AT90SCR100 datasheet(92/433 Pages) ATMEL

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TPR0327AY–SMS–30Jan09

AT90SCR100

Figure 13-4.

Compare Match Output Unit, Schematic

The general I/O port function is overridden by the Output Compare (OC0x) from the Waveform

Generator if either of the COM0x1:0 bits are set. However, the OC0x pin direction (input or out-

put) is still controlled by the Data Direction Register (DDR) for the port pin. The Data Direction

visible on the pin. The port override function is independent of the Waveform Generation mode.

The design of the Output Compare pin logic allows the initialization of the OC0x state before the

output is enabled. Note that some COM0x1:0 bit settings are reserved for certain modes of oper-

ation. See “8-bit Timer/Counter0 Register Description” on page 98.

13.1.6

Compare Output Mode and Waveform Generation

The Waveform Generator uses the COM0x1:0 bits differently in Normal, CTC, and PWM modes.

For all modes, setting the COM0x1:0 = 0 instructs the Waveform Generator that no action on the

OC0x Register is to be performed on the next Compare Match. For compare output actions in

the non-PWM modes refer to Table 13-2 on page 99. For fast PWM mode, refer to Table 13-3 on

page 99, and for phase correct PWM refer to Table 13-4 on page 99.

A change of the COM0x1:0 bits state will have an effect at the first Compare Match after the bits

are written. For non-PWM modes, the action can be forced to have an immediate effect by using

the FOC0x strobe bits.

13.1.7

Modes of Operation

The mode of operation, i.e., the behavior of the Timer/Counter and the Output Compare pins, is

defined by the combination of the Waveform Generation mode (WGM02:0) and the Compare

Output mode (COM0x1:0) bits. The Compare Output mode bits do not affect the counting

sequence, while the Waveform Generation mode bits do. The COM0x1:0 bits control whether

the PWM output generated should be inverted or not (inverted or non-inverted PWM). For non-

PWM modes the COM0x1:0 bits control whether the output should be set, cleared, or toggled at

a Compare Match (See “Compare Match Output Unit” on page 91.).

For detailed timing information see “Timer/Counter Timing Diagrams” on page 97.

PORT

DDR

OC0x

Waveform

Generator

COM0x1

COM0x0

FOC0n

clk

I/O

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