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LIMITS, STATUS REGISTERS, AND INTERRUPTS
LIMIT VALUES
Associated with each measurement channel on the ADT7473
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 is detected by polling the device. Alternatively,
SMBALERT interrupts can be generated to flag a processor or
microcontroller of out-of-limit conditions.
8-Bit Limits
The following is a list of 8-bit limits on the ADT7473.
Voltage Limit Registers
Reg. 0x46 V
Low Limit = 0x00 default
CCP
Reg. 0x47 V
High Limit = 0xFF default
CCP
Reg. 0x48 V
Low Limit = 0x00 default
CC
Reg. 0x49 V
High Limit = 0xFF default
CC
Temperature Limit Registers
Reg. 0x4E Remote 1 Temperature Low Limit = 0x01 default
Reg. 0x4F Remote 1 Temperature High Limit = 0xFF default
Reg. 0x6A Remote 1 THERM Limit = 0xA4 default
Reg. 0x50 Local Temperature Low Limit = 0x01 default
Reg. 0x51 Local Temperature High Limit = 0xFF default
Reg. 0x6B Local THERM Limit = 0xA4 default
Reg. 0x52 Remote 2 Temperature Low Limit = 0x01 default
Reg. 0x53 Remote 2 Temperature High Limit = 0xFF default
Reg. 0x6C Remote 2 THERM Limit = 0xA4 default
THERM Limit Register
Reg. 0x7A THERM 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
Reg. 0x54 TACH1 Minimum Low Byte = 0xFF default
Reg. 0x55 TACH1 Minimum High Byte = 0xFF default
Reg. 0x56 TACH2 Minimum Low Byte = 0xFF default
Reg. 0x57 TACH2 Minimum High Byte = 0xFF default
Reg. 0x58 TACH3 Minimum Low Byte = 0xFF default
Reg. 0x59 TACH3 Minimum High Byte = 0xFF default
Reg. 0x5A TACH4 Minimum Low Byte = 0xFF default
Reg. 0x5B TACH4 Minimum High Byte = 0xFF default
Out-of-Limit Comparisons
Once all limits have been programmed, the ADT7473 can be
enabled for monitoring. The ADT7473 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. Compari-
sons are done differently depending on whether the measured
value is being compared to a high or low limit.
High Limit: > Comparison Performed
Low Limit: ≤ Comparison Performed
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 (Reg. 0x40). By
default, the ADT7473 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 appropriate
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
interest, because the most recently measured value of any input
can be read out at any time.
For applications where the monitoring cycle time is important,
it can easily be calculated. The total number of channels
measured is
•
One dedicated supply voltage input (V
•
Supply voltage (V
•
Local temperature
•
Two remote temperatures
Rev. 0 | Page 19 of 76
)
CCP
pin)
CC
ADT7473
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