ADT7476
2.914 s
1.457 s
2.914 s
1.457 s
THERM LIMIT
(REG. 0x7A)
728.32 ms
364.16 ms
182.08 ms
91.04 ms
45.52 ms
22.76 ms
0 1 2 3 4 5 6 7
7 6 5 4 3 2 1 0
728.32 ms
364.16 ms
182.08 ms
91.04 ms
45.52 ms
22.76 ms
THERM TIMER
(REG. 0x79)
THERM
THERM TIMER CLEARED ON READ
COMPARATOR
IN OUT
LATCH
RESET
CLEARED
ON READ
F4P BIT (BIT 5)
INTERRUPT STATUS
REGISTER 2
1 = MASK
F4P BIT (BIT 5)
SMBALERT
MASK REGISTER 2
(REG. 0x75)
Figure 33. Functional Block Diagram of THERM Monitoring Circuitry
Configuring the Relevant THERM Behavior
1. Configure the desired pin as the THERM timer
input.
Setting Bit 1 (THERM timer enable) of
Configuration Register 3 (0x78) enables the
THERM timer monitoring functionality. This is
disabled on Pin 14 and Pin 22 by default.
Setting Bit 0 and Bit 1 (PIN14FUNC) of
Configuration Register 4 (0x7D) enables THERM
timer output functionality on Pin 22 (Bit 1 of
Configuration Register 3, THERM, must also be
set). Pin 14 can also be used as TACH4.
2. Select the desired fan behavior for THERM timer
events.
Assuming the fans are running, setting Bit 2
(BOOST bit) of Configuration Register 3 (0x78)
causes all fans to run at 100% duty cycle whenever
THERM is asserted. This allows fail-safe system
cooling. If this bit is 0, the fans run at their current
settings and are not affected by THERM events. If
the fans are not already running when THERM
is asserted, then the fans do not run to full speed.
3. Select whether THERM timer events should
generate SMBALERT interrupts.
Setting Bit 5 (F4P) of Mask Register 2 (0x75) or
Bit 0 of Mask Register 1 (0x74), depending on
which pins are configured as a THERM timer,
masks SMBALERTs when the THERM timer limit
value is exceeded. This bit should be cleared if
SMBALERTs based on THERM events are
required.
4. Select a suitable THERM limit value.
This value determines whether an SMBALERT is
generated on the first THERM assertion, or if only
a cumulative THERM assertion time limit is
exceeded. A value of 0x00 causes a n SMBALERT
to be generated on the first THERM assertion.
5. Select a THERM monitoring time.
This value specifies how often OS- or BIOS-level
software checks the THERM timer. For example,
BIOS can read the THERM timer once an hour to
determine the cumulative THERM assertion time.
If, for example, the total THERM assertion time is
<22.76 ms in Hour 1, >182.08 ms in Hour 2, and
>5.825 sec in Hour 3, system performance is
degrading significantly because THERM is
asserting more frequently on an hourly basis.
Alternatively, OS or BIOS level software can
timestamp when the system is powered on. If an
SMBALERT is generated due to the THERM
timer limit being exceeded, another timestamp can
be taken. The difference in time can be calculated
for a fixed THERM timer limit time. For example,
if it takes one week for a THERM timer limit of
2.914 sec to be exceeded, and the next time it takes
only 1 hour, then a serious degradation in system
performance has occurred.
Configuring the THERM Pin as an Output
In addition to monitoring T HERM as an input, the
ADT7476 can optionally drive THERM low as an output.
When PROCHOT is bidirectional, THERM can be used to
throttle the processor by asserting PROCHOT. The user can
preprogram system-critical thermal limits. If the temperature
exceeds a thermal limit by 0.25 ° C, THERM asserts low. If the
temperature is still above the thermal limit on the next
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