abstract.txt

LPC932用CCU实现PWM

LPC932 EXAMPLE:	CREATING PWM SIGNALS USING THE CAPTURE COMPARE UNIT (CCU)
by Christian Kulig, Philips Semiconductor, 12/06/02


INTRODUCTION:
The LPC932 can be used to create Pulse Width Modulated PWM signals. 
With a PWM signal and a simple RC-filter it is possible to generate an 
analog output signal. The current analog value of this signal at a certain 
point in time is proportional to its Duty Cycle which is percentage of  
High Time during one period or the average value during a particular 
period. That means after low pass filtering, (e.g. RC circuit) the signal 
becomes analog, with an actual value controlled by the microcontroller. 
The PWM functionality enables the LPC932 to control for example the speed 
of DC motors or the brightness of electric lighting.


DESCRIPTION:
The LPC932 has various ways to create many types of PWM signals.
This sample utilizes the Capture Compare Unit (CCU) to create two 
independent PWM signals, which are used to control the brightness of two 
LEDs on port P2.1 and P2.6. The program sets up two Compare Channels to 
provide asymmetrical PWM with a fixed frequency, but variable Duty Cycle. 
The selected frequency is high enough, so that the eye cannot recognize, 
that the LED is actually switched on and off alternately, but it sees 
different brightness according to different duty cycles. To show the 
independence of both Compare Channels, their Duty Cycles are varied in 
opposite directions. That means, while one LED turns brighter, the 
other one turns darker.