Attiny2313 – Rainbow Electronics ATtiny2313 User Manual
Page 77
77
ATtiny2313
2543A–AVR–08/03
Table 40 shows the COM0B1:0 bit functionality when the WGM02:0 bits are set to
phase correct PWM mode.
Note:
1. A special case occurs when OCR0B equals TOP and COM0B1 is set. In this case,
the Compare Match is ignored, but the set or clear is done at TOP. See “Phase Cor-
rect PWM Mode” on page 72 for more details.
• Bits 3, 2 – Res: Reserved Bits
These bits are reserved bits in the ATtiny2313 and will always read as zero.
• Bits 1:0 – WGM01:0: Waveform Generation Mode
Combined with the WGM02 bit found in the TCCR0B Register, these bits control the
counting sequence of the counter, the source for maximum (TOP) counter value, and
what type of waveform generation to be used, see Table 41. Modes of operation sup-
ported 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 95).
Notes:
1. MAX = 0xFF
2. BOTTOM = 0x00
Table 40. Compare Output Mode, Phase Correct PWM Mode
(1)
COM0B1
COM0B0
Description
0
0
Normal port operation, OC0B disconnected.
0
1
Reserved
1
0
Clear OC0B on Compare Match when up-counting. Set OC0B on
Compare Match when down-counting.
1
1
Set OC0B on Compare Match when up-counting. Clear OC0B on
Compare Match when down-counting.
Table 41. Waveform Generation Mode Bit Description
Mode
WGM2
WGM1
WGM0
Timer/Counter
Mode of
Operation
TOP
Update of
OCRx at
TOV Flag
Set on
(1)(2)
0
0
0
0
Normal
0xFF
Immediate
MAX
1
0
0
1
PWM, Phase
Correct
0xFF
TOP
BOTTOM
2
0
1
0
CTC
OCRA
Immediate
MAX
3
0
1
1
Fast PWM
0xFF
TOP
MAX
4
1
0
0
Reserved
–
–
–
5
1
0
1
PWM, Phase
Correct
OCRA
TOP
BOTTOM
6
1
1
0
Reserved
–
–
–
7
1
1
1
Fast PWM
OCRA
TOP
TOP