emc2105 Standard Microsystems Corp., emc2105 Datasheet - Page 66

• Manufacturer Part Number: emc2105
• Description: Emc2105 Rpm-based High Side Fan Controller With Hardware Thermal Shutdown
• Manufacturer: Standard Microsystems Corp.

ADDR
50h
Revision 1.74 (05-08-08)
6.28
6.29
ADDR
4Eh
4Fh
R/W
R/W
RPM
Configuration
R/W
The TACH Reading Registers’ contents describe the current tachometer reading for each of 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.
Whenever the high byte register is read, the corresponding low byte data will be loaded to internal
shadow registers so that when the low byte is read, the data will always coincide with the previously
read high byte.
REGISTER
The Look Up Table Configuration Register holds the setup information for the two temperature to fan
drive look up tables.
Bit 7 - USE_DTS_F1 - This bit determines whether the Pushed Temperature 1 registers are using
DTS data.
TACH Reading Registers
Look Up Table Configuration Register
R
R
shows the simplified translation of TACH Reading Register count to RPM assuming a 2-pole fan,
LUT
=
------------------- -
(
poles
RPM
1
REGISTER
Fan TACH
Fan TACH
Low Byte
shows the detailed conversion from TACH measurement (COUNT) to RPM while
)
×
=
USE_D
TS_F1
--------------------------------- -
COUNT
3,932,160 m
------------------------------------- -
Table 6.43 Look Up Table Configuration Register
B7
(
COUNT
n 1
–
Table 6.42 TACH Reading Registers
4096
)
×
B7
16
USE_D
TS_F2
---- -
m
1
×
B6
×
f
TACH
2048
B6
DATASHEET
8
LUT_L
×
RPM-Based High Side Fan Controller with Hardware Thermal Shutdown
OCK
B5
60
1024
B5
66
4
TACH /
DRIVE
512
B4
B4
2
poles = number of poles of the fan
COUNT = TACH Reading Register
measurement frequency (typically
256
m = the multiplier defined by the
B3
n = number of edges measured
1
(typically 5 for a 2 pole fan)
TEMP3_CFG
B3
f
TACH
[1:0]
value (in decimal)
128
B2
-
RANGe bits
(typically 2)
32.768kHz)
= the tachometer
B2
where:
B1
64
-
TEMP4_CFG
B1
B0
32
-
[1:0]
SMSC EMC2105
DEFAULT
B0
Datasheet
FFh
F8h
Equation
[3]
[4]
DEFAULT
00h