SCH3112I-NE SMSC [SMSC Corporation], SCH3112I-NE Datasheet - Page 214

• 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)
23.11.4
23.12
23.13
23.13.1
Offset Registers
There are three offset registers:
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Offset Register 1 is used for Remote Diode 1 Temp Reading. Offset Register 2 is used for Remote
Diode 2 Temp Reading. Offset Register Ambient is used for internal Temp Reading.
The Offset Registers contain a 2's complement value which is added (or subtracted if the number is
negative) to the corresponding temperature reading. The default value in the offset register is zero, so
initially zero is always added to the temperature reading.
Each temperature measurement input is assigned to a Thermal Zone to control the PWM outputs in
Auto Fan Control mode. These zone assignments are as follows:
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The auto fan control logic uses the zone temperature reading to control the duty cycle of the PWM
outputs.
The following sections describe the various fan control and monitoring modes in the part.
This Fan Control device is capable of driving multiple DC fans via three PWM outputs and monitoring
up to three fans equipped with tachometer outputs in either Manual Fan Control mode or in Auto Fan
Control mode. The three fan control outputs (PWMx pins) are controlled by a Pulse Width Modulation
(PWM) scheme. The three pins dedicated to monitoring the operation of each fan are the
FANTACH[1:3] pins. Fans equipped with Fan Tachometer outputs may be connected to these pins to
monitor the speed of the fan.
Limit and Configuration Registers
At power up, all the registers are reset to their default values and PWM[1:3] are set to “Fan always on
Full” mode. Before initiating the monitoring cycle for either manual or auto mode, the values in the limit
and configuration registers should be set.
The limit and configuration registers are:
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Thermal Zones
Fan Control
Offset Register Ambient (1Dh)
Offset Register 2 (1Eh)
Offset Register 1 (1Fh)
Zone 1 = Remote Diode 1 (Processor)
Zone 2 = Ambient Temperature Sensor
Zone 3 = Remote Diode 2
Registers 54h – 5Bh: TACHx Minimum
Registers 5Fh – 61h: Zone x Range/FANx Frequency
Registers 5Ch – 5Eh: PWMx Configuration
Registers 62h − 63h: Min/Off, PWM x Ramp Rate Control
Registers 64h – 66h: PWMx Minimum Duty Cycle
Registers 67h – 69h: Zone x Low Temp LIMIT
Registers 6Ah – 6Ch: Zone x Temp Absolute Limit – all fans in Auto Mode are set to full
Registers 6Dh – 6Eh: Zone x Hysteresis
Register 81h: TACH_PWM Association
DATASHEET
LPC IO with 8042 KBC, Reset Generation, HWM and Multiple Serial Ports
198
SMSC SCH311X
Datasheet