Rainbow-electronics ATmega8515L Uživatelský manuál stáhnout pdf (Strana 84)

ATmega8515(L)

2512A–AVR–04/02

Figure 38. FastPWM Mode, Timing Diagram

TheTimer/CounterOverflowFlag (TOV0) isset each time the counterreachesMAX. If

theinterruptis enabled, theinterrupt handlerroutine can beusedfor updating the com-

parevalue.

In fastPWM mode, the compare unit allows generation of PWM waveforms on the OC0

pin. Setting the COM01:0 bits to 2 will produceanon-inverted PWM and an inverted

PWM output can be generatedbysetting the COM01:0to3(See Table46 on page 89).

TheactualOC0value will only bevisibleonthe port pin if the data direction for the port

pin isset as output. ThePWM waveformis generatedbysetting (orclearing) the OC0

OC0Register at thetimerclock cyclethe counter iscleared(changesfrom MAX to

BOTTOM).

ThePWM frequency for the output can be calculatedbythe following equation:

The“

”variable represents the prescale factor(1, 8,64, 256, or 1024).

Theextreme valuesfor the OCR0 Registerrepresentsspecialcaseswhen generating a

PWM waveformoutput in the fastPWM mode. If the OCR0 isset equal to BOTTOM, the

output will beanarrowspike for each MAX+1timerclock cycle. Setting the OCR0 equal

to MAXwill resultinaconstantly high orlow output (dependingonthe polarity of the out-

put set by the COM01:0 bits).

A frequency (with 50%duty cycle)waveform output in fastPWM mode can beachieved

by setting OC0totoggleitslogicallevel on each comparematch (COM01:0 = 1).The

waveformgeneratedwill have a maximum frequency off

OC0

clk_I/O

/2 when OCR0 is

set to zero. Thisfeatureissimilar to the OC0toggleinCTC mode, exceptthe double

bufferfeatureof theoutput compareunitis enabled in the fastPWM mode.

TCNTn

OCRn Update and

TOVn Interrupt Flag Set

Period

2 3

OCn

(COMn1:0 = 2)

(COMn1:0 = 3)

OCRn Interrupt Flag Set

4 5 6 7

OCnPWM

clk_I/O

N 256⋅

------------------=

1 2 ... 79 80 81 82 83 84 85 86 87 88 89 ... 222 223

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