Rainbow Electronics ATmega162V - Manual (Page 91)

91
ATmega162/V
2513E–AVR–09/03
Figure 35 shows a block diagram of the output compare unit.
Figure 35. Output Compare Unit, Block Diagram
The OCR0 Register is double buffered when using any of the Pulse Width Modulation
(PWM) modes. For the Normal and Clear Timer on Compare (CTC) modes of operation,
the double buffering is disabled. The double buffering synchronizes the update of the
OCR0 Compare Register to either top or bottom of the counting sequence. The synchro-
nization prevents the occurrence of odd-length, non-symmetrical PWM pulses, thereby
making the output glitch-free.
The OCR0 Register access may seem complex, but this is not case. When the double
buffering is enabled, the CPU has access to the OCR0 Buffer Register, and if double
buffering is disabled the CPU will access the OCR0 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 (FOC0) bit. Forcing Compare
Match will not set the OCF0 Flag or reload/clear the Timer, but the OC0 pin will be
updated as if a real Compare Match had occurred (the COM01:0 bits settings define
whether the OC0 pin is set, cleared or toggled).
Compare Match Blocking by
TCNT0 Write All CPU write operations to the TCNT0 Register will block any Compare Match that
occur in the next timer clock cycle, even when the timer is stopped. This feature allows
OCR0 to be initialized to the same value as TCNT0 without triggering an interrupt when
the Timer/Counter clock is enabled.
OCFn (Int.Req.)
=
(8-bit Comparator )
OCRn
OCn
DATA BUS
TCNTn
WGMn1:0
Waveform Generator
top
FOCn
COMn1:0
bottom