
72
ATtiny40 [DATASHEET]
8263B–AVR–01/2013
Note:
1. A special case occurs when OCR0A equals TOP and COM0A1 is set. In this case, the Compare Match is ignored,
Table 11-4 shows COM0A[1:0] bit functionality when WGM0[2:0] bits are set to phase correct PWM mode.
Note:
1. When OCR0A equals TOP and COM0A1 is set, the Compare Match is ignored, but the set or clear is done at TOP.
Bits 5:4 – COM0B[1:0]: Compare Match Output B Mode
These bits control the Output Compare pin (OC0B) behavior. If one or both of COM0B[1:0] bits are set, the OC0B
output overrides the normal port functionality of the I/O pin it is connected to. The Data Direction Register (DDR) bit
corresponding to the OC0B pin must be set in order to enable the output driver.
When OC0B is connected to the pin, the function of COM0B[1:0] bits depend on WGM0[2:0] bit setting.
Table 11-5shows COM0B[1:0] bit functionality when WGM0[2:0] bits are set to normal or CTC mode (non-PWM).
Table 11-3.
Compare Output Mode, Fast PWM Mode
(1)COM0A1
COM0A0
Description
0
Normal port operation, OC0A disconnected
01
WGM02 = 0: Normal Port Operation, OC0A Disconnected
WGM02 = 1: Toggle OC0A on Compare Match
10
Clear OC0A on Compare Match
Set OC0A at BOTTOM (non-inverting mode)
11
Set OC0A on Compare Match
Clear OC0A at BOTTOM (inverting mode)
Table 11-4.
Compare Output Mode, Phase Correct PWM Mod
eCOM0A1
COM0A0
Description
0
Normal port operation, OC0A disconnected.
01
WGM02 = 0: Normal Port Operation, OC0A Disconnected.
WGM02 = 1: Toggle OC0A on Compare Match.
10
Clear OC0A on Compare Match when up-counting. Set OC0A on
Compare Match when down-counting.
11
Set OC0A on Compare Match when up-counting. Clear OC0A on
Compare Match when down-counting.
Table 11-5.
Compare Output Mode, non-PWM Mode
COM0B1
COM0B0
Description
0
Normal port operation, OC0B disconnected.
0
1
Toggle OC0B on Compare Match
1
0
Clear OC0B on Compare Match
1
Set OC0B on Compare Match