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INTERRUPT

OVR Pin

OVR

OVREN

AMC6821

Output

Latch

Set

Reset

LTCBit

(Localtemperaturereachesthecritcalshutdownthreshold.)

LocalTemperature<(Local-Critical-Temp

5 C)

- °

Output

Latch

Set

Reset

RTCBit

(Remotetemperaturereachesthecritcalshutdownthreshold.)

RemoteTemperature<(Remote-Critical-Temp

5 C)

- °

RTF

(RemoteTemperatureSensorFailure)

SMBALERT Pin

SMBALERT Interrupt Behavior

AMC6821

SBAS386C – MAY 2006 – REVISED JULY 2007

The AMC6821 provides two interrupt output pins, OVR and SMBALERT.

OVR is an open-drain output pin that works as an over-critical temperature limit (shutdown threshold) indicator

and remote sensor failure indicator. This architecture is shown in Figure 30. Setting the OVREN bit of

Configuration Register 4 to '1' enables this pin; clearing OVREN ('0') disables it. When disabled, the OVR pin is

in a high-impedance status. When enabled, the status is controlled by the over-critical temperature flag and

remote sensor failure flag bits of the Status Registers.

When the temperature is over the critical limit (shutdown threshold), the corresponding over-critical limit flag of

the Status Register (RTC for the remote channel and LTC for the local channel) is set ('1'). This flag is cleared

('0') when reading the Status Registers. Once cleared, this bit is not reasserted until the temperature falls 5

°C

below the exceeded critical limit, even if the over-critical limit condition persists. When the temperature is equal to

or above the critical temperature limit, the OVR pin is asserted (active low) to indicate this critical condition. As

the over-critical temperature limit indicator, the OVR pin remains low once asserted until the measured

temperature falls 5

°C below the exceeded critical limit.

Figure 30. OVR Pin

When a remote temperature sensor failure condition is detected (either short-circuit or open-circuit), the remote

temperature sensor failure bit (RTF) in Status Register 1 (bit 5, 0x02) is set ('1') and the OVR pin is forced low no

matter what the status of RTFIE is. This value indicates a remote sensor failure condition. Once this condition

occurs, the RTF bit remains '1' and the OVR pin stays low until a power-on reset or software reset is issued,

regardless if the failure condition continues thereafter. RTF = 1 also generates an RTF interrupt through the

SMBALERT pin when RTFIE = 1.

The SMBALERT pin is a standard interrupt output defined by SMBus specification revision 2.0. This pin is an

open-drain output pin and is illustrated in Figure 33.

When an out-of-limit event occurs, the proper flag bits in the status registers are set ('1'), and the corresponding

interrupts are generated, if enabled. When an interrupt is generated, the SMBALERT pin asserts low. The host

can poll the device status registers to get the information, or give a response to the SMBALERT interrupt signal.

It is important to note how the SMBALERT output and status bits behave when writing interrupt-handler software.

Figure 31 shows how the SMBALERT output and status bits behave.

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