LM64 datasheet(13/42 Pages) TI2

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Remote High Limit

RDTS Measurement

LM64 ALERT Pin

Status Register: RTDS High

TIME

Figure 6-2. ALERT Output as Temperature Comparator Response Diagram

6.3.2.2 ALERT Output as an Interrupt

The LM64's ALERT output can be implemented as a simple interrupt signal when it is used to trigger an interrupt

service routine. In such systems it is desirable for the interrupt flag to repeatedly trigger during or before the

interrupt service routine has been completed. Under this method of operation, during the read of the ALERT

Status Register the LM64 will set the ALERT Mask bit in the Configuration Register if any bit in the ALERT

Status Register is set, with the exception of Busy and Open. This prevents further ALERT triggering until the

master has reset the ALERT Mask bit, at the end of the interrupt service routine. The ALERT Status Register

bits are cleared only upon a read command from the master (see Figure 6-2) and will be re-asserted at the

end of the next conversion if the triggering condition(s) persist(s). In order for the ALERT to be used as a

dedicated interrupt signal, the Comparator Mode bit in the Remote Diode Temperature Filter and Comparator

Mode Register must be set low. This is the power-on default state. The following sequence describes the

response of a system that uses the ALERT output pin as an interrupt flag:

1. Master senses ALERT low.

2. Master reads the LM64 ALERT Status Register to determine what caused the ALERT.

3. LM64 clears ALERT Status Register, resets the ALERT HIGH and sets the ALERT Mask bit in the

Configuration Register.

4. Master attends to conditions that caused the ALERT to be triggered. The fan is started, setpoint limits are

adjusted, etc.

5. Master resets the ALERT Mask bit in the Configuration Register.

Remote High Limit

RDTS Measurement

TIME

ALERT mask set in

response to reading of

status register by master

LM64

ALERT pin

Status Register: RTDS High

End of Temperature

conversion

Figure 6-3. ALERT Output as an Interrupt Temperature Response Diagram

6.3.2.3 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 LM64'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.

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LM64

SNAS207B – MAY 2004 – REVISED JANUARY 2024

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