EMC2103 Standard Microsystems Corporation, EMC2103 Datasheet - Page 62

• Manufacturer Part Number: EMC2103
• Description: Rpm-based Fan Controller with HW Thermal Shutdown
• Manufacturer: Standard Microsystems Corporation

Revision 0.85 (01-29-08)
6.30
6.31
ADDR
ADDR
4Ch
4Dh
4Eh
4Fh
R/W
R/W
R/W
R/W
The TACH Target Register holds the target tachometer value that is maintained by the RPM based
Fan Speed Control Algorithm.
The value in the TACH Target Register will always reflect the current TACH Target value. If the Look
Up Table is active and configured to operate in RPM Mode, then this register will be read only. Writing
to this register will have no affect and the data will not be stored.
If the algorithm is enabled then setting the TACH Target Register to FFh will disable the fan driver (set
the PWM duty cycle to 0%). Setting the TACH Target to any other value (from a setting of FFh) will
cause the algorithm to invoke the Spin Up Routine after which it will function normally.
The TACH Reading Register contents describe the current tachometer reading for the fan. By default,
the data represents the fan speed as the number of 32kHz clock periods that occur for a single
revolution of the fan.
Equation [3]
[4]
measuring 5 edges, with a frequency of 32.768kHz.
See
TACH Target Register
TACH Reading Register
R
R
shows the simplified translation of TACH Reading Register count to RPM assuming a 2-pole fan,
Appendix B
TACH Target
REGISTER
REGISTER
Target Low
Fan TACH
Fan TACH
Fan TACH
Low Byte
shows the detailed conversion from TACH measurement (COUNT) to RPM while
Byte
for a table enumerating the RPM to TACH conversion for the default settings.
Table 6.47 TACH Reading Register
4096
4096
Table 6.46 TACH Target Register
B7
B7
16
16
2048
2048
B6
B6
DATASHEET
8
8
1024
1024
B5
B5
62
4
4
512
512
B4
B4
2
2
RPM-Based Fan Controller with HW Thermal Shutdown
256
256
B3
B3
1
1
128
128
B2
B2
-
-
B1
B1
64
64
-
-
B0
B0
32
32
-
-
SMSC EMC2103
DEFAULT
DEFAULT
Datasheet
F8h
FFh
FFh
F8h
Equation