ATmega16 datasheet(120/357 Pages) ATMEL

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2466S–AVR–05/09

ATmega16(L)

to either top or bottom of the counting sequence. The synchronization prevents the occurrence

of odd-length, non-symmetrical PWM pulses, thereby making the output glitch-free.

The OCR2 Register access may seem complex, but this is not case. When the double buffering

is enabled, the CPU has access to the OCR2 Buffer Register, and if double buffering is disabled

the CPU will access the OCR2 directly.

Force Output

Compare

In non-PWM waveform generation modes, the match output of the comparator can be forced by

writing a one to the Force Output Compare (FOC2) bit. Forcing compare match will not set the

OCF2 Flag or reload/clear the timer, but the OC2 pin will be updated as if a real compare match

had occurred (the COM21:0 bits settings define whether the OC2 pin is set, cleared or toggled).

Compare Match

Blocking by TCNT2

Write

All CPU write operations to the TCNT2 Register will block any compare match that occurs in the

next timer clock cycle, even when the timer is stopped. This feature allows OCR2 to be initialized

to the same value as TCNT2 without triggering an interrupt when the Timer/Counter clock is

enabled.

Using the Output

Compare Unit

Since writing TCNT2 in any mode of operation will block all compare matches for one timer clock

cycle, there are risks involved when changing TCNT2 when using the output compare unit, inde-

pendently of whether the Timer/Counter is running or not. If the value written to TCNT2 equals

the OCR2 value, the compare match will be missed, resulting in incorrect waveform generation.

Similarly, do not write the TCNT2 value equal to BOTTOM when the counter is downcounting.

The setup of the OC2 should be performed before setting the Data Direction Register for the port

pin to output. The easiest way of setting the OC2 value is to use the Force Output Compare

(FOC2) strobe bit in Normal mode. The OC2 Register keeps its value even when changing

between Waveform Generation modes.

Be aware that the COM21:0 bits are not double buffered together with the compare value.

Changing the COM21:0 bits will take effect immediately.

ATmega16 датащи(PDF) 120 Page - ATMEL Corporation