Fan Control Device with High Frequency PWM and Temperature Monitors
Datasheet
Chapter 7 Fan Control
The following sections describe the various fan control and monitoring modes in the part.
7.1
General Description
This Fan Control device is capable of driving multiple DC fans via three PWM outputs and monitoring
up to four 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 four pins dedicated to monitoring the operation of each fan are the TACH[1:4]
pins. Fans equipped with Fan Tachometer outputs may be connected to these pins to monitor the
speed of the fan.
7.1.1
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:
Registers 54h – 5Bh: TACHx Minimum
Registers 5Fh – 61h: Zone x Range/FANx Frequency
Registers 5Ch – 5Eh: PWMx Configuration
Registers 62h − 63h: 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
Register 81h: TACH_PWM Association
Registers 90h – 93h: Tachx Option Registers
Registers 94h – 96h: PWMx Option Registers
The limit and configuration registers are defined in Chapter 8, Register Set.
Notes:
The START bit in Register 40h Ready/Lock/Start Register must be set to ‘1’ to start temperature
monitoring functions.
Setting the PWM Configuration register to Auto Mode will not take effect until after the START bit
is set
7.1.2
Device Set-Up
BIOS will follow the steps listed below to configure the fan registers on this device. The registers
corresponding to each function are listed. All steps may not be necessary if default values are
acceptable. Regardless of all changes made by the BIOS to the limit and parameter registers during
configuration, the EMC2300 will continue to operate based on default values until the Start bit, in the
Ready/Lock/Start register, is set. Once the Start bit is set, the EMC2300 will operate according to the
values that were set by BIOS in the limit and parameter registers.
1. Set limits and parameters (not necessarily in this order)
2. [5F-61h] Set PWM frequencies and Auto Fan Control Range.
3. [62-63h] Set Ramp Rate Control
SMSC EMC2300
Revision 0.2 (06-14-06)
DATA2S9HEET
SMSC [ SMSC CORPORATION ]
