User Manual

130
ATmega48A/PA/88A/PA/168A/PA/328/P [DATASHEET]
8271E–AVR–07/2012
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.
16.10 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 Reg-
ister is updated with the OCR1x buffer value (only for modes utilizing double buffering). Figure 16-10 shows a
timing diagram for the setting of OCF1x.
Figure 16-10. Timer/Counter Timing Diagram, Setting of OCF1x, no Prescaling
Figure 16-11 shows the same timing data, but with the prescaler enabled.
Figure 16-11. Timer/Counter Timing Diagram, Setting of OCF1x, with Prescaler (f
clk_I/O
/8)
Figure 16-12 on page 131 shows the count sequence close to TOP in various modes. When using phase and fre-
quency 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.
clk
Tn
(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
Tn
(clk
I/O
/8)