
SMSC DS – LPC47M14X 
Page 118 
Rev. 03/19/2001 
The state machine will reset after 11 clocks and the process will restart. The process will continue until it is shut off by 
setting the SPEKEY_EN bit (see following sub-section). 
The state machine will reset if there is a period where the clock remains high for more than one keyboard clock 
period (115-145usec) in the middle of the transmission (i.e., before clock 11). This is to prevent the generation of a 
false PME. 
The SPEKEY_EN bit at bit 1 of the CLOCKI32 register at 0xF0 in Logical Device A is used to control the “wake-on-
specific feature.  This bit is used to turn the logic for this feature on and off.  It will disable the 32kHz clock input to the 
logic. The logic will draw no power when disabled.  The bit is defined as follows: 
0= “Wake on specific key” logic is on (default)  
1= “Wake on specific key” logic is off 
Note:
  The generation of a PME for this event is controlled by the PME enable bit (located in the PME_EN1 register 
at bit 5) when the logic for feature is turned on. 
6.17 FAN SPEED CONTROL AND MONITORING 
The LPC47M14x implements fan speed control outputs and fan tachometer inputs.  The implementation of these 
features are described in the sections below. 
6.17.1 
Fan Speed Control 
The fan speed control for the LPC47M14x is implemented as pulse width modulators with fan clock speed selection.  
Pins 54 and 55 are the fan speed control outputs, FAN2 and FAN1, respectively, muxed with GPIOs. These fan 
control pins come up as outputs and are low following a VCC POR and Hard Reset.  These pins may not be used for 
wakeup events under VTR power (VCC=0). 
The configuration registers are defined in the “Runtime Registers” section. 
Fan Speed Control Summary 
The following table illustrates the different modes for the fans. 
Table 57  –  Different Modes for Fan 
FANX CLOCK 
CONTROL 
BIT 
(NOTE 1) 
FANX 
CLOCK 
MULTIPLIER 
BIT 
(NOTE 2) 
FANX 
CLOCK 
SOURCE 
SELECT 
BIT 
(NOTE 3) 
X 
0 
0 
1 
1 
0 
0 
1 
1 
X 
FANX 
CLOCK 
SELECT 
BIT (NOTE 
4) 
F
OUT
6-BIT DUTY 
CYCLE 
CONTROL 
BITS[6:1] 
(DCC) 
DUTY CYCLE 
(%) 
0 
0 
0 
0 
0 
0 
0 
0 
0 
1 
X 
0 
0 
0 
0 
1 
1 
1 
1 
X 
X 
0 
1 
0 
1 
0 
1 
0 
1 
X 
0Hz – LOW 
15.625kHz 
23.438kHz 
40Hz 
60Hz 
31.25kHz 
46.876kHz 
80Hz 
120Hz 
0Hz – HIGH 
0 
- 
1-63 
- 
(DCC/64) 
 100 
- 
Note 1: 
 This is FANx Register Bit 0 
Note 2:
  This is Fan Control Register Bit 2 or 3 
Note 3:
  This is Fan Control Register Bit 0 or 1 
Note 4:
  This is FANx Register Bit 7