ADM1033
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16
The construction of a filter allows the ADM1033 and the
remote temperature sensor to operate in noisy environments.
Figure 29 shows a low-pass R-C-R filter with the following
values: R = 100 W and C = 1 nF. This filtering reduces both
common-mode noise and differential noise.
Figure 29. Filter between Remote Sensor
and ADM1033
100 W
100 W
1 nF
D+
D−
REMOTE
TEMPERATURE
SENSOR
Limits, Status Registers, and Interrupts
High and low limits are associated with each measurement
channel on the ADM1033. 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,
SMBusALERT
s can be generated to flag a processor or
microcontroller of an out-of-limit condition.
8-bit Limits
The following is a list of all the 8-bit limits on the
ADM1033:
Table 15. TEMPERATURE LIMIT REGISTERS
Register Description Default
0x0B Local High Limit 0x8B (75C)
0x0C Local Low Limit 0x54 (20C)
0x0D Local THERM Limit 0x95 (85C)
0x0E Remote 1 High Limit 0x8B (75C)
0x0F Remote 1 Low Limit 0x54 (20C)
0x10 Remote 1 THERM Limit 0x95 (85C)
Table 16. THERM LIMIT REGISTERS
Register Description Default
0x19 THERM % Limit 0xFF default
Out-of-Limit Comparisons
The ADM1033 measures all parameters in a round-robin
format and sets the appropriate status bit for out-of-limit
conditions. Comparisons are made differently, depending
on whether the measured value is compared to a high or low
limit.
High Limit: Comparison Performed
Low Limit: < Comparison Performed
Analog Monitoring Cycle Time
The analog monitoring cycle time begins on powerup, or,
if monitoring has been disabled, by writing a 1 to the monitor/
STBY bit of Configuration Register 1, (Address 0x01). The
ADC measures each one of the analog inputs in turn; as each
measurement is completed, the result is automatically stored
in the appropriate value register. The round-robin monitoring
cycle continues unless it is disabled by writing a 0 to the
monitor/STBY bit (Bit 0) of Configuration Register 1
(Address 0x01).
The ADC performs round-robin conversions and takes
11 ms for the local temperature measurement and 32 ms for
each remote temperature measurement with averaging
enabled.
The total monitoring cycle time for the average
temperatures is therefore nominally.
32 ) 11 + 43 ms
(eq. 2)
Once the conversion time elapses, the round robin starts
again. For more information, refer to the Conversion Rate
Register section.
Fan TACH measurements take place in parallel and are not
synchronized with the temperature measurements in any way.
Status Registers
The results of limit comparisons are stored in the status
registers. A 1 represents an out-of-limit measurement; a 0
represents an in-limit measurement. The status registers are
located at Addresses 0x4F to 0x51.
If the measurement is outside its limits, the corresponding
status register bit is set to 1. It remains set at 1 until the
measurement falls back within its limits and it is read or until
an ARA is completed.
Poll the state of the various measurements by reading the
status registers over the serial bus. If Bit 0 (ALERT
low) of
Status Register 3 (Address 0x51) is set, this means that the
ALERT
output has been pulled low by the ADM1033.
Pin 14 can be configured as a SMBusALERT
output. This
automatically notifies the system supervisor of an
out-of-limit condition. Reading the status register clears the
status bit as long as the error condition is gone.
Status register bits are sticky. Whenever a status bit is set
due to an out-of-limit condition, it remains set even after the
triggering event has gone. The only way to clear the status
bit is to read the status register (after the event has gone).
Interrupt mask registers (Reg. 0x08, Reg. 0x09, Reg. 0x0A)
allow individual interrupt sources to be masked from
causing an ALERT
. However, if one of these masked
interrupt sources goes out of limit, its associated status bit is
set in the status register.
