SCH3112I-NE SMSC [SMSC Corporation], SCH3112I-NE Datasheet - Page 259

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

LPC IO with 8042 KBC, Reset Generation, HWM and Multiple Serial Ports
Datasheet
APPLICATION NOTE: This bit should always be enabled (set) to prevent fan tachometer interrupts during spinup.
SMSC SCH311X
ZON[7:5]
000
001
010
011
100
101
110
111
■
■
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.
Bit [3] Forced Spin-up Enable
Bit [3] enables the forced spin up option for a particular PWM. If set to 1, the forced spin-up feature
is enabled for the associated PWM. If set to 0, the forced spin-up feature is disabled for the associated
PWM.
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 for the duration of the spin-up time (i.e.,
100% duty cycle = 256/256)
Note: To reduce the spin-up time, this device has implemented a feature referred to as Spin Up
Zone 2 is controlled by the Ambient Reading Register.
Zone 3 is controlled by Remote Diode 2 Temp Reading register
Reduction. Spin Up Reduction 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 prematurely. This feature can
be disabled by clearing bit 4 (SUREN) 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.
Fan on zone 1 auto
Fan on zone 2 auto
Fan on zone 3 auto
Fan always on full
Fan disabled
Fan controlled by hottest of zones 2,3
Fan controlled by hottest of zones 1,2,3
Fan manually controlled
Table 24.7 Fan Zone Setting
DATASHEET
243
PWM CONFIGURATION
Rev 0.2 (09-28-04)