Rainbow-electronics ATmega8515L Manual do Utilizador descarregar pdf (Página 88)

ATmega8515(L)

2512A–AVR–04/02

as a strobe. Thereforeitis thevalue present in the COM01:0 bits that determines the

effectof the forcedcompare.

A FOC0 strobe will not generate any interrupt, norwill it clear thetimer in CTC mode

using OCR0 as TOP.

The FOC0 bit is always read aszero.

• Bit 6, 3 – WGM01:0: Waveform Generation Mode

These bitscontrol the counting sequenceof the counter, the source for themaximum

(TOP)counter value, andwhat typeofwaveform generation to beused. Modes of oper-

ation supportedbytheTimer/Counter unit are:Normal mode,Clear Timer on Compare

match (CTC) mode, and twotypes of Pulse WidthModulation (PWM) modes. See Table

44 and “Modes ofOperation” on page 82.

Note: 1. The CTC0and PWM0 bit definition names arenow obsolete. Usethe WGM01:0 def-

initions. However, the functionality andlocation of these bits are compatible with

previous versions of thetimer.

• Bit 5:4 – COM01:0: Compare Match Output Mode

These bitscontrol the Output Compare pin (OC0)behavior. If one orboth of the

COM01:0 bits are set, the OC0output overrides thenormalport functionality of the I/O

pin it isconnected to. However, note that the Data Direction Register(DDR)bit corre-

spondingtothe OC0 pin must be set in order to enablethe output driver.

When OC0isconnected to the pin, the function of the COM01:0 bitsdepends on the

WGM01:0 bit setting. Table45shows the COM01:0 bit functionalitywhen the WGM01:0

bits are settoanormal orCTC mode (non-PWM).

Table46shows the COM01:0 bit functionalitywhen the WGM01:0 bits are set to fast

PWM mode.

Table 44. Waveform Generation Mode Bit Description

(1)

Mode

WGM01

(CTC0)

WGM00

(PWM0)

Timer/Counter Mode

of Operation TOP

Update of

OCR0 at

TOV0 Flag

Set on

00 0Normal 0xFF Immediate MAX

10 1PWM, Phase Correct0xFF TOP BOTTOM

21 0CTCOCR0 Immediate MAX

3 11FastPWM 0xFF TOP MAX

Table 45. Compare Output Mode, non-PWM Mode

COM01 COM00 Description

00Normalportoperation,OC0 disconnected.

01Toggle OC0oncomparematch.

10ClearOC0oncomparematch.

11Set OC0oncomparematch.

1 2 ... 83 84 85 86 87 88 89 90 91 92 93 ... 222 223

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