Environmental Monitoring and Control Device
Datasheet
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
PWM Duty
31h
32h
R/W1
R/W1
Fan2 Current
7
7
6
6
5
5
4
4
3
3
2
2
1
1
0
0
N/A
N/A
PWM Duty
Fan3 Current
PWM Duty
Note 1: these registers are only writeable when the associated fan is in manual mode. These registers
become read only when the Lock bit is set. Any further attempts to write to these registers shall have no
effect.
The Current PWM Duty registers store the duty cycle that the EMC6D100/EMC6D101 Chip is currently
driving the PWM signals at. At initial power-on, the duty cycle is 100% and thus, when read, this register
will return FFh. After the Ready/Lock/Start Register Start bit is set, this register and the PWM signals are
updated based on the algorithm described in the Auto Fan Control Operating Mode section, unless the
associated fan is in manual mode – see below.
When read, the Current PWM Duty registers return the current PWM duty cycle for the respective PWM
signal.
These registers are read only – a write to these registers has no effect.
Note: If the current PWM duty cycle registers are written while the part is not in manual mode and the start
bit is zero, data will be stored in a hidden registers that will only be active and observable when the start bit
is set. While the part is not in manual mode and the start bit is zero, the current PWM duty cycle registers
will read back FFh.
8.7.1 MANUAL MODE
In manual mode, the current duty cycle registers are writeable to control the PWMs. In manual mode,
when the start bit is set to 1, the current duty cycle registers are writeable to control the PWMs. Also in
manual mode, when the lock bit is set to 1, the current duty cycle registers are Read-Only.
The PWM duty cycle is represented as follows:
Table 8.3 - PWM Duty vs. Register Reading
CURRENT DUTY
VALUE (DECIMAL)
VALUE (HEX)
00h
0%
0
25%
50%
64
40h
80h
FFh
128
255
100%
During spin-up, the PWM duty cycle is reported as 0%.
SMSC EMC6D100/EMC6D101
Page 43
Rev. 09-09-04
DATASHEET
SMSC [ SMSC CORPORATION ]
