Rainbow Electronics ATtiny43U - Manual (Page 92)

92
8048B–AVR–03/09
ATtiny43U
Table 12-6 on page 92 shows the COMnB[1:0] bit functionality when the WGMn[2:0] bits are set
to fast PWM mode.
Note: 1. A special case occurs when OCRnB equals TOP and COMnB1 is set. In this case, the Com-
pare Match is ignored, but the set or clear is done at TOP. See “Fast PWM Mode” on page 85
for more details.
Table 12-7 shows the COMnB[1:0] bit functionality when the WGMn2:0 bits are set to phase cor-
rect PWM mode.
Note: 1. A special case occurs when OCRnB equals TOP and COMnB1 is set. In this case, the Com-
pare Match is ignored, but the set or clear is done at TOP. See “Phase Correct PWM Mode” on
page 87 for more details.
• Bits 3, 2 – Res: Reserved Bits
These bits are reserved and will always read zero.
• Bits 1:0 – WGMn[1:0]: Waveform Generation Mode
Combined with the WGMn2 bit 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 12-8 on page 93 . Modes of operation supported by the
Timer/Counter unit are: Normal mode (counter), Clear Timer on Compare Match (CTC) mode,
and two types of Pulse Width Modulation (PWM) modes (see
“Modes of Operation” on page 84 ).
Table 12-6. Compare Output Mode, Fast PWM Mode (1)
COMnB1 COMnB0 Description
0 0 Normal port operation, OCnB disconnected.
0 1 Reserved
1 0 Clear OCnB on Compare Match, set OC0B at TOP
1 1 Set OCnB on Compare Match, clear OC0B at TOP
Table 12-7. Compare Output Mode, Phase Correct PWM Mode (1)
COMnB1 COMnB0 Description
0 0 Normal port operation, OCnB disconnected.
0 1 Reserved
1 0
Clear OCnB on Compare Match when up-counting. Set OCnB on
Compare Match when down-counting.
1 1
Set OCnB on Compare Match when up-counting. Clear OCnB on
Compare Match when down-counting.