Legacy-Free Keyboard/Embedded Controller with SPI and LPC Docking Interface
Chapter 18 Pulse Width Modulators
18.1
Overview
The LPC47N350 has four independent programmable Pulse-Width Modulators (PWM0, PWM1 and
PWM2) that can be used for controlling fan speed. The PWM0, PWM1, and PWM3 have 6-bit pulse-
width resolution, have the ability to force the PWM output always high or low, and they can generate
several fan speeds (F
) as shown in Table 18.1. The PWM2 however, generates fewer fan speeds
OUT
because there is no PWM2 STDBY CLOCK implementation, see Table 18.2.
PWM0, PWM1, and PWM3 can be driven by the system clock when VCC2 is active, or by the
32.768kHz standby clock (RTC) that is available when either VCC2 or VCC1 are active. PWM2 can
only be driven by system clock when VCC2 is active. The PWM2 pin will tri-state when VCC2 = 0v (See
Note 2.2).
PROGRAMMER’S NOTE: The availability of the 32kHz standby clock is subject to the affects of the RTC clock
control bits.
The PWM Speed Control and PWM Control registers are accessible to both the Host and the 8051
through the Mailbox register interface (see Chapter 17, Mailbox Register Interface).
Table 18.1 PWM0, PWM1, and PWM3 Speed Control Summary
FREQUENCY MULTIPLIER BITS
(Note 18.7)
PWMX
CLOCK
MULTI-
PLIER
BIT
00 (1X)
01 (2X)
10 (4X)
11 (8X)
PWMX
STDBY
CLOCK
BIT
PWMX
CLOCK
CONTR
OL BIT
PWMX
CLOCK
SELEC
T 1 BIT
PWMX
CLOCK
SELEC
T 0 BIT
FOUT
FOUT
FOUT
FOUT
6-BIT
DUTY
(KHZ)
(KHZ)
(KHZ)
(KHZ)
CYCLE
CONTR
OL(DCC)
DUTY
CYCLE
(%)
Note 18
.5
Note 18.
1
Note 18.
2
Note 18.
3
Note 18.
4
Note 18
.6
Note 18
.6
Note 18
.6
Note 18
.6
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
1
X
0
0
0
0
1
1
1
1
X
X
0
0
1
1
0
0
1
1
X
X
0
1
0
1
0
1
0
1
X
0 (low)
15.625
23.44
0 (low)
31.25
46.875
0.0814
0.122
62.5
0 (low)
62.5
0 (low)
125
0
(DCC
÷ 64)
× 100
1-63
93.75
0.1628
0.244
125
187.5
0.326
0.488
250
0.407
0.061
31.25
46.875
0.0814
0.122
93.75
0.244
187.5
0.488
375
0.977
0
0
0
0
-
-
-
(high)
(high)
(high)
(high)
1
0
X
X
0 (low)
0 (low)
0 (low)
0 (low)
0
SMSC LPC47N350
199
Revision 1.1 (01-14-03)
DATASHEET
SMSC [ SMSC CORPORATION ]
