Datasheet

92
ATmega8A [DATASHEET]
8159E–AVR–02/2013
Figure 17-12. Timer/Counter Timing Diagram, no Prescaling
Figure 17-13 shows the same timing data, but with the prescaler enabled.
Figure 17-13. Timer/Counter Timing Diagram, with Prescaler (f
clk_I/O
/8)
17.11 Register Description
17.11.1 TCCR1A – Timer/Counter 1 Control Register A
• Bit 7:6 – COM1A1:0: Compare Output Mode for channel A
• Bit 5:4 – COM1B1:0: Compare Output Mode for channel B
The COM1A1:0 and COM1B1:0 control the Output Compare Pins (OC1A and OC1B respectively) behavior. If one
or both of the COM1A1:0 bits are written to one, the OC1A output overrides the normal port functionality of the I/O
TOVn (FPWM)
and ICFn (if used
as TOP)
OCRnx
(Update at TOP)
TCNTn
(CTC and FPWM)
TCNTn
(PC and PFC PWM)
TOP - 1 TOP TOP - 1 TOP - 2
Old OCRnx Value New OCRnx Value
TOP - 1 TOP BOTTOM BOTTOM + 1
clk
Tn
(clk
I/O
/1)
clk
I/O
TOVn (FPWM)
and ICFn (if used
as TOP)
OCRnx
(Update at TOP)
TCNTn
(CTC and FPWM)
TCNTn
(PC and PFC PWM)
TOP - 1 TOP TOP - 1 TOP - 2
Old OCRnx Value New OCRnx Value
TOP - 1 TOP BOTTOM BOTTOM + 1
clk
I/O
clk
Tn
(clk
I/O
/8)
Bit 76543210
COM1A1 COM1A0 COM1B1 COM1B0 FOC1A FOC1B WGM11 WGM10 TCCR1A
Read/Write R/W R/W R/W R/W W W R/W R/W
Initial Value00000000