EMC2301 Standard Microsystems Corp., EMC2301 Datasheet - Page 29

• Manufacturer Part Number: EMC2301
• Description: Rpm-based Pwm Fan Controller
• Manufacturer: Standard Microsystems Corp.

ADDR
ADDR
32h
RPM-Based PWM Fan Controller
Datasheet
31h
SMSC EMC2301
5.8
5.9
R/W
R/W
R/W
R/W
The PWM Divide registers determine the final frequency of the PWM Fan Driver. The driver base
frequency is divided by the value of the 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.
The Fan Configuration 1 register controls the general operation of the RPM-based Fan Speed Control
Algorithm used for the Fan Driver.
Bit 7 - EN_ALGO - enables the RPM-based Fan Speed Control Algorithm.
Bits 6- 5 - RANGE[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
Bits 4-3 - EDGES[1:0] - determines the minimum number of edges that must be detected on the
TACHx signal to determine a single rotation. A typical fan measured 5 edges (for a 2-pole fan). For
more accurate tachometer measurement, the minimum number of edges measured may be increased.
Increasing the number of edges measured with respect to the number of poles of the fan will cause
the TACH Reading registers to indicate a fan speed that is higher or lower than the actual speed. In
PWM Divide Register
Fan Configuration 1 Register
1
0
0
1
1
‘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.
Configuration 1
REGISTER
Fan Divide
REGISTER
RANGE[1:0]
Fan
Table 5.10 Fan Configuration 1 Register
128
B7
ALGO
EN_
B7
Table 5.9 PWM Divide Register
Table 5.11 Range Decode
0
0
1
0
1
B6
64
DATASHEET
RANGE[1:0]
B6
Table
B5
32
29
B5
5.11.
B4
16
REPORTED MINIMUM
EDGES[1:0]
B4
1000 (default)
B3
8
RPM
2000
4000
500
B3
B2
4
B2
UPDATE[2:0]
B1
2
B1
Revision 1.2 (03-22-10)
TACH COUNT
MULTIPLIER
B0
1
B0
1
2
4
8
DEFAULT
DEFAULT
01h
2Bh