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ADM1026JSTZ View Datasheet(PDF) - Analog Devices

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ADM1026JSTZ Datasheet PDF : 56 Pages
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Status Register 4 also stores inputs from two other interrupt
sources that operate in a different way from the other status bits.
If automatic fan speed control (AFC) is enabled, Bit 4 of Status
Register 4 is set whenever a fan starts or stops. This bit causes a
one-off INT output as shown in Figure 52. It is cleared during
the next monitoring cycle and if INT has been cleared, it does
not cause INT to be reasserted.
FAN ON
FAN OFF
INT
INT CLEARED BY STATUS REGULAR 1 READ, BIT 2
OF CONFIGURATION REGULAR 1 SET, OR ARA
Figure 52. Assertion of INT Due to AFC Event
In a similar way, a change of state at the THERM output
(described in more detail later), sets Bit 3 of Status
Register 4 and causes a one-off INT output. A change of state at
the THERM output also causes Bit 0 of Status Register 1, Bit 1
of Status Register 1, or Bit 0 of Status Register 4 to be set,
depending on which temperature channel caused the THERM
event. This bit is reset during the next monitoring cycle,
provided the temperature channel is within the normal high
and low limits.
Fan Inputs
Fan inputs generate interrupts in a similar way to analog/
temperature inputs, but as the analog/ temperature inputs and
fan inputs have different monitoring cycles, they have separate
interrupt circuits. As the speed of each fan is measured, the
output of the fan speed counter is stored in a value register. The
result is compared to the fan speed limit and is used to set or
clear a bit in Status Register 3. In this case, the fan is monitored
only for under-speed (fan counter > fan speed limit). Mask
Register 3 is used to mask fan interrupts. After mask gating, the
fan status bits are OR’ed together and used to set a latch, whose
output is OR’ed with other interrupt sources to produce the INT
output.
Like the analog/temp interrupt, an INT output caused by an
out-of-limit fan speed measurement, once cleared, is not
reasserted until the end of the next monitoring cycle, although
other interrupt sources may cause INT to be asserted.
GPIO and CI Pins. When GPIO pins are configured as inputs,
asserting a GPIO input (high or low, depending on polarity) sets
the corresponding GPIO status bit in Status Registers 5 and 6, or
Bit 7 of Status Register 4 (GPIO16). A chassis intrusion event
sets Bit 6 of Status Register 4.
ADM1026
The GPIO and CI status bits, after mask gating, are OR’ed
together and OR’ed with other interrupt sources to produce the
INT output. GPIO and CI interrupts are not latched and cannot
be cleared by normal interrupt clearing. They can only be
cleared by masking the status bits or by removing the source of
the interrupt.
ENABLING AND CLEARING INTERRUPTS
The INT output is enabled when Bit 1 of Configuration
Register 1 (INT_Enable) is high, and Bit 2 (INT_Clear) is low.
INT may be cleared if
Status Register 1 is read. Ideally, if polling the status
registers trying to identify interrupt sources, Status
Register 1 should be polled last, because a read of Status
Register 1 clears all the other interrupt status registers.
The ADM1026 receives the alert response address (ARA)
(0001 100) over the SMBus.
Bit 2 of Configuration Register 1 is set.
Bidirectional THERM Pin
The ADM1026 has a second interrupt pin (GPIO16/THERM
Pin 42) that responds only to critical thermal events. The
THERM pin goes low whenever a THERM limit is exceeded.
This function is useful for CPU throttling or system shutdown.
In addition, whenever THERM is activated, the PWM and DAC
outputs go full scale to provide fail-safe system cooling. This
output is enabled by setting Bit 4 of Configuration Register 1
(Register 00h). Whenever a THERM limit is exceeded, Bit 3 of
Status Register 4 (Reg 23h) is set, even if the THERM function
is disabled (Bit 4 of Configuration Register 1 = 0). In this case,
the THERM status bit is set, but the PWM and DAC outputs are
not forced to full scale.
Three thermal limit registers are provided for the three
temperature sensors at Addresses 0Dh to 0Fh. These registers
are dedicated to the THERM function and none of the other
limit registers have any effect on the THERM output.
If any of the temperature measurements exceed the correspond-
ing limit, THERM is asserted (low) and the DAC and PWM
outputs go to maximum to drive any cooling fans to full speed.
To avoid cooling fans cycling on and off continually when the
temperature is close to the limit, a fixed hysteresis of 5°C is
provided. THERM is only deasserted when the measured
temperature of all three sensors is 5°C below the limit.
Whenever the THERM output changes, INT is asserted, as
shown in Figure 54. However, this is edge-triggered, so if INT
is subsequently cleared by one of the methods previously
described, it is not reasserted, even if THERM remains asserted.
THERM causes INT to be reasserted only when it changes state.
Rev. A | Page 29 of 56
 

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