ADT7475 Analog Devices, Inc., ADT7475 Datasheet - Page 20

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

ADT7475
LIMITS, STATUS REGISTERS, AND INTERRUPTS
LIMIT VALUES
Associated with each measurement channel on the ADT7475
are high and low limits. These can form the basis of system
status monitoring; a status bit can be set for any out-of-limit
condition and detected by polling the device. Alternatively,
SMBALERT interrupts can be generated to flag out-of-limit
conditions to a processor or microcontroller.
8-Bit Limits
The following is a list of 8-bit limits on the ADT7475.
Voltage Limit Registers
Register 0x46, V
Register 0x47, V
Register 0x48, V
Register 0x49, V
Temperature Limit Registers
Register 0x4E, Remote 1 Temperature Low Limit = 0x81 default
Register 0x4F, Remote 1 Temperature High Limit = 0x7F default
Register 0x6A, Remote 1 THERM Temperature Limit = 0x64
default
Register 0x50, Local Temperature Low Limit = 0x81 default
Register 0x51, Local Temperature High Limit = 0x7F default
Register 0x6B, Local THERM Temperature Limit = 0x64 default
Register 0x52, Remote 2 Temperature Low Limit = 0x81 default
Register 0x53, Remote 2 Temperature High Limit = 0x7F
default
Register 0x6C, Remote 2 THERM Temperature Limit = 0x64
default
THERM Limit Register
Register 0x7A, THERM Timer Limit = 0x00 default
16-Bit Limits
The fan TACH measurements are 16-bit results. The fan TACH
limits are also 16 bits, consisting of a high byte and low byte.
Because fans running under speed or stalled are normally the
only conditions of interest, only high limits exist for fan TACHs.
Because the fan TACH period is actually being measured,
exceeding the limit indicates a slow or stalled fan.
Fan Limit Registers
Register 0x54, TACH1 Minimum Low Byte = 0xFF default
Register 0x55, TACH1 Minimum High Byte = 0xFF default
Register 0x56, TACH2 Minimum Low Byte = 0xFF default
CCP
CCP
CC
CC
Low Limit = 0x00 default
High Limit = 0xFF default
Low Limit = 0x00 default
High Limit = 0xFF default
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Register 0x57, TACH2 Minimum High Byte = 0xFF default
Register 0x58, TACH3 Minimum Low Byte = 0xFF default
Register 0x59, TACH3 Minimum High Byte = 0xFF default
Register 0x5A, TACH4 Minimum Low Byte = 0xFF default
Register 0x5B, TACH4 Minimum High Byte = 0xFF default
Out-of-Limit Comparisons
Once all limits have been programmed, the ADT7475 can
be enabled for monitoring. The ADT7475 measures all voltage
and temperature measurements in round-robin format and
sets the appropriate status bit for out-of-limit conditions.
TACH measurements are not part of this round-robin cycle.
Comparisons are done differently, depending on whether
the measured value is being compared to a high or low limit.
Voltage and temperature channels use a window comparator
for error detecting and, therefore, have high and low limits.
Fan speed measurements use only a low limit. This fan limit
is needed only in manual fan control mode.
Analog Monitoring Cycle Time
The analog monitoring cycle begins when a 1 is written to
the start bit (Bit 0) of Configuration Register 1 (0x40).
By default, the ADT7475 powers up with this bit set. The ADC
measures each analog input in turn and, as each measurement
is completed, the result is automatically stored in the appropri-
ate value register. This round-robin monitoring cycle continues
unless disabled by writing a 0 to Bit 0 of Configuration
Register 1.
As the ADC is normally left to free-run in this manner, the time
taken to monitor all the analog inputs is normally not of inter-
est, because the most recently measured value of any input can
be read out at any time.
For applications where the monitoring cycle time is impor-
tant, it can easily be calculated. The total number of channels
measured is
•
•
•
•
High Limit > Comparison Performed
Low Limit ≤ Comparison Performed
One dedicated supply voltage input (V
Supply voltage (V
Local temperature
Two remote temperatures
CC
pin)
CCP
pin)