110
7679H–CAN–08/08
AT90CAN32/64/128
• Bit 6, 3 – WGM01:0: Waveform Generation Mode
These bits control the counting sequence of the counter, the source for the maximum (TOP)
counter value, and what type of waveform generation to be used. Modes of operation supported
by the Timer/Counter unit are: Normal mode, Clear Timer on Compare match (CTC) mode, and
two types of Pulse Width Modulation (PWM) modes. See Table 12-1 and “Modes of Operation”
on page 104.
Note: 1. The CTC0 and PWM0 bit definition names are now obsolete. Use the WGM01:0 definitions.
However, the functionality and location of these bits are compatible with previous versions of
the timer.
• Bit 5:4 – COM01:0: Compare Match Output Mode
These bits control the Output Compare pin (OC0A) behavior. If one or both of the COM0A1:0
bits are set, the OC0A output overrides the normal port functionality of the I/O pin it is connected
to. However, note that the Data Direction Register (DDR) bit corresponding to the OC0A pin
must be set in order to enable the output driver.
When OC0A is connected to the pin, the function of the COM0A1:0 bits depends on the
WGM01:0 bit setting. Table 12-2 shows the COM0A1:0 bit functionality when the WGM01:0 bits
are set to a normal or CTC mode (non-PWM).
Table 12-3 shows the COM0A1:0 bit functionality when the WGM01:0 bits are set to fast PWM
mode.
Table 12-1. Waveform Generation Mode Bit Description
(1)
Mode
WGM01
(CTC0)
WGM00
(PWM0)
Timer/Counter
Mode of Operation
TOP
Update of
OCR0A at
TOV0 Flag
Set on
0 0 0 Normal 0xFF Immediate MAX
1 0 1 PWM, Phase Correct 0xFF TOP BOTTOM
2 1 0 CTC OCR0A Immediate MAX
3 1 1 Fast PWM 0xFF TOP MAX
Table 12-2. Compare Output Mode, non-PWM Mode
COM0A1 COM0A0 Description
0 0 Normal port operation, OC0A disconnected.
0 1 Toggle OC0A on compare match
1 0 Clear OC0A on compare match
1 1 Set OC0A on compare match
Table 12-3. Compare Output Mode, Fast PWM Mode
(1)
COM0A1 COM0A0 Description
0 0 Normal port operation, OC0A disconnected.
01Reserved
10
Clear OC0A on compare match.
Set OC0A at TOP
11
Set OC0A on compare match.
Clear OC0A at TOP
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