Atmega169v/l – Rainbow Electronics Atmega169L User Manual
Page 135
135
ATmega169V/L
2514A–AVR–08/02
• Bit 5:4 – COM2A1:0: Compare Match Output Mode A
These bits control the Output Compare pin (OC2A) behavior. If one or both of the
COM2A1:0 bits are set, the OC2A output overrides the normal port functionality of the
I/O pin it is connected to. However, note that the Data Direction Register (DDR) bit cor-
responding to OC2A pin must be set in order to enable the output driver.
When OC2A is connected to the pin, the function of the COM2A1:0 bits depends on the
WGM21:0 bit setting. Table 62 shows the COM2A1:0 bit functionality when the
WGM21:0 bits are set to a normal or CTC mode (non-PWM).
Table 63 shows the COM2A1:0 bit functionality when the WGM21:0 bits are set to fast
PWM mode.
Note:
1. A special case occurs when OCR2A equals TOP and COM2A1 is set. In this case,
the compare match is ignored, but the set or clear is done at TOP. See “Fast PWM
Mode” on page 129 for more details.
Table 64 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 OCR2A equals TOP and COM2A1 is set. In this case,
the compare match is ignored, but the set or clear is done at TOP. See “Phase Cor-
rect PWM Mode” on page 130 for more details.
Table 62. Compare Output Mode, non-PWM Mode
COM2A1
COM2A0
Description
0
0
Normal port operation, OC2A disconnected.
0
1
Toggle OC2A on compare match.
1
0
Clear OC2A on compare match.
1
1
Set OC2A on compare match.
Table 63. Compare Output Mode, Fast PWM Mode
(1)
COM2A1
COM2A0
Description
0
0
Normal port operation, OC2A disconnected.
0
1
Reserved
1
0
Clear OC2A on compare match, set OC2A at TOP.
1
1
Set OC2A on compare match, clear OC2A at TOP.
Table 64. Compare Output Mode, Phase Correct PWM Mode
(1)
COM2A1
COM2A0
Description
0
0
Normal port operation, OC2A disconnected.
0
1
Reserved
1
0
Clear OC2A on compare match when up-counting. Set OC2A on
compare match when downcounting.
1
1
Set OC2A on compare match when up-counting. Clear OC2A on
compare match when downcounting.