Datasheet

164
7766F–AVR–11/10
ATmega16/32U4
that the Data Direction Register (DDR) bit corresponding to the OC4B pin must be set in order to
enable the output driver.
The function of the COM4B1:0 bits depends on the PWM4B and WGM40 bit settings. Table 15-
11 shows the COM4B1:0 bit functionality when the PWM4B bit is set to Normal Mode (non-
PWM).
Table 15-12 shows the COM4B1:0 bit functionality when the PWM4B and WGM40 bits are set to
Fast PWM Mode.
Table 15-13 shows the COM4B1:0 bit functionality when the PWM4B and WGM40 bits are set to
Phase and Frequency Correct PWM Mode.
• Bit 3 - FOC4A: Force Output Compare Match 4A
The FOC4A bit is only active when the PWM4A bit specify a non-PWM mode.
Writing a logical one to this bit forces a change in the Waveform Output (OCW4A) and the Out-
put Compare pin (OC4A) according to the values already set in COM4A1 and COM4A0. If
COM4A1 and COM4A0 written in the same cycle as FOC4A, the new settings will be used. The
Force Output Compare bit can be used to change the output pin value regardless of the timer
Table 15-11. Compare Output Mode, Normal Mode (non-PWM)
COM4B1..0 OCW4B Behavior OC4B Pin OC4B Pin
00 Normal port operation. Disconnected Disconnected
01 Toggle on Compare Match. Connected Disconnected
10 Clear on Compare Match. Connected Disconnected
11 Set on Compare Match. Connected Disconnected
Table 15-12. Compare Output Mode, Fast PWM Mode
COM4B1..0 OCW4B Behavior OC4B Pin OC4B Pin
00 Normal port operation. Disconnected Disconnected
01
Cleared on Compare Match.
Set when TCNT4 = 0x000.
Connected Connected
10
Cleared on Compare Match.
Set when TCNT4 = 0x000.
Connected Disconnected
11
Set on Compare Match.
Cleared when TCNT4 = 0x000.
Connected Disconnected
Table 15-13. Compare Output Mode, Phase and Frequency Correct PWM Mode
COM4B1..0 OCW4B Behavior OC4B Pin OC4B Pin
00 Normal port operation. Disconnected Disconnected
01
Cleared on Compare Match when up-counting.
Set on Compare Match when down-counting.
Connected 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