
141
ATmega64A [DATASHEET]
8160D–AVR–02/2013
direction
Select between increment and decrement.
clear
Clear TCNT2 (set all bits to zero).
clk
Tn
Timer/counter clock, referred to as clk
T0 in the following.
top
Signalize that TCNT2 has reached maximum value.
bottom
Signalize that TCNT2 has reached minimum value (zero).
Depending of the mode of operation used, the counter is cleared, incremented, or decremented at each timer clock
(clk
T2). clkT2 can be generated from an external or internal clock source, selected by the Clock Select bits
(CS22:0). When no clock source is selected (CS22:0 = 0) the timer is stopped. However, the TCNT2 value can be
accessed by the CPU, regardless of whether clk
T2 is present or not. A CPU write overrides (has priority over) all
counter clear or count operations.
The counting sequence is determined by the setting of the WGM01 and WGM00 bits located in the Timer/Counter
Control Register (TCCR2). There are close connections between how the counter behaves (counts) and how
waveforms are generated on the Output Compare output OC2. For more details about advanced counting
The Timer/Counter Overflow Flag (TOV2) is set according to the mode of operation selected by the WGM21:0 bits.
TOV2 can be used for generating a CPU interrupt.
18.5
Output Compare Unit
The 8-bit comparator continuously compares TCNT2 with the Output Compare Register (OCR2). Whenever
TCNT2 equals OCR2, the comparator signals a match. A match will set the Output Compare Flag (OCF2) at the
next timer clock cycle. If enabled (OCIE2 = 1 and Global Interrupt Flag in SREG is set), the Output Compare Flag
generates an Output Compare interrupt. The OCF2 flag is automatically cleared when the interrupt is executed.
Alternatively, the OCF2 flag can be cleared by software by writing a logical one to its I/O bit location. The Wave-
form Generator uses the match signal to generate an output according to operating mode set by the WGM21:0 bits
and Compare Output mode (COM21:0) bits. The max and bottom signals are used by the Waveform Generator for