PCIF0 datasheet(131/294 Pages) ATMEL

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9219A–RFID–01/11

Atmel ATA5505 [Preliminary]

It is recommended to use the phase and frequency correct mode instead of the phase correct

mode when changing the TOP value while the Timer/Counter is running. When using a static

TOP value there are practically no differences between the two modes of operation.

In phase correct PWM mode, the compare units allow generation of PWM waveforms on the

OC1A/B pins. Setting the COM1A/B1:0 bits to two will produce a non-inverted PWM and an

inverted PWM output can be generated by setting the COM1A/B1:0 to three (See Table on

page 136). The actual OC1A/B value will only be visible on the port pin if the data direction for

the port pin is set as output (DDR_OC1A/B) and OC1A/Bi is set. The PWM waveform is gener-

ated by setting (or clearing) the OC1A/B Register at the compare match between OCR1A/B

and TCNT1 when the counter increments, and clearing (or setting) the OC1A/B Register at

compare match between OCR1A/B and TCNT1 when the counter decrements. The PWM fre-

quency for the output when using phase correct PWM can be calculated by the following

equation:

The N variable represents the prescaler divider (1, 8, 64, 256, or 1024).

The extreme values for the OCR1A/B Register represent special cases when generating a

PWM waveform output in the phase correct PWM mode. If the OCR1A/B is set equal to BOT-

TOM the output will be continuously low and if set equal to TOP the output will be continuously

high for non-inverted PWM mode. For inverted PWM the output will have the opposite logic

values.

12.9.5

Phase and Frequency Correct PWM Mode

The phase and frequency correct Pulse Width Modulation, or phase and frequency correct

PWM mode (WGM13:0 = 8 or 9) provides a high resolution phase and frequency correct PWM

waveform generation option. The phase and frequency correct PWM mode is, like the phase

correct PWM mode, based on a dual-slope operation. The counter counts repeatedly from

BOTTOM (0x0000) to TOP and then from TOP to BOTTOM. In non-inverting Compare Output

mode, the Output Compare (OC1A/B) is cleared on the compare match between TCNT1 and

OCR1A/B while upcounting, and set on the compare match while downcounting. In inverting

Compare Output mode, the operation is inverted. The dual-slope operation gives a lower max-

imum operation frequency compared to the single-slope operation. However, due to the

symmetric feature of the dual-slope PWM modes, these modes are preferred for motor control

applications.

The main difference between the phase correct, and the phase and frequency correct PWM

mode is the time the OCR1A/B Register is updated by the OCR1A/B Buffer Register, (see Fig-

ure 12-9 and Figure 12-10).

The PWM resolution for the phase and frequency correct PWM mode can be defined by either

ICR1 or OCR1A. The minimum resolution allowed is 2-bit (ICR1 or OCR1A set to 0x0003),

and the maximum resolution is 16-bit (ICR1 or OCR1A set to MAX). The PWM resolution in

bits can be calculated using the following equation:

fOCnxPCPWM

clk_I/O

NTOP

⋅⋅

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

RPFCPWM

TOP 1

()

log

()

log

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

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