EMC2302 Standard Microsystems Corp., EMC2302 Datasheet - Page 36

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

ADDR
38h
48h
Revision 1.2 (03-22-10)
5.14
5.15
ADDR
39h
49h
R/W
R/W
R/W
R/W
R/W
R/W
The Fan Minimum Drive registers store the minimum drive setting for each RPM-based Fan Speed
Control Algorithm. The RPM-based Fan Speed Control Algorithm will not drive the fan at a level lower
than the minimum drive unless the target Fan Speed is set at FFh (see
During normal operation, if the fan stops for any reason (including low drive), the RPM-based Fan
Speed Control Algorithm will attempt to restart the fan. Setting the Fan Minimum Drive Register to a
setting that will maintain fan operation is a useful way to avoid potential fan oscillations as the control
circuitry attempts to drive it at a level that cannot support fan operation.
The Fan Minimum Drive Registers are software locked.
The Valid TACH Count registers store the maximum TACH Reading Register value to indicate that
each fan is spinning properly. The value is referenced at the end of the Spin Up Routine to determine
if the fan has started operating and decide if the device needs to retry. See
for translating the count to an RPM.
If the TACH Reading Register value exceeds the Valid TACH Count Register (indicating that the Fan
RPM is below the threshold set by this count), then a stalled fan is detected. In this condition, the
algorithm will automatically begin its Spin Up Routine.
If a TACH Target setting is set above the Valid TACH Count setting, then that setting will be ignored
and the algorithm will use the current fan drive setting.
The Valid TACH Count registers are software locked.
Fan Minimum Drive Registers
Valid TACH Count Registers
REGISTER
Minimum
Minimum
Valid TACH
Valid TACH
REGISTER
Fan 1
Fan 2
Drive
Drive
Count 1
Count 2
128
128
4096
4096
Table 5.24 Minimum Fan Drive Registers
B7
B7
Table 5.25 Valid TACH Count Registers
2048
2048
B6
B6
64
64
DATASHEET
1024
1024
B5
B5
32
32
36
512
512
B4
B4
16
16
256
256
B3
B3
8
8
128
128
B2
B2
Dual RPM-Based PWM Fan Controller
4
4
Section
B1
64
64
Equation [2]
B1
2
2
5.17).
B0
32
32
B0
SMSC EMC2302
1
1
in
DEFAULT
Section 5.18
Datasheet
F5h
F5h
DEFAULT
(40%)
(40%)
66h
66h