ATmega88 datasheet(125/340 Pages) ATMEL

125 / 340 page

125

7530H–AVR–02/09

ATmega48/88/168 Automotive

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

The extreme values for the OCR1x Register represents special cases when generating a PWM

waveform output in the phase correct PWM mode. If the OCR1x is set equal to BOTTOM the

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

non-inverted PWM mode. For inverted PWM the output will have the opposite logic values. If

OCR1A is used to define the TOP value (WGM13:0 = 9) and COM1A1:0 = 1, the OC1A output

will toggle with a 50% duty cycle.

14.9

Timer/Counter Timing Diagrams

The Timer/Counter is a synchronous design and the timer clock (clk

T1) is therefore shown as a

clock enable signal in the following figures. The figures include information on when Interrupt

Flags are set, and when the OCR1x Register is updated with the OCR1x buffer value (only for

modes utilizing double buffering). Figure 14-10 shows a timing diagram for the setting of OCF1x.

Figure 14-10. Timer/Counter Timing Diagram, Setting of OCF1x, no Prescaling

Figure 14-11 shows the same timing data, but with the prescaler enabled.

Figure 14-11. Timer/Counter Timing Diagram, Setting of OCF1x, with Prescaler (f

clk_I/O/8)

clk

(clk

I/O/1)

OCFnx

clk

I/O

OCRnx

TCNTn

OCRnx Value

OCRnx - 1

OCRnx

OCRnx + 1

OCRnx + 2

OCFnx

OCRnx

TCNTn

OCRnx Value

OCRnx - 1

OCRnx

OCRnx + 1

OCRnx + 2

clk

I/O

clk

(clk

I/O/8)

ATmega88 Datasheet(PDF) 125 Page - ATMEL Corporation

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