Datasheet

Remote High Limit
Remote Diode
Measurement
Time
Temperature
ALERT mask set in
response to reading of
status register by master
LM96163
ALERT pin
Status Register: Remote High
End of Temperature
conversion
Voltage
LM96163
SNAS433D –JUNE 2008–REVISED MAY 2013 www.ti.com
Figure 9. ALERT Output as an Interrupt Temperature Response Diagram
ALERT Output as an SMBus ALERT
An SMBus alert line is created when the ALERT output is connected to: (1) one or more ALERT outputs of other
SMBus compatible devices, and (2) to a master. Under this implementation, the LM96163's ALERT should be
operated using the ARA (Alert Response Address) protocol. The SMBus 2.0 ARA protocol, defined in the SMBus
specification 2.0, is a procedure designed to assist the master in determining which part generated an interrupt
and to service that interrupt.
The SMBus alert line is connected to the open-drain ports of all devices on the bus, thereby AND'ing them
together. The ARA method allows the SMBus master, with one command, to identify which part is pulling the
SMBus alert line LOW. It also prevents the part from pulling the line LOW again for the same triggering condition.
When an ARA command is received by all devices on the bus, the devices pulling the SMBus alert line LOW: (1)
send their address to the master and (2) release the SMBus alert line after acknowledgement of their address.
The SMBus Specifications 1.1 and 2.0 state that in response to and ARA (Alert Response Address) “after
acknowledging the slave address the device must disengage its ALERT pulldown”. Furthermore, “if the host still
sees ALERT low when the message transfer is complete, it knows to read the ARA again.” This SMBus
“disengaging ALERT requirement prevents locking up the SMBus alert line. Competitive parts may address the
“disengaging of ALERT” differently than the LM96163 or not at all. SMBus systems that implement the ARA
protocol as suggested for the LM96163 will be fully compatible with all competitive parts.
The LM96163 fulfills “disengaging of ALERT” by setting the ALERT Mask Bit in the Configuration Register after
sending out its address in response to an ARA and releasing the ALERT output pin. Once the ALERT Mask bit is
activated, the ALERT output pin will be disabled until enabled by software. In order to enable the ALERT the
master must read the ALERT Status Register, during the interrupt service routine and then reset the ALERT
Mask bit in the Configuration Register to 0 at the end of the interrupt service routine.
The following sequence describes the ARA response protocol.
1. Master senses SMBus alert line low
2. Master sends a START followed by the Alert Response Address (ARA) with a Read Command.
3. Alerting Device(s) send ACK.
4. Alerting Device(s) send their address. While transmitting their address, alerting devices sense whether their
address has been transmitted correctly. (The LM96163 will reset its ALERT output and set the ALERT Mask
bit once its complete address has been transmitted successfully.)
5. Master/slave NoACK
6. Master sends STOP
7. Master attends to conditions that caused the ALERT to be triggered. The ALERT Status Register is read and
fan started, setpoints adjusted, etc.
8. Master resets the ALERT Mask bit in the Configuration Register.
The ARA, 000 1100, is a general call address. No device should ever be assigned to this address.
The ALERT Configuration bit in the Remote Diode Temperature Filter and Comparator Mode Register must be
set low in order for the LM96163 to respond to the ARA command.
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