
SMSC DS – LPC47M192 
Page 164 
Rev. 03/30/05 
DATASHEET 
NAME 
REG OFFSET 
(hex) 
58 
(R/W) 
DESCRIPTION 
Fan Control 
Default = 0x50 
 on VTR POR 
Fan Control Register 
Bit[0] Fan 1 Clock Source Select 
This bit and the Fan 1 Clock Multiplier bit is used with 
The Fan 1 Clock Select bit in the Fan 1 register (0x56) to 
determine the fan speed F
OUT
.   See Table 56 in “Fan 
Speed Control and Monitoring” section. 
Bit[1] Fan 2 Clock Source Select  
This bit and the Fan 2 Clock Multiplier bit is used with 
The Fan 2 Clock Select bit in the Fan 2 register (0x57) to 
determine the fan speed F
OUT
.   See Table 56 in “Fan 
Speed Control and Monitoring” section. 
Bit[2] Fan 1 Clock multiplier 
0=No multiplier used 
1=Double the fan speed selected by bit 0 of this 
register and bit 7 of the FAN1 register 
Bit[3] Fan 2 Clock multiplier 
0=No multiplier used 
1=Double the fan speed selected by bit 1 of this 
register and bit 7 of the FAN2 register 
Bit[5:4] The FAN1 count divisor.  Clock scalar for 
adjusting the tachometer count.  Default = 2.  
00: divisor = 1 
01: divisor = 2 
10: divisor = 4 
11: divisor = 8 
Bit[7:6] The FAN2 count divisor. Clock scalar for 
adjusting the tachometer count.  Default = 2. 
00: divisor = 1 
01: divisor = 2 
10: divisor = 4 
11: divisor = 8 
Fan Tachometer Register 1 
Bit]7:0] The 8-bit FAN1 tachometer count. The number 
of counts of the internal clock per pulse of the fan.  The 
count value is computed from Equation 1. This value is 
the final (maximum) count of the previous pulse 
(latched). The value in this register may not be valid for 
up to 2 pulses following a write to the preload register. 
Fan Tachometer Register 2 
Bit[7:0] The 8-bit FAN2 tachometer count. The number 
of counts of the internal clock per pulse of the fan.  The 
count value is computed from Equation 1. This value is 
the final (maximum) count of the previous pulse 
(latched). The value in this register may not be valid for 
up to 2 pulses following a write to the preload register. 
Fan Preload Register 1 
Bit[7:0] The FAN1 tachometer preload.  This is the initial 
value used in the computation of the FAN1 count.  
Writing this register resets the tachometer count. 
Fan1 
Register 
Default = 0x00 
 on VTR POR 
Tachometer 
59 
(R) 
Fan2 
Register  
Default = 0x00 
 on VTR POR 
Tachometer 
5A 
(R) 
Fan1 
Register 
Default = 0x00 
 on VTR POR 
Preload 
5B 
(R/W)