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.
Timer/Counter Timing
Diagrams
The Timer/Counter is a synchronous design and the timer clock (clkT1) 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 49 shows a timing
diagram for the setting of OCF1x.
Figure 49. Timer/Counter Timing Diagram, Setting of OCF1x, No Prescaling
clkI/O
clkTn
(clkI/O/1)
TCNTn
OCRnx
OCFnx
OCRnx - 1
OCRnx
OCRnx + 1
OCRnx + 2
OCRnx Value
Figure 50 shows the same timing data, but with the prescaler enabled.
Figure 50. Timer/Counter Timing Diagram, Setting of OCF1x, with Prescaler (fclk_I/O/8)
clkI/O
clkTn
(clkI/O/8)
TCNTn
OCRnx
OCFnx
OCRnx - 1
OCRnx
OCRnx + 1
OCRnx + 2
OCRnx Value
102
ATmega16(L)
2466E–AVR–10/02
ATMEL [ ATMEL ]
