ADT7470 Analog Devices, Inc., ADT7470 Datasheet - Page 17

• Manufacturer Part Number: ADT7470
• Description: Temperature Sensor Hub And Fan Controller
• Manufacturer: Analog Devices, Inc.

TEMPERATURE
Table 11. Interrupt Status Register 2 (Register 0x42)
Bit No.
<7>
<6>
<5>
<4>
<3>
<2>
<1>
<0>
SMBALERT INTERRUPT BEHAVIOR
The ADT7470 can be polled for status, or an SMBALERT
interrupt can be generated for out-of-limit conditions. Note
how the SMBALERT output and status bits behave when
writing interrupt handler software.
Figure 21 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 because they remain set until read by soft-
ware. This ensures that an out-of-limit event cannot be missed
if software is polling the device periodically. The SMBALERT
output remains low for the duration that a reading is out of limit
until the status register is read. This has implications for how
software handles the interrupt.
SMBALERT
HIGH LIMIT
"STICKY"
STATUS
BIT
Figure 21. SMBALERT and Status Bit Behavior
Mnemonic
Fan 4
Fan 3
Fan 2
Fan 1
NORM
R10T
R9T
R8T
TEMP BACK IN LIMIT
(STATUS BIT STAYS SET)
Description
A 1 indicates that Fan 4 has dropped below minimum speed or is above maximum speed.
A 1 indicates that Fan 3 has dropped below minimum speed or is above maximum speed.
A 1 indicates that Fan 2 has dropped below minimum speed or is above maximum speed.
A 1 indicates that Fan 1 has dropped below minimum speed or is above maximum speed.
A 1 indicates that the temperatures are below T
A 1 indicates that TMP05 Temperature 10 high or low limit has been exceeded.
A 1 indicates that TMP05 Temperature 9 high or low limit has been exceeded.
A 1 indicates that TMP05 Temperature 8 high or low limit has been exceeded.
CLEARED ON READ
(TEMP BELOW LIMIT)
Figure 20. Interrupt Status Register 2
F4P = 1, FAN4 OR PROCHOT
Rev. B | Page 17 of 40
TIMER IS OUT-OF-LIMIT
HANDLING SMBALERT INTERRUPTS
To prevent the system from being tied up servicing interrupts,
handle the SMBALERT interrupt as follows:
1.
2.
3.
4.
5.
6.
7.
TEMPERATURE
Figure 22. How Masking the Interrupt Source Affects SMBALERT Output
SMBALERT
HIGH LIMIT
"STICKY"
Detect the SMBALERT assertion.
Enter the interrupt handler.
Read the status registers to identify the interrupt source.
Mask the interrupt source by setting the appropriate mask
bit in the interrupt mask registers (Register 0x72 and
Register 0x73).
Take the appropriate action for a given interrupt source.
Exit the interrupt handler.
Periodically poll the status registers. If the interrupt status
bit is cleared, reset the corresponding interrupt mask bit
to 0. This causes the SMBALERT output and status bits
to behave as shown in Figure 22.
STATUS
MIN
BIT
and that the fans are supposed to be off.
TEMP BACK IN LIMIT
(STATUS BIT STAYS SET)
INTERRUPT
MASK BIT SET
(SMBALERT RE-ENABLED)
INTERRUPT MASK BIT
(TEMP BELOW LIMIT)
CLEARED ON READ
CLEARED
ADT7470