EMC6D103-CK SMSC [SMSC Corporation], EMC6D103-CK Datasheet - Page 44

• Manufacturer Part Number: EMC6D103-CK
• Description: FAN CONTROL DEVICE WITH HIGH FREQUENCY PWM
• Manufacturer: SMSC [SMSC Corporation]

Revision 0.4 (04-04-05)
7.1.4.5
Internal PWM
Window for
Valid Tach
Tach
Pulses
Tach
Pulses
Pulses
Signal
FAN TACHOMETER OPTIONS FOR MODE 2
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Fan Tachometer Reading Registers:
The Tachometer Reading registers are 16 bits, unsigned. When one byte of a 16-bit register is read, the
other byte latches the current value until it is read, in order to ensure a valid reading. The order is LSB first,
MSB second. The value FFFFh indicates that the fan is not spinning, or the tachometer input is not
connected to a valid signal (this could be triggered by a counter overflow). These registers are read
only – a write to these registers has no effect.
Notes:
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2, 3, 5 or 9 “edges” to calculate the fan speed
Guard time A is programmable (8-63 clocks) to account for delays in the system
The PWM frequencies for modes 1 & 2 are: 11.0 Hz, 14.6 Hz, 21.9 Hz, 29.3 Hz, 35.2 Hz, 44.0 Hz,
58.6 Hz, 87.7Hz and 25Khz
Option to ignore first 3 tachometer edges after guard time
Option to force tach reading register to FFFEh to indicate a slow fan.
The Fan Tachometer Reading registers always return an accurate fan tachometer measurement,
even when a fan is disabled or non-functional.
FFFFh indicates that the fan is not spinning, or the tachometer input is not connected to a valid
signal (This could be triggered by a counter overflow).
The Tachometer registers are read only – a write to these registers has no effect.
Mode 1 should be enabled and the tachometer limit register should be set to FFFFh if a tachometer
input is left unconnected.
1
A
Figure 7.5 PWM and Tachometer Concept
B
2
Guard time A
Fan Control Device with High Frequency PWM Support and Hardware Monitoring Features
C
3
DATASHEET
PWM “ON”
44
D
4
(Figure
7.5)
E
5
F
6
SMSC EMC6D103
(Figure
Datasheet
7.5)