AT89LP51RB2 datasheet(103/254 Pages) ATMEL

103 / 254 page

103

3722A–MICRO–10/11

AT89LP51RB2/RC2/IC2 Preliminary

15.6

Pulse Width Modulator Mode

All of the PCA modules can be used as PWM outputs. Figure 15-7 shows the PWM function.

The frequency of the output depends on the source for the PCA timer. All of the modules will

have the same frequency of output because they all share the PCA timer. The duty cycle of each

module is independently variable using the modules capture register CCAPnL. When the value

of the PCA CL SFR is less than the value in the modules CCAPnL SFR the output will be low,

when it is equal to or greater than the output will be high. When CL overflows from FFH to 00H,

CCAPnL is reloaded with the value in CCAPnH. This allows updating the PWM without glitches.

The PWM and ECOM bits in the module's CCAPMn register must be set to enable the PWM

mode. The following equations show the resulting frequency and duty cycles of the generated

output:

Figure 15-7. PCA PWM Mode

An example PCA PWM waveform is shown in Figure 15-8.

Figure 15-8. PCA PWM Waveform

CPS

00B:

out

fSYS

256

-----------

TPS

---------------------

Duty Cycle %

100

256

CCAPnL

–

256

---------------------------------------

CCAPnH

CCAPnL

ECOMn

PWMn

CCAPMn.1

Module n

CEXn

–

ECOMn

CCAPMn.6

CL = FFH

PWMn = 1, ECOMn = 1

CCAPnH

CEXn

CL = 00H

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