ADT7475 Analog Devices, Inc., ADT7475 Datasheet - Page 21

• Manufacturer Part Number: ADT7475
• Description: Dbcool Remote Thermal Monitor And Fan Controller
• Manufacturer: Analog Devices, Inc.

As mentioned previously, the ADC performs round-robin
conversions. The total monitoring cycle time for averaged
voltage and temperature monitoring is 146 ms. The total
monitoring cycle time for voltage and temperature moni-
toring with averaging disabled is 19 ms. The ADT7475 is a
derivative of the ADT7467. As a result, the total conversion
time in the ADT7475 is the same as the total conversion time
of the ADT7467.
Fan TACH measurements are made in parallel and are not
synchronized with the analog measurements in any way.
INTERRUPT STATUS REGISTERS
The results of limit comparisons are stored in Interrupt Status
Register 1 and Interrupt Status Register 2. The status register bit for
each channel reflects the status of the last measurement and limit
comparison on that channel. If a measurement is within limits, the
corresponding status register bit is cleared to 0. If the measurement
is out-of-limits, the corresponding status register bit is set to 1.
The state of the various measurement channels can be polled by
reading the status registers over the serial bus. In Bit 7 (OOL) of
Interrupt Status Register 1 (0x41), 1 means that an out-of-limit
event has been flagged in Interrupt Status Register 2. This means
that the user needs only to read Interrupt Status Register 2 when
this bit is set. Alternatively, Pin 5 or Pin 9 can be configured as an
SMBALERT output. This automatically notifies the system
supervisor of an out-of-limit condition. Reading the status
registers clears the appropriate status bit as long as the error
condition that caused the interrupt has cleared.
Status register bits are sticky. Whenever a status bit is set,
indicating an out-of-limit condition, it remains set even if the
event that caused it has gone away (until read). The only way to
clear the status bit is to read the status register after the event
has gone away. Interrupt status mask registers (0x74 and 0x75)
allow individual interrupt sources to be masked from causing
an SMBALERT . However, if one of these masked interrupt
sources goes out-of-limit, its associated status bit is set in the
interrupt status registers.
Interrupt Status Register 1 (0x41)
Bit 7 (OOL) = 1, denotes that a bit in Status Register 2 is set and
that Interrupt Status Register 2 should be read.
Bit 6 (R2T) = 1, Remote 2 temperature high or low limit has
been exceeded.
Bit 5 (LT) = 1, local temperature high or low limit has been
exceeded.
Bit 4 (R1T) = 1, Remote 1 temperature high or low limit has
been exceeded.
Bit 2 (V
Bit 1 (V
CC
CCP
) = 1, V
) = 1, V
CC
CCP
high or low limit has been exceeded.
high or low limit has been exceeded.
Rev. B | Page 21 of 68
Interrupt Status Register 2 (0x42)
Bit 7 (D2) = 1, indicates an open or short on D2+/D2– inputs.
Bit 6 (D1) = 1, indicates an open or short on D1+/D1– inputs.
Bit 5 (F4P) = 1, indicates that Fan 4 has dropped below
minimum speed. Alternatively, indicates that the THERM limit
has been exceeded, if the THERM function is used.
Bit 4 (FAN3) = 1, indicates that Fan 3 has dropped below
minimum speed.
Bit 3 (FAN2) = 1, indicates that Fan 2 has dropped below
minimum speed.
Bit 2 (FAN1) = 1, indicates that Fan 1 has dropped below
minimum speed.
Bit 1 (OVT) = 1, indicates that a THERM overtemperature limit
has been exceeded.
SMBALERT Interrupt Behavior
The ADT7475 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 25 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 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 interrupt status register has been read.
This has implications for how software handles the interrupt.
HIGH LIMIT
TEMPERATURE
STATUS BIT
SMBALERT
STICKY
Figure 25. SMBALERT and Status Bit Behavior
TEMP BACK IN LIMIT
(STATUS BIT STAYS SET)
(TEMP BELOW LIMIT)
CLEARED ON READ
ADT7475