SA56004X_5

© NXP B.V. 2008. All rights reserved.

Product data sheet

Rev. 05 — 22 May 2008

12 of 36

NXP Semiconductors

SA56004X

Digital temperature sensor with overtemperature alarms

7.9 Interruption logic and functional description

7.9.1 ALERT output

The ALERT output is used to signal Alert interruptions from the device to the SMBus or

other system interrupt handler and it is active LOW. Because this is an open-drain output,

a pull-up resistor (typically 10 k

Ω) to V

common interrupt line on the same SMBus.

The ALERT function is very versatile and accommodates three separate operating

modes:

The ARA and interrupt modes are different only in how the user interacts with the

SA56004X.

At the end of every temperature reading, digital comparators determine if the readings are

above the HIGH or T_CRIT setpoint or below the LOW setpoint register values. If so, the

corresponding bit in the Status register is set. If the ALERT mask bit 7 of the Configuration

register is not HIGH, then any bit set in the Status register other than the BUSY (D7) and

OPEN (D2) will cause the ALERT output pin to be active LOW. An alert will be triggered

after any conversion cycle that finds the temperature is out of the limits defined by the

setpoint registers. In order to trigger an ALERT in all alert modes, the ALERT mask bit 7 of

the Configuration register must be cleared (not HIGH).

7.9.1.1

ALERT output in comparator mode

When operating the SA56004X in a system that utilizes an SMBus controller not having

an interrupt, the ALERT output may be operated as a temperature comparator. In this

mode, when the condition that triggered the ALERT to be asserted is no longer present,

the ALERT output is released as it goes HIGH. In order to use the ALERT output as a

temperature comparator, bit D0 (the ALERT configure bit) in the ALERT Mode (AM)

register must be set HIGH. This is not the POR default.

7.9.1.2

ALERT output in interrupt mode

In the interrupt mode, the ALERT output is used to provide an interrupt signal that remains

asserted until the interrupt service routine has elapsed. In the interrupt operating mode, a

read of the Status register will set the ALERT mask bit 7 of the Configuration register if

any of the temperature alarm bits of the Status register is set, with exception of BUSY

(D7) and OPEN (D2). This protocol prevents further ALERT output triggering until the

master device has reset the ALERT mask bit at the end of the interrupt service routine.

The Status register bits are cleared only upon a read of the Status register by the serial

bus master (see Figure 5). In order for the ALERT output to be used as an interrupt, the

ALERT Configure bit D0 of the ALERT Mode (AM) register must be set LOW (POR

default).