ATmega325PA Atmel Corporation, ATmega325PA Datasheet - Page 128

• Manufacturer Part Number: ATmega325PA
• Manufacturer: Atmel Corporation

16.10 Timer/Counter Timing Diagrams
8285D–AVR–06/11
ATmega165A/PA/325A/PA/3250A/PA/645A/P/6450A/P
The extreme values for the OCR1x Register represents special cases when generating a PWM
waveform output in the phase and frequency 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 val-
ues. If OCR1A is used to define the TOP value (WGM1[3:0] = 9) and COM1A1:0 = 1, the OC1A
output will toggle with a 50% duty cycle.
The Timer/Counter is a synchronous design and the timer clock (clk
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 16-10. Timer/Counter Timing Diagram, Setting of OCF1x, no Prescaling
Figure 16-11
Figure 16-11. Timer/Counter Timing Diagram, Setting of OCF1x, with Prescaler (f
Figure 16-12
frequency correct PWM mode the OCR1x Register is updated at BOTTOM. The timing diagrams
will be the same, but TOP should be replaced by BOTTOM, TOP-1 by BOTTOM+1 and so on.
The same renaming applies for modes that set the TOV1 Flag at BOTTOM.
TCNTn
OCRnx
OCFnx
TCNTn
OCRnx
(clk
OCFnx
(clk
clk
clk
clk
clk
I/O
I/O
I/O
Tn
I/O
Tn
/1)
/8)
shows the same timing data, but with the prescaler enabled.
shows the count sequence close to TOP in various modes. When using phase and
OCRnx - 1
OCRnx - 1
Figure 16-10
OCRnx
OCRnx
OCRnx Value
OCRnx Value
shows a timing diagram for the setting of OCF1x.
OCRnx + 1
OCRnx + 1
T1
) is therefore shown as a
OCRnx + 2
OCRnx + 2
clk_I/O
/8)
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