Dual RPM-Based PWM Fan Controller with Hardware Thermal Shutdown
Datasheet
APPLICATION NOTE: If any of the External Diode 1, External Diode 2, External Diode 3 is configured to operate
as a voltage input, then the corresponding temperature high and low limit registers are
compared against the measured voltage. The data format is the same as the measured
voltage and these registers should be updated accordingly.
Additionally, the EMC2104 contains low limits for all temperature channels. If the temperature channel
drops below the low limit, then the appropriate status bit is set and the ALERT# pin are asserted (if
enabled).
All Limit Registers are Software Locked.
6.20
Fan Setting Registers
Table 6.26 Fan Driver Setting Register
ADDR
R/W
REGISTER
B7
B6
B5
B4
B3
B2
B1
B0
DEFAULT
40h
80h
R/W
R/W
Fan 1 Setting
Fan 2 Setting
128
128
64
64
32
32
16
16
8
8
4
4
2
2
1
1
00h
00h
The Fan 1 Setting Register always displays the current setting of the Fan 1 Driver.Likewise, the Fan
2 Setting Register always displays the current setting of the Fan 2 driver. Reading from either register
will report the current fan speed setting of the appropriate fan driver regardless of the operating mode.
Therefore it is possible that reading from this register will not report data that was previously written
into this register.
While the RPM based Fan Speed Control Algorithm or the Look Up Table are active (or both), then
the register is read only. Writing to the register will have no affect and the data will not be stored.
If both the RPM based Fan Control Algorithm and the Look Up Table are disabled, then the register
will be set with the previous value that was used. The register is read / write and writing to this register
will affect the fan speed.
If the Fan 2 fan driver is disabled and the DAC2 / PWM2 / GPIO2 and TACH2 / GPIO1 pins are used
as GPIOs, then the Fan 2 Setting Register will read 00h.
The contents of the register represent the weighting of each bit in determining the final output voltage.
The output drive for a PWM output is given by Equation [2].
VALUE
⎛
⎝
⎞
--------------------
Drive =
× 100%
⎠
255
[2]
6.21
PWM 1 and 2 Divide Registers
Table 6.27 PWM 1 and 2 Divide Registers
ADDR
R/W
REGISTER
B7
B6
B5
B4
B3
B2
B1
B0
DEFAULT
41h
81h
R/W
R/W
PWM 1 Divide
PWM 2 Divide
128
128
64
64
32
32
16
16
8
8
4
4
2
2
1
1
01h
01h
Revision 1.74 (05-08-08)
SMSC EMC2104
DATA6S4HEET
SMSC [ SMSC CORPORATION ]
