Environmental Monitoring and Control Device
Datasheet
When in manual mode, the current PWM duty cycle registers can be written to adjust the speed of the
fans, when the start bit is set. These registers are not writeable when the lock bit is set.
7.4.2 AUTO FAN CONTROL OPERATING MODE
The EMC6D100/EMC6D101 chip implements automatic fan control. In Auto Fan Mode, the chip
automatically adjusts the PWM duty cycle of the PWM outputs, according to the flow chart below. PWM
outputs are assigned to a thermal zone based on the fan configuration registers. It is possible to have
more than one PWM output assigned to a thermal zone. For example, PWM outputs 2 and 3, connected to
two chassis fans, may both be controlled by thermal zone 2. At any time, if the temperature of a zone
exceeds its absolute limit, all PWM outputs go to 100% duty cycle to provide maximum cooling to the
system (except those fans that are disabled).
It is possible to have a single fan controlled by multiple zones, turning on when either zone requires
cooling based on its individual settings.
A VCC POR resets all values to their initial or default states. If the device is not in reset and the start bit is
set to ‘1’ the configuration and parameter registers become read only when the start bit is set and are not
latched inside of the auto fan block.
If the start bit is one the Auto Fan Control block will evaluate the temperature in the zones configured for
each Fan in a round robin method. The Auto Fan Control block completely evaluates the zones for all
three fans in a maximum of 0.25sec.
SMSC EMC6D100/EMC6D101
Page 31
Rev. 09-09-04
DATASHEET
SMSC [ SMSC CORPORATION ]
