ADT75BRMZ-REEL7(RevB) 查看數據表（PDF） - Analog Devices
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ADT75BRMZ-REEL7 Datasheet PDF : 24 Pages
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ADT75
SMBus ALERT
The OS/ALERT pin can behave as a SMBus alert pin when the
SMBus alert function is enabled by setting Bit D7 in the
configuration register. The interrupt mode must also be selected
(Bit D1 in the configuration register). The OS/ALERT pin is an
open-drain output and requires a pull-up to VDD. Several SMBus
alert outputs can be wire-AND’ed together, so that the common
line goes low if one or more of the SMBus alert outputs goes
low. The polarity of the OS/ALERT pin must be set for active
low for a number of outputs to be wire-AND’ed together.
The OS/ALERT output can operate as a SMBALERT function.
Slave devices on the SMBus normally 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 SMBus 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 20.
MASTER
RECEIVES
SMBALERT
START
ALERT RESPONSE
ADDRESS
RD
ACK
DEVICE ADDRESS
NO
ACK
STOP
MASTER SENDS
ARA AND READ
COMMAND
DEVICE SENDS
ITS ADDRESS
Figure 20. ADT75 Responds to SMBALERT ARA
Data Sheet
1. SMBALERT is pulled low.
2. Master initiates a read operation and sends the SMBus alert
response address (ARA = 0001 100). This reserved SMBus/
I2C address must not be used as a specific device address.
3. The device whose SMBus alert output is low responds to the
SMBus alert response address and the master reads its device
address. As the device address is seven bits long, the ADT75’s
LSB is free to be used as an indicator as to which temperature
limit was exceeded. The LSB is high if the temperature is
greater than or equal to TOS, and the LSB is low if the
temperature is less than THYST. The address of the device
is now known and it can be interrogated in the usual way.
4. If more than one devices’ SMBus alert output is low, the one
with the lowest device address has priority, which is in
accordance with normal SMBus specifications.
Once the ADT75 has responded to the SMBus alert response
address, it resets its SMBus alert output. 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
DEVICE ACK
MASTER
ACK
MASTER
NACK
START
ALERT RESPONSE
ADDRESS
RD
ACK
DEVICE
ADDRESS
ACK
PEC
NO
ACK
STOP
MASTER SENDS
ARA AND READ
COMMAND
DEVICE SENDS DEVICE SENDS
ITS ADDRESS ITS PEC DATA
Figure 21. ADT75 Responds to SMBALERT ARA with
Packet Error Checking (PEC)
Rev. B | Page 20 of 24
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