Atmega8515(l) – Rainbow Electronics ATmega8515L User Manual
Page 88
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ATmega8515(L)
2512A–AVR–04/02
as a strobe. Therefore it is the value present in the COM01:0 bits that determines the
effect of the forced compare.
A FOC0 strobe will not generate any interrupt, nor will it clear the timer in CTC mode
using OCR0 as TOP.
The FOC0 bit is always read as zero.
• 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 oper-
ation 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
44 and “Modes of Operation” on page 82.
Note:
1. The CTC0 and PWM0 bit definition names are now obsolete. Use the WGM01:0 def-
initions. 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 (OC0) behavior. If one or both of the
COM01:0 bits are set, the OC0 output overrides the normal port functionality of the I/O
pin it is connected to. However, note that the Data Direction Register (DDR) bit corre-
sponding to the OC0 pin must be set in order to enable the output driver.
When OC0 is connected to the pin, the function of the COM01:0 bits depends on the
WGM01:0 bit setting. Table 45 shows the COM01:0 bit functionality when the WGM01:0
bits are set to a normal or CTC mode (non-PWM).
Table 46 shows the COM01:0 bit functionality when the WGM01:0 bits are set to fast
PWM mode.
Table 44. Waveform Generation Mode Bit Description
Mode
WGM01
(CTC0)
WGM00
(PWM0)
Timer/Counter Mode
of Operation
TOP
Update of
OCR0 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
OCR0
Immediate
MAX
3
1
1
Fast PWM
0xFF
TOP
MAX
Table 45. Compare Output Mode, non-PWM Mode
COM01
COM00
Description
0
0
Normal port operation, OC0 disconnected.
0
1
Toggle OC0 on compare match.
1
0
Clear OC0 on compare match.
1
1
Set OC0 on compare match.