ATMEGA8_08 Datasheet, PDF (96/308 Pages) ATMEL Corporation – 8-bit with 8K Bytes In-System Programmable Flash

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.
Figure 43. Timer/Counter Timing Diagram, no Prescaling
clk_I/O
clk_Tn
(clk_I/O/1)
TCNTn
(CTC and FPWM)
TCNTn
(PC and PFC PWM)
TOVn (FPWM)
and ICFn (if used
as TOP)
OCRnx
(Update at TOP)
TOP - 1
TOP - 1
TOP
TOP
Old OCRnx Value
BOTTOM
TOP - 1
BOTTOM + 1
TOP - 2
New OCRnx Value
Figure 44 shows the same timing data, but with the prescaler enabled.
Figure 44. Timer/Counter Timing Diagram, with Prescaler (f_{clk_I/O}/8)
clk_I/O
clk_Tn
(clk_I/O/8)
TCNTn
(CTC and FPWM)
TCNTn
(PC and PFC PWM)
TOVn (FPWM)
and ICFn (if used
as TOP)
OCRnx
(Update at TOP)
TOP - 1
TOP - 1
TOP
TOP
Old OCRnx Value
BOTTOM
BOTTOM + 1
TOP - 1
TOP - 2
New OCRnx Value
16-bit
Timer/Counter
Register
Description
Timer/Counter 1
Control Register A –
TCCR1A
Bit
Read/Write
7
COM1A1
R/W
6
COM1A0
R/W
5
COM1B1
R/W
4
COM1B0
R/W
3
FOC1A
W
2
FOC1B
W
1
WGM11
R/W
0
WGM10
R/W
TCCR1A
96 ATmega8(L)
2486T–AVR–05/08