Datasheet

138
7593L–AVR–09/12
AT90USB64/128
Note: A special case occurs when OCRnA/OCRnB/OCRnC equals TOP and
COMnA1/COMnB1//COMnC1 is set. See “Phase correct PWM mode” on page 106. for more
details.
• Bit 1:0 – WGMn1:0: Waveform Generation mode
Combined with the WGMn3:2 bits found in the TCCRnB Register, these bits control the counting
sequence of the counter, the source for maximum (TOP) counter value, and what type of wave-
form generation to be used, see Table 15-4 on page 138. Modes of operation supported by the
Timer/Counter unit are: Normal mode (counter), Clear Timer on Compare match (CTC) mode,
and three types of Pulse Width Modulation (PWM) modes. (See “Modes of operation” on page
103.).
Table 15-3. Compare Output mode, phase correct and phase and frequency correct PWM.
COMnA1/COMnB/
COMnC1
COMnA0/COMnB0/
COMnC0 Description
00
Normal port operation, OCnA/OCnB/OCnC
disconnected.
01
WGM13:0 = 8, 9 10 or 11: Toggle OC1A on
Compare Match, OC1B and OC1C
disconnected (normal port operation). For all
other WGM1 settings, normal port operation,
OC1A/OC1B/OC1C disconnected.
10
Clear OCnA/OCnB/OCnC on compare
match when up-counting. Set
OCnA/OCnB/OCnC on compare match
when counting down.
11
Set OCnA/OCnB/OCnC on compare match
when up-counting. Clear
OCnA/OCnB/OCnC on compare match
when counting down.
Table 15-4. Waveform Generation mode bit description
(1)
.
Mode WGMn3
WGMn2
(CTCn)
WGMn1
(PWMn1)
WGMn0
(PWMn0)
Timer/Counter mode of
operation TOP
Update of
OCRnx at
TOVn flag
set on
0 0 0 0 0 Normal 0xFFFF Immediate MAX
1 0 0 0 1 PWM, phase correct, 8-bit 0x00FF TOP BOTTOM
2 0 0 1 0 PWM, phase correct, 9-bit 0x01FF TOP BOTTOM
3 0 0 1 1 PWM, phase correct, 10-bit 0x03FF TOP BOTTOM
4 0 1 0 0 CTC OCRnA Immediate MAX
5 0 1 0 1 Fast PWM, 8-bit 0x00FF TOP TOP
6 0 1 1 0 Fast PWM, 9-bit 0x01FF TOP TOP
7 0 1 1 1 Fast PWM, 10-bit 0x03FF TOP TOP
81000
PWM, phase and frequency
Correct
ICRn BOTTOM BOTTOM
91001
PWM, phase and frequency
Correct
OCRnA BOTTOM BOTTOM
10 1 0 1 0 PWM, phase correct ICRn TOP BOTTOM