
114
2588F–AVR–06/2013
ATtiny261/461/861
Bits 5,4 – COM1B1, COM1B0: Comparator B Output Mode, Bits 1 and 0
These bits control the behaviour of the Waveform Output (OCW1B) and the connection of the
Output Compare pin (OC1B). If one or both of the COM1B1:0 bits are set, the OC1B output
overrides the normal port functionality of the I/O pin it is connected to. The complementary
OC1B output is connected only in PWM modes when the COM1B1:0 bits are set to “01”. Note
that the Data Direction Register (DDR) bit corresponding to the OC1B pin must be set in order to
enable the output driver.
The function of the COM1B1:0 bits depends on the PWM1B and WGM11:10 bit settings.
Table12-13 shows the COM1B1:0 bit functionality when the PWM1B bit is set to Normal Mode (non-
PWM).
Table 12-14 shows the COM1B1:0 bit functionality when the PWM1B and WGM11:10 bits are
set to Fast PWM Mode.
Table 12-15 shows the COM1B1:0 bit functionality when the PWM1B and WGM11:10 bits are
set to Phase and Frequency Correct PWM Mode.
Bits COM1B1 and COM1B0 are shadowed in TCCR1C. Writing to bits COM1B1 and COM1B0
will also change bits COM1B1S and COM1B0S in TCCR1C. Similary, changes written to bits
Table 12-13. Compare Output Mode, Normal Mode (non-PWM)
COM1B1:0
OCW1B Behaviour
OC1B Pin
00
Normal port operation.
Disconnected
01
Toggle on Compare Match.
Connected
Disconnected
10
Clear on Compare Match.
Connected
Disconnected
11
Set on Compare Match.
Connected
Disconnected
Table 12-14. Compare Output Mode, Fast PWM Mode
COM1B1:0
OCW1B Behaviour
OC1B Pin
00
Normal port operation.
Disconnected
01
Cleared on Compare Match.
Set when TCNT1 = 0x000.
Connected
10
Cleared on Compare Match.
Set when TCNT1 = 0x000.
Connected
Disconnected
11
Set on Compare Match.
Cleared when TCNT1 = 0x000.
Connected
Disconnected
Table 12-15. Compare Output Mode, Phase and Frequency Correct PWM Mode
COM1B1:0
OCW1B Behaviour
OC1B Pin
00
Normal port operation.
Disconnected
01
Cleared on Compare Match when up-counting.
Set on Compare Match when down-counting.
Connected
10
Cleared on Compare Match when up-counting.
Set on Compare Match when down-counting.
Connected
Disconnected
11
Set on Compare Match when up-counting.
Cleared on Compare Match when down-counting.
Connected
Disconnected