SCH3112I-NE SMSC [SMSC Corporation], SCH3112I-NE Datasheet - Page 230

• Manufacturer Part Number: SCH3112I-NE
• Description: LPC IO with 8042 KBC, Reset Generation, HWM and Multiple Serial Ports
• Manufacturer: SMSC [SMSC Corporation]

Rev 0.2 (09-28-04)
23.13.5.1
Adjusting Minimum Temperature Based on Top Temperature
This describes the option for adjusting the minimum temperature based on the Top Temperature.
The AMTA option automatically adjusts the preprogrammed value for the minimum temperature and
shifts the temperature range for the autofan algorithm to better suit the environment of the system, that
is, to bias the operating range of the autofan algorithm toward the low end of the temperature range.
It uses a programmed value for the “Top temperature” for the zone to shift the temperature range of
the autofan algorithm, and therefore the speed of the fan, toward the middle of the fan control function
(PWM Duty Cycle vs. Temperature). This feature will effectively prevent the fans from going on full,
thereby limiting the noise produced by the fans.
The value of the Top temperature for each zone can be programmed to be near the center of the
temperature range for the zone, or near the maximum as defined by the low temp limit plus range.
The implementation of the AMTA feature is defined as follows:
This feature can be individually enabled to operate for each zone. Each zone has a separate enable
bit for this feature (register 0B7h). Note that if the piecewise linear fan function is used, the minimum
temperature for the zone (Zone x Low Temp Limit register) is shifted down, which will result in each
segment being shifted down.
This feature adjusts the minimum temperature for each zone for the autofan algorithm based on the
current temperature reading for the zone exceeding the Top temperature.
When the current temperature for the zone exceeds the Top temperature for the zone, the minimum
temperature value is reloaded with the value of the minimum temperature limit minus a programmable
temperature adjustment value for the zone, as programmed in the Min Temp Adjust registers. The
temperature adjustment value is programmable for each zone.
The zone must exceed the limits set in the associated Top Temp Zone [3:1] register for two
successive monitoring cycles in order for the minimum temperature value to be adjusted (and
for the associated status bit to be set).
The new minimum temperature value is loaded into the low temp limit register for each zone (Zone x
Low Temp Limit). This will cause the temperature range of the autofan algorithm to be biased down in
temperature.
Note: When the minimum temperature for the zone is adjusted, the autofan algorithm will operate
This process will repeat after a delay until the current temperature for the zone no longer exceeds the
Top temperature for the zone.
Once the minimum temp value is adjusted, it will not adjust again until after a programmable time delay.
The delay is programmed for each zone in the Min Temp Adjust Delay registers. The adjust times are
as follows: 1, 2, 3, and 4 minutes.
Figure 8.5 illustrates the operation of the AMTA for one adjustment down in minimum temperature
resulting from the temperature exceeding the Top temperature. The effect on the linear fan control
function (PWM Duty Cycle vs. Temperature) is shown.
with a new fan control function (PWM Duty Cycle vs. Temperature), which will result in a new
PWM duty cycle value. The PWM will move to the new value smoothly, so there is little audible
effect when the PWM Ramp rate control is enabled.
DATASHEET
LPC IO with 8042 KBC, Reset Generation, HWM and Multiple Serial Ports
214
SMSC SCH311X
Datasheet