of SMBALERT

SMBALERT is pulled low.

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.

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.

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.

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 remains low, the master will send the

ARA again, and so on, until all devices whose ALERT outputs

were low have responded.

MASKING THE ALERT OUTPUT

The ALERT output can be masked for local, Remote 1,

Remote 2, or all three channels. This is done by setting the

appropriate mask bits in either the Configuration 1 register

(read address = 0x03, write address = 0x09) or in the

consecutive ALERT register (address = 0x22)

To mask ALERTs due to local temperature, set Bit 5 of the

consecutive ALERT register to 1. Default = 0.

To mask ALERTs due to Remote 1 temperature, set Bit 1 of the

Configuration 1 register to 1. Default = 0.

To mask ALERTs due to Remote 2 temperature, set Bit 0 of the

Configuration 1 register to 1. Default = 0.

To mask ALERTs due to any channel, set Bit 7 of the

Configuration 1 register to 1. Default = 0.

LOW POWER STANDBY MODE

The ADT7483A can be put into low power standby mode by

setting Bit 6 (Mon/STBY bit) of the Configuration 1 register

(read address = 0x03, write address = 0x09) to 1. When Bit 6 is

0, the ADT7483A operates normally. When Bit 6 is 1, the ADC

is inhibited, and any conversion in progress is terminated

without writing the result to the corresponding value register.

The SMBus is still enabled. Power consumption in the standby

mode is reduced to less than 5 μA.

When the device is in standby mode, it is still possible to initiate

a one-shot conversion of both channels by writing to the one-

shot register (Address 0x0F), after which the device will return

to standby. It does not matter what is written to the one-shot

It is also possible to write new values to the limit register while

in standby mode. If the values stored in the temperature value

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