Atmel ATmega128 User Manual

158
2467S–AVR–07/09
ATmega128
Table 66 shows the COM21:0 bit functionality when the WGM21:0 bits are set to fast PWM
mode.
Note: 1. A special case occurs when OCR2 equals TOP and COM21 is set. In this case, the compare
match is ignored, but the set or clear is done at BOTTOM. See “Fast PWM Mode” on page 152
for more details.
Table 67 shows the COM21:0 bit functionality when the WGM21:0 bits are set to phase correct
PWM mode.
Note: 1. A special case occurs when OCR2 equals TOP and COM21 is set. In this case, the compare
match is ignored, but the set or clear is done at TOP. See “Phase Correct PWM Mode” on page
153 for more details.
• Bit 2:0 – CS22:0: Clock Select
The three clock select bits select the clock source to be used by the Timer/Counter.
Table 65. Compare Output Mode, Non-PWM Mode
COM21 COM20 Description
0 0 Normal port operation, OC2 disconnected.
0 1 Toggle OC2 on compare match
1 0 Clear OC2 on compare match
1 1 Set OC2 on compare match
Table 66. Compare Output Mode, Fast PWM Mode
(1)
COM21 COM20 Description
0 0 Normal port operation, OC2 disconnected.
01Reserved
1 0 Clear OC2 on compare match, set OC2 at BOTTOM,
(non-inverting mode)
1 1 Set OC2 on compare match, clear OC2 at BOTTOM,
(inverting mode)
Table 67. Compare Output Mode, Phase Correct PWM Mode
(1)
COM21 COM20 Description
0 0 Normal port operation, OC2 disconnected.
01Reserved
1 0 Clear OC2 on compare match when up-counting. Set OC2 on compare
match when downcounting.
1 1 Set OC2 on compare match when up-counting. Clear OC2 on compare
match when downcounting.
Table 68. Clock Select Bit Description
CS22 CS21 CS20 Description
0 0 0 No clock source (Timer/Counter stopped)
001clk
I/O
/(No prescaling)
010clk
I/O
/8 (From prescaler)
011clk
I/O
/64 (From prescaler)
100clk
I/O
/256 (From prescaler)

Atmel ATmega128 Specifications

General

Brand	Atmel
Model	ATmega128
Category	Microcontrollers
Language	English