EMC2303 Datasheet, PDF (33/51 Pages) SMSC Corporation – Multiple RPM-Based PWM Fan Controller

Multiple RPM-Based PWM Fan Controller
Datasheet
5.8
PWM Divide Registers
Table 5.9 PWM Divide Registers
ADDR R/W
REGISTER
B7
B6
B5
B4
B3
B2
B1
B0 DEFAULT
31h
R/W Fan 1 Divide 128 64
32
16
8
4
2
1
01h
41h
R/W Fan 2 Divide 128 64
32
16
8
4
2
1
01h
51h
R/W Fan 3 Divide 128 64
32
16
8
4
2
1
01h
5.9
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
frequency. The duty cycle settings are not affected by these settings, only the final frequency of the
PWM driver. A value of 00h will be decoded as 01h.
Fan Configuration 1 Registers
ADDR
32h
42h
52h
Table 5.10 Fan Configuration 1 Registers
R/W
REGISTER
B7
B6 B5 B4 B3 B2 B1 B0 DEFAULT
R/W
Fan 1
Configuration 1
EN_
ALGO1
RANGE1[1:0] EDGES1[1:0]
UPDATE1[2:0]
2Bh
R/W
Fan 2
Configuration 1
EN_
ALGO2
RANGE2[1:0] EDGES2[1:0]
UPDATE2[2:0]
2Bh
R/W
Fan 3
Configuration 1
EN_
ALGO3
RANGE3[1:0] EDGES3[1:0]
UPDATE3[2:0]
2Bh
The Fan Configuration 1 registers control the general operation of the RPM-based Fan Speed Control
Algorithm used for the respective Fan Driver.
Bit 7 - EN_ALGOx - enables the RPM-based Fan Speed Control Algorithm.
„ ‘0’ - (default) the control circuitry is disabled and the fan driver output is determined by the Fan
Driver Setting Register.
„ ‘1’ - the control circuitry is enabled and the Fan Driver output will be automatically updated to
maintain the programmed fan speed as indicated by the TACH Target Register.
Bits 6- 5 - RANGEx[1:0] - Adjusts the range of reported and programmed tachometer reading values.
The RANGE bits determine the weighting of all TACH values (including the Valid TACH Count, TACH
Target, and TACH reading) as shown in Table 5.11.
Table 5.11 Range Decode
RANGEX[1:0]
1
0
0
0
0
1
REPORTED MINIMUM
RPM
500
1000 (default)
TACH COUNT
MULTIPLIER
1
2
SMSC EMC2303
33
DATASHEET
Revision 1.1 (10-12-09)