adm1027 Analog Devices, Inc., adm1027 Datasheet - Page 19

• Manufacturer Part Number: adm1027
• Description: Dbcool? Remote Thermal Controller And Voltage Monitor
• Manufacturer: Analog Devices, Inc.

SMBALERT INTERRUPT BEHAVIOR
The ADM1027 can be polled for status, or an SMBALERT
interrupt can be generated for out-of-limit conditions. It is
important to note how the SMBALERT output and status bits
behave when writing interrupt handler software.
Figure 16 shows how the SMBALERT output and sticky status
bits behave. Once a limit is exceeded, the corresponding status
bit is set to 1. The status bit remains set until the error condition
subsides and the status register is read. The status bits are referred
to as sticky since they remain set until read by software. This
ensures that an out-of-limit event cannot be missed if software
is polling the device periodically. Note that the SMBALERT
output remains low for the entire duration that a reading is
out-of-limit and until the status register has been read. This has
implications on how software handles the interrupt.
HANDLING SMBALERT INTERRUPTS
To prevent the system from being tied up servicing interrupts,
it is recommend to handle the SMBALERT interrupt as follows:
1. Detect the SMBALERT assertion.
2. Enter the interrupt handler.
3. Read the status registers to identify the interrupt source.
4. Mask the interrupt source by setting the appropriate mask bit
5. Take the appropriate action for a given interrupt source.
6. Exit the interrupt handler.
7. Periodically poll the status registers. If the interrupt status bit
REV. A
TEMPERATURE
in the interrupt mask registers (Reg. 0x74, 0x75).
has cleared, reset the corresponding interrupt mask bit to 0.
This will cause the SMBALERT output and status bits to
behave as shown in Figure 17.
SMBALERT
HIGH LIMIT
STATUS
Figure 16. SMBALERT and Status Bit Behavior
STICKY
BIT
TEMP BACK IN LIMIT
(STATUS BIT STAYS SET)
CLEARED ON READ
(TEMP BELOW LIMIT)
–19–
MASKING INTERRUPT SOURCES
Interrupt Mask Registers 1 and 2 are located at Addresses 0x74
and 0x75. These allow individual interrupt sources to be masked
out to prevent SMBALERT interrupts. Note that masking an
interrupt source prevents only the SMBALERT output from
being asserted; the appropriate status bit will be set as normal.
INTERRUPT MASK REGISTER 1 (REG. 0x74)
Bit 7 (OOL) = 1, set this bit to 1 to allow masking of interrupts
by Status Register 2. If this bit = 0, then setting a bit in Mask
Register 2 to 1 will have no effect.
Bit 6 (R2T) = 1, masks SMBALERT for Remote 2 temperature.
Bit 5 (LT) = 1, masks SMBALERT for local temperature.
Bit 4 (R1T) = 1, masks SMBALERT for Remote 1 temperature.
Bit 3 (5 V) = 1, masks SMBALERT for 5 V channel.
Bit 2 (V
Bit 1 (V
Bit 0 (2.5 V) = 1, masks SMBALERT for 2.5 V channel.
INTERRUPT MASK REGISTER 2 (REG. 0x75)
Bit 7 (D2) = 1, masks SMBALERT for Diode 2 errors.
Bit 6 (D1) = 1, masks SMBALERT for Diode 1 errors.
Bit 5 (FAN4) = 1, masks SMBALERT for Fan 4.
Bit 4 (FAN3) = 1, masks SMBALERT for Fan 3.
Bit 3 (FAN2) = 1, masks SMBALERT for Fan 2.
Bit 2 (FAN1) = 1, masks SMBALERT for Fan 1.
Bit 1 (OVT) = 1, masks SMBALERT for overtemperature
(exceeding THERM limits).
Bit 0 (12 V) = 1, masks SMBALERT for 12 V channel.
TEMPERATURE
SMBALERT
HIGH LIMIT
STATUS
STICKY
Figure 17. How Masking the Interrupt Source
Affects SMBALERT Output
CC
CCP
BIT
) = 1, masks SMBALERT for V
) = 1, masks SMBALERT for V
TEMP BACK IN LIMIT
(STATUS BIT STAYS SET)
INTERRUPT
MASK BIT SET
CC
CCP
INTERRUPT MASK
BIT CLEARED
(SMBALERT REARMED)
ADM1027
channel.
CLEARED ON READ
(TEMP BELOW LIMIT)
channel.