emc2101 Standard Microsystems Corp., emc2101 Datasheet - Page 39

• Manufacturer Part Number: emc2101
• Description: Emc2101 Fan Control With 1?c Accurate Temperature Monitoring
• Manufacturer: Standard Microsystems Corp.

ADDR
46h
47h
ADDR
48h
49h
SMBus Fan Control with 1°C Accurate Temperature Monitoring
Datasheet
SMSC EMC2101
6.14
6.15
R/W
R
R
ENABLE
R/W
R/W
R/W
0
0
0
0
0
1
TACH Reading
TACH Reading
REGISTER
High Byte
Low Byte
The TACH Registers hold the 16-bit TACH Reading. This reading represents the number of TACH
counts detected. The RPM of the fan can be determined by Equation
bit weighting of each TACH[15:0] bit is shown in parenthesis after the value. When determining the
final fan speed, the TACH[15:0] bits need to be decoded into an equivalent decimal number.
The TACH Limit Registers store the maximum TACH count that the fan is expected to operate at.
TACH count is inversely proportional to the actual fan speed. This limit is used to guarantee that the
fan has spun up properly. If the measured TACH is higher than this limit (indicating that the fan speed
is lower than the minimum RPM value), then the TACH bit is set in the Status Register.
Additionally if the measured TACH count exceeds this limit, depending on the status of the
TACH_M[1:0] bits (see
TACH Reading Registers
TACH Limit Registers
REGISTER
TACH Limit
TACH Limit
High Byte
Low Byte
RPM
=
------------------------------------------- -
TACH _ COUNT
TACH15
(32768)
TACH7
(128)
TACH_
TACH_
B7
5 400 000
B2
L15
,
B7
X
L7
0
1
1
1
1
Table 6.17 TACH Reading Low Byte Register
Table 6.15 CPU Beta Values (continued)
,
Section
Table 6.16 TACH Reading Registers
TACH14
(16384)
TACH6
TACH_
TACH_
(64)
B6
L14
B6
L6
6.16), the TACH reading registers may be forced to FFFFh.
DATASHEET
TACH13
TACH5
TACH_
TACH_
(8192)
(32)
L13
B5
B5
L5
B1
X
1
0
0
1
1
39
TACH_
TACH_
TACH12
TACH4
(4096)
L12
B4
L4
(16)
B4
Where: TACH_COUNT is the
decimal representation of the
TACH_
TACH_
L11
TACH11
B3
L3
TACH3
(2048)
B3
(8)
TACH[13:0] bits.
B0
X
1
0
1
0
1
TACH_
TACH_
L10
B2
L2
TACH10
TACH2
(1024)
B2
(4)
[3]
(see also
TACH_
TACH_
0.33
0.43
1.00
2.33
Disabled
Automatic detection
B1
L1
L9
TACH1
TACH9
(512)
MINIMUM BETA
Revision 2.53 (02-19-08)
B1
(2)
TACH_
TACH_
Appendix
B0
L0
L8
TACH0
TACH8
(256)
B0
(1)
[3]
DEFAULT
B). The
FFh
FFh
DEFAULT
FFh
FFh