Environmental Monitoring and Control Device
limits and parameters for the zone that requires the highest PWM duty cycle, as computed by the Daauttaoshfeaent
algorithm.
When in manual control mode, the Current PWM Duty Registers (30h-32h) become Read/Write. It is then
possible to control the PWM outputs with software by writing to these registers. See Current PWM Duty
Registers description.
When the fan is disabled (100) the corresponding PWM output is driven low (or high, if inverted).
Zone 1: External Diode 1 (processor)
Zone 2: Internal Sensor
Zone 3: External Diode 2
Table 8.6 - Fan Zone Setting
ZON[7:5]
000
FAN CONFIGURATION
Fan on zone 1 auto
001
010
Fan on zone 2 auto
Fan on zone 3 auto
011
Fan always on full
100
101
110
111
Fan disabled
Fan controlled by hottest of zones 2,3
Fan controlled by hottest of zones 1,2,3
Fan manually controlled
8.18.2 BIT [4] PWM INVERT
Bit [4] inverts the PWM output. If set to 1, 100% duty cycle will yield an output that is low for 255 clocks
and high for 1 clock. If set to 0, 100% duty cycle will yield an output that is high for 255 clocks and low for 1
clock.
8.18.3 BIT [3] RESERVED
8.18.4 BITS [2:0] SPIN UP
Bits [2:0] specify the ‘spin up’ time for the fan. When a fan is being started from a stationary state, the
PWM output is held at 100% duty cycle for the time specified in the table below before scaling to a lower
speed. Note: during spin-up, the PWM pin is forced high (OD) for the duration of the spin-up time.
Note: To reduce the spin-up time, the part uses feedback from the tachometers to determine when each
fan has started spinning properly. Spin up for a PWM will end when the tachometer reading register is
below the minimum limit, or the spin-up time expires, whichever comes first. All tachs associated with a
PWM must be below min for spin-up to end. This feature can be disabled by clearing bit 4 of the
Configuration register (7Fh). If disabled, the all fans go on full for the duration of their associated spin up
time. Note that the Tachx minimum registers must be programmed to a value less than FFFFh in order for
the spin up reduction to work properly.
SMSC EMC6D100/EMC6D101
Page 52
Rev. 09-09-04
DATASHEET
SMSC [ SMSC CORPORATION ]
