ADT7461ARM datasheet(16/24 Pages) AD

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ADT7461

ALERT RESPONSE

ADDRESS

MASTER SENDS

ARA AND READ

COMMAND

DEVICE SENDS

ITS ADDRESS

START

ACK

DEVICE

ADDRESS

ACK STOP

MASTER

RECEIVES

SMBALERT

When reading data from a register there are two possibilities:

•

If the ADT7461’s address pointer register value 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

ADT7461 as before, but only the data byte containing the

the register. This is shown in F

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. This is shown in

igure 16

Figure 17

•

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

can be

omitted.

Notes

Although it is possible to read a data byte from a data

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.

Do not forget that some of the ADT7461 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 6 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-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 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 illustrated in F

igure 18

Figure 18. 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. As the device address is seven bits, 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 accor-

dance with normal SMBus arbitration.

Once the ADT7461 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.

LOW POWER STANDBY MODE

The ADT7461 can be put into low power standby mode by

setting Bit 6 of the configuration register. When Bit 6 is low, the

ADT7461 operates normally. When Bit 6 is high, 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 10 µA if there is no SMBus activity

or 100 µA if there are clock and data signals on the bus.

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 0×0F), after which the device will return

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

write new values to the limit register while in standby mode. If

the values stored in the temperature value registers are now

outside the new limits, an ALERT is generated, even though the

ADT7461 is still in standby.

SENSOR FAULT DETECTION

The ADT7461 has sensor fault detection circuitry internally at

its D+ input. This circuit can detect situations where an external

remote diode is not connected, or is incorrectly connected, to

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