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ADT7516 Datasheet(PDF) 43 Page - Analog Devices

Part No. ADT7516
Description  SPI/I2C Compatible, Temperature Sensor, Four Channel ADC and Quad Voltage Output DAC
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Maker  AD [Analog Devices]
Homepage  http://www.analog.com
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ADT7516 Datasheet(HTML) 43 Page - Analog Devices

 
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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.
1.
SMBALERT pulled low.
2.
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.
3.
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.
4.
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.
5.
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
NO
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
NO
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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