EMC2302 Standard Microsystems Corp., EMC2302 Datasheet - Page 29

• Manufacturer Part Number: EMC2302
• Description: Rpm-based Pwm Fan Controller
• Manufacturer: Standard Microsystems Corp.

ADDR
ADDR
Dual RPM-Based PWM Fan Controller
Datasheet
31h
41h
SMSC EMC2302
5.7
30h
40h
5.8
R/W
R/W
R/W
R/W
R/W
R/W
1
0
0
1
1
Bits 3-2 - PWM_BASE2[1:0] - Determines the base frequency of the PWM2 driver.
Bits 1-0 - PWM_BASE1[1:0] - Determines the base frequency of the PWM1 driver.
The Fan Setting register always displays the current setting of the respective fan driver. Reading from
any of the registers 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 is active, the register is read only. Writing to the
register will have no effect and the data will not be stored.
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
The PWM Divide registers determine the final frequency of the respective PWM Fan Driver. Each driver
base frequency is divided by the value of the respective PWM Divide Register to determine the final
Fan Setting Registers
PWM Divide Registers
PWM_BASEX[1:0]
Fan 1 Divide
Fan 2 Divide
REGISTER
Fan 1 Setting
Fan 2 Setting
REGISTER
Drive
Table 5.7 PWM_BASEx[1:0] Bit Decode
Table 5.8 Fan Driver Setting Registers
128
128
=
B7
128
128
Table 5.9 PWM Divide Registers
⎛
⎝
B7
VALUE
-------------------- -
0
0
1
0
1
255
B6
64
64
DATASHEET
B6
64
64
⎞
⎠
×
100%
B5
32
32
29
B5
32
32
Equation
B4
16
16
B4
16
16
[1].
B3
B3
8
8
8
8
BASE FREQUENCY
26.00kHz (default)
B2
19.531kHz
B2
4
4
4
4
4,882Hz
2,441Hz
B1
2
2
B1
2
2
[1]
Revision 1.2 (03-22-10)
B0
1
1
B0
1
1
DEFAULT
DEFAULT
00h
00h
01h
01h