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ADT7516/ADT7517/ADT7519

Rev. A | Page 43 of 44

SMBus/SPI INT/INT

The ADT7516/ADT7517/ADT7519 INT/INT outputs are an

interrupt line for devices that want to trade their ability to

master for an extra pin. The ADT7516/ADT7517/ADT7519 are

slave devices and use the SMBus/SPI INT/INT to signal the host

device that it wants to talk to. The SMBus/SPI INT/INT on the

ADT7516/ADT7517/ADT7519 is used as an over/under limit

indicator.

The INT/INT pin has an open-drain configuration that allows

the outputs of several devices to be wired-AND together when

the INT/INT pin is active low. Use C6 of the Control Config-

uration 1 register to set the active polarity of the INT/INT out-

put. The power-up default is active low. The INT/INT output

can be disabled or enabled by setting C5 of the Control Config-

uration 1 register to 1 or 0, respectively.

The INT/INT output becomes active when either the internal

temperature value, the external temperature value, VDD value, or

any of the AIN input values exceed the values in their corres-

ponding THIGH/VHIGH or TLOW/VLOW registers. The INT/INT out-

put goes inactive again when a conversion result has the mea-

sured value back within the trip limits and when the status reg-

ister associated with the out-of-limit event is read. The two

interrupt status registers show which event caused the INT/INT

pin to go active.

The INT/INT output requires an external pull-up resistor. This

can be connected to a voltage different from VDD, provided the

maximum voltage rating of the INT/INT output pin is not

exceeded. The value of the pull-up resistor depends on the

application but should be large enough to avoid excessive sink

currents at the INT/INT output, which can heat the chip and

affect the temperature reading.

SMBUS ALERT RESPONSE

The INT/INT pin behaves the same way as an SMBus alert pin

when the SMBus/I2C interface is selected. It is an open-drain

output and requires a pull-up to VDD. Several INT/INT outputs

can be wire-AND together, so that the common line will go low

if one or more of the INT/INT outputs goes low. The polarity of

the INT/INT pin must be set active low for a number of outputs

to be wired-AND together.

The INT/INT output can operate as an SMBALERT function.

Slave devices on the SMBus can not normally signal to the

master that they want to talk, but the SMBALERT function

allows them to do so. SMBALERT is used in conjunction with

the SMBus general call address.

One or more INT/INT 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 68.

SMBALERT pulled low.

Master initiates a read operation and sends the alert res-

ponse address (ARA = 0001 100). This is a general call

address that must not be used as a specific device address.

The devices whose INT/INT output is low responds to the

alert response address and the master reads its device

address. As the device address is seven bits long, 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 INT/INT output is low, the one

with the lowest device address will have priority in accor-

dance with normal SMBus specifications.

Once the ADT7516/ADT7517/ADT7519 have responded

to the alert response address, they will reset their INT/INT

output, provided that the condition that caused the out-of-

limit event no longer exists and that the status register

associated with the out-of-limit event is read. If the

SMBALERT line remains low, the master will send the

ARA again. It will continue to do this until all devices

whose SMBALERT outputs were low have responded.

MASTER

RECEIVES

SMBALERT

START

ALERT RESPONSE

ADDRESS

RD ACK DEVICE ADDRESS

MASTER SENDS

ARA AND READ

COMMAND

DEVICE SENDS

ITS ADDRESS

ACK

STOP

Figure 68. INT/INT Responds to SMBALERT ARA

MASTER

RECEIVES

SMBALERT

START

ALERT RESPONSE

ADDRESS

RD ACK

DEVICE

ADDRESS

MASTER SENDS

ARA AND READ

COMMAND

DEVICE SENDS

ITS ADDRESS

DEVICE ACK

ACK

PEC

ACK

STOP

MASTER

ACK

MASTER

NACK

DEVICE SENDS

ITS PEC DATA

Figure 69. INT/INT Responds to SMBALERT ARA

with Packet Error Checking (PEC)

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