SA56004X Datasheet, PDF (12/36 Pages) NXP Semiconductors – 1 Degrees Celcious accurate, SMBus-compatible, 8-pin, remote/local digital temperature sensor with over temperature alarms

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 kΩ) to V_DD is required. Several slave devices can share a
common interrupt line on the same SMBus.
The ALERT function is very versatile and accommodates three separate operating
modes:
• Temperature comparator
• System interrupt based on temperature
• SMBus Alert Response Address (ARA) response.
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).
SA56004X_5
Product data sheet
Rev. 05 — 22 May 2008
© NXP B.V. 2008. All rights reserved.
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