PCINT9 datasheet(97/294 Pages) ATMEL

97 / 294 page

9219A–RFID–01/11

Atmel ATA5505 [Preliminary]

For generating a waveform output in CTC mode, the OC0A output can be set to toggle its log-

ical level on each compare match by setting the Compare Output mode bits to toggle mode

(COM0A1:0 = 1). The OC0A value will not be visible on the port pin unless the data direction

for the pin is set to output. The waveform generated will have a maximum frequency of

OC0A =fclk_I/O/2 when OCR0A is set to zero (0x00). The waveform frequency is defined by the

following equation:

The N variable represents the prescale factor (1, 8, 32, 64, 128, 256, or 1024).

As for the Normal mode of operation, the TOV0 flag is set in the same timer clock cycle that

the counter counts from MAX to 0x00.

10.7.3

Fast PWM Mode

The fast Pulse Width Modulation or fast PWM mode (WGM01:0 = 3) provides a high frequency

PWM waveform generation option. The fast PWM differs from the other PWM option by its sin-

gle-slope operation. The counter counts from BOTTOM to MAX then restarts from BOTTOM.

In non-inverting Compare Output mode, the Output Compare (OC0A) is cleared on the com-

pare match between TCNT0 and OCR0A, and set at BOTTOM. In inverting Compare Output

mode, the output is set on compare match and cleared at BOTTOM. Due to the single-slope

operation, the operating frequency of the fast PWM mode can be twice as high as the phase

correct PWM mode that uses dual-slope operation. This high frequency makes the fast PWM

mode well suited for power regulation, rectification, and DAC applications. High frequency

allows physically small sized external components (coils, capacitors), and therefore reduces

total system cost.

In fast PWM mode, the counter is incremented until the counter value matches the MAX value.

The counter is then cleared at the following timer clock cycle. The timing diagram for the fast

PWM mode is shown in Figure 10-6. The TCNT0 value is in the timing diagram shown as a

histogram for illustrating the single-slope operation. The diagram includes non-inverted and

inverted PWM outputs. The small horizontal line marks on the TCNT0 slopes represent com-

pare matches between OCR0A and TCNT0.

Figure 10-6. Fast PWM Mode, Timing Diagram

fOCnx

clk_I/O

OCRnx

()

⋅⋅

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

TCNTn

OCRnx Update and

TOVn Interrupt Flag Set

Period

OCnx

(COMnx1:0 = 2)

(COMnx1:0 = 3)

OCRnx Interrupt Flag Set

PCINT9 Datasheet(PDF) 97 Page - ATMEL Corporation

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