abstract.txt

keil-C51完全破解版-28.7M.zip

LPC932 EXAMPLE:	CREATING A PWM SIGNAL USING A TIMER IN MODE 6
Christian Kulig, 12/06/02

INTRODUCTION:
The LPC932 can be used to create a Pulse Width Modulated PWM signal. That's an analog 
signal, with only 2 discrete levels, for example 0V and 5V and a  constant period. 
The current value of this signal at a certain point of time is proportional to its 
Duty Cycle. That's the High Time during one period divided by the period. It can also 
be calculated as 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 general purpose timer T1 of the LPC932 is set up to PWM Mode 6. In this mode it 
becomes a  8 bit up-counter with a special 8 bit reload on overflow. The reload 
values are alternating and represent the High Time and one period minus the High 
Time (=Low Time) of the PWM signal. On each overflow there can be an interrupt or a 
toggle of a certain port pin. 

The assigned port pin of T1 is P0.7.

The example alternately increases and decreases the Duty Cycle of the PWM signal on 
port pin P0.7 between 0% and 100%.

Please note, that on the Keil MCB900 Board this port pin is not connected to any of 
the LEDs, nevertheless the PWM can be displayed with a oscilloscope.