Datasheet

ADT7316/ADT7317/ADT7318
Rev. B | Page 40 of 44
SMBUS/SPI INT/
INT
The ADT7316/ADT7317/ADT7318 INT/
INT
output is an
interrupt line that signals an over-limit/under-limit event on
any of the measurement channels if the interrupt on that event
has not been disabled. The ADT7316/ADT7317/ADT7318 are
slave-only devices and use the SMBus/SPI INT/
INT
as their
only means to signal other devices that an event has occurred.
The INT/
INT
pin has an open-drain configuration that allows
the outputs of several devices to be wire-AND’ed together when
the INT/
INT
pin is active low. Use C6 of the Control Configu-
ration 1 register (Address 0x18) to set the active polarity of the
INT/
INT
output. The power-up default is active low. The INT/
INT
output can be disabled or enabled by setting C5 of the
Control Configuration 1 register (Address 0x18) to 1 or 0,
respectively.
The INT/
INT
output becomes active when either the internal
temperature value, the external temperature value, or the V
DD
value exceeds the values in their corresponding T
HIGH
/V
HIGH
or
T
LOW
/V
LOW
registers. The INT/
INT
output goes inactive again
when a conversion result indicates that all measurement channels
are within their trip limits, and when the status register associ-
ated 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 V
DD
provided that
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 a SMBus alert pin
when the SMBus/I
2
C interface is selected. It is an open-drain
output and requires a pull-up to V
DD
. Several INT/
INT
outputs
can be wire-AND’ed together so that the common line goes low
if one or more of the INT/
INT
outputs goes low. The polarity
of the INT/
INT
pin must be set for active low for a number of
outputs to be wire-AND’ed together. The INT/
INT
output can
operate as a
SMBALERT
function. Slave devices on the SMBus
typically cannot 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 a
SMBALERT
line is pulled low by one of the devices, the following procedure
occurs (see Figure 59).
MASTER
RECEIVES
SMBALERT
START
ALERT RESPONSE
ADDRESS
RD ACK DEVICE ADDRESS
MASTER SENDS
ARA AND READ
COMMAND
DEVICE SENDS
ITS ADDRESS
NO
ACK
STOP
0
2661-059
Figure 59. INT/
INT
Responds to
SMBALERT
ARA
1.
SMBALERT
is pulled low.
2. The mast
er 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 de
vices whose INT/
INT
output is low respond to the
alert response address and the master reads its device
address. Because the device address is 7 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 devices INT/
INT
output is low, the one
with the lowest device address has priority, in accordance
with typical SMBus specifications.
5. On
ce the ADT7316/ADT7317/ADT7318 has responded
to the alert response address, it resets its INT/
INT
output,
provided that the condition that caused the out-of-limit
event no longer exists and the status register associated with
the out-of-limit event is read. If the
SMBALERT
line remains
low, the master sends the ARA again. It continues 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
DEVICE ACK
ACK PEC
NO
ACK
STOP
MASTER
ACK
MASTER
NACK
DEVICE SENDS
ITS PEC DATA
0
2661-060
Figure 60. INT/
INT
Responds to
SMBALERT
ARA with
Packet Error Checking (PEC)