Environmental Monitoring and Control Device
Datasheet
8.17 Registers 54-5Bh: Fan Tachometer Low Limit
BIT 7
(MSB)
BIT 0
(LSB)
REGISTER
ADDRESS
READ/
WRITE
REGISTER
NAME
DEFAULT
VALUE
BIT 6
BIT 5
BIT 4
BIT 3
BIT 2
BIT 1
Tach1 Minimum
54h
55h
56h
57h
58h
59h
5Ah
5Bh
R/W
R/W
R/W
R/W
R/W
R/W
R/W
R/W
7
15
7
6
14
6
5
13
5
4
12
4
3
11
3
2
10
2
1
9
1
9
1
9
1
9
0
8
0
8
0
8
0
8
FFh
FFh
FFh
FFh
FFh
FFh
FFh
FFh
LSB
Tach1 Minimum
MSB
Tach2 Minimum
LSB
Tach2 Minimum
MSB
15
7
14
6
13
5
12
4
11
3
10
2
Tach3 Minimum
LSB
Tach3 Minimum
MSB
15
7
14
6
13
5
12
4
11
3
10
2
Tach4 Minimum
LSB
Tach4 Minimum
MSB
15
14
13
12
11
10
Setting the Lock bit has no effect on these registers.
The Fan Tachometer Low Limit registers indicate the tachometer reading under which the corresponding
bit will be set in the Interrupt Status Register 2 register. In Auto Fan Control mode, the fan can run at low
speeds, so care should be taken in software to ensure that the limit is low enough not to cause sporadic
alerts.
The fan tachometer will not cause a bit to be set in the interrupt status register if the current value in
Current PWM Duty registers is 00h or if the fan is disabled via the Fan Configuration Register.
Interrupts will never be generated for a fan if its tachometer minimum is set to FFFFh.
8.18 Registers 5C-5Eh: Fan Configuration
BIT 7
BIT 0
(LSB)
REGISTER
ADDRESS
READ/
WRITE
REGISTER
NAME
DEFAULT
VALUE
BIT 6
ZON1
ZON1
ZON1
BIT 5
ZON0
ZON0
ZON0
BIT 4
INV
BIT 3
RES
RES
RES
BIT 2
SPIN2
SPIN2
SPIN2
BIT 1
SPIN1
SPIN1
SPIN1
(MSB)
Fan 1
ZON2
ZON2
ZON2
SPIN0
SPIN0
SPIN0
5Ch
5Dh
5Eh
R/W
R/W
R/W
62h
62h
62h
Configuration
Fan 2
INV
Configuration
Fan 3
INV
Configuration
These registers become read only when the Lock bit is set. Any further attempts to write to these registers
shall have no effect.
8.18.1 BITS [7:5] ZONE/MODE
Bits [7:5] of the Fan Configuration registers associate each fan with a temperature sensor. When in Auto
Fan Mode, the fan will be assigned to a zone, and its PWM duty cycle will be adjusted according to the
temperature of that zone. If ‘Hottest’ option is selected (101 or 110), the fan will be controlled by the hottest
of zones 2 and 3, or of zones 1, 2, and 3. If one of these options is selected, the fan is controlled by the
SMSC EMC6D100/EMC6D101
Page 51
Rev. 09-09-04
DATASHEET
SMSC [ SMSC CORPORATION ]
