AT89LP216-20PI datasheet(35/90 Pages) ATMEL

35 / 90 page

3621A–MICRO–6/06

AT89LP216 [Preliminary]

14.5.4

Mode 3 – Split 8-bit PWM

Timer 1 in PWM Mode 3 simply holds its count. The effect is the same as setting TR1 = 0.

Timer 0 in PWM Mode 3 establishes TL0 and TH0 as two separate PWM counters in a manner

similar to normal Mode 3. PWM Mode 3 on Timer 0 is shown in Figure 14-9. Only the Timer

Prescaler is available to change the output frequency during PWM Mode 3. TL0 can use the

Timer 0 control bits: GATE, TR0, INT0, PWM0EN and TF0. TH0 is locked into a timer function

and uses TR1, PWM1EN and TF1. RL0 provides the duty cycle for TL0 and RH0 provides the

duty cycle for TH0.

PWM Mode 3 is for applications requiring a single PWM channel and two timers, or two PWM

channels and an extra timer or counter. With Timer 0 in PWM Mode 3, the AT89LP216 can

appear to have three Timer/Counters. When Timer 0 is in PWM Mode 3, Timer 1 can be turned

on and off by switching it out of and into its own Mode 3. In this case, Timer 1 can still be used by

the serial port as a baud rate generator or in any application not requiring an interrupt. The fol-

lowing formulas give the output frequency and duty cycle for Timer 0 in PWM Mode 3.

Figure 14-9. Timer/Counter 0 PWM Mode 3

Mode 3:

fout

Oscillator Frequency

256

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

TPS 1

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

Mode 3, T0:

Duty Cycle %

100

RL0

256

-----------

Mode 3, T1:

Duty Cycle %

100

RH0

256

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

OSC

TR1

GATE

INT1 Pin

Control

TL0

(8 Bits)

OCR0

RL0

(8 Bits)

OSC

TH0

(8 Bits)

OCR1

RH0

(8 Bits)

TR1

÷TPS

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