AT89LP51RB2 datasheet(86/254 Pages) ATMEL

86 / 254 page

3722A–MICRO–10/11

AT89LP51RB2/RC2/IC2 Preliminary

Figure 13-9. PWM Mode 2 Waveform

13.6.4

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 13-10. 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

ch a nn els a nd a n e x t r a time r o r co u nt er. With T i me r 0 in PWM M o d e 3 , th e

AT89LP51RB2/RC2/IC2 can appear to have four 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 following formulas give the output frequency and duty cycle for

Timer 0 in PWM Mode 3.

Note:

In Fast Mode, TPS applies only when the TnX2 bits in CKCON0 are set. TPS always

applies in Compatibility Mode, therefore setting TnX2 in Compatibility Mode will halve

the output frequency.

THx

FFh

Mode 3:

out

fSYS

256

-----------

TPS

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

Mode 3, T0:

Duty Cycle %

100

RL0

256

-----------

Mode 3, T1:

Duty Cycle %

100

RH0

256

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

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