Table 51. Waveform Generation Mode Bit Description (Continued)
Timer/Count
er Mode of
Update of
OCRx at
TOV Flag
Mode WGM02 WGM01 WGM00 Operation
TOP
–
Set on(1)(2)
4
5
1
1
0
0
0
1
Reserved
–
–
PWM, Phase
Correct
OCRA
TOP
BOTTOM
6
7
1
1
1
1
0
1
Reserved
Fast PWM
–
–
–
OCRA
TOP
TOP
Notes: 1. MAX
= 0xFF
2. BOTTOM = 0x00
Timer/Counter Control
Register B – TCCR0B
Bit
7
FOC0A
W
6
FOC0B
W
5
–
4
–
3
2
CS02
R
1
CS01
R/W
0
0
WGM02
CS00
R/W
0
TCCR0B
Read/Write
Initial Value
R
0
R
0
R
0
0
0
0
• Bit 7 – FOC0A: Force Output Compare A
The FOC0A bit is only active when the WGM bits specify a non-PWM mode.
However, for ensuring compatibility with future devices, this bit must be set to zero when
TCCR0B is written when operating in PWM mode. When writing a logical one to the
FOC0A bit, an immediate Compare Match is forced on the Waveform Generation unit.
The OC0A output is changed according to its COM0A1:0 bits setting. Note that the
FOC0A bit is implemented as a strobe. Therefore it is the value present in the
COM0A1:0 bits that determines the effect of the forced compare.
A FOC0A strobe will not generate any interrupt, nor will it clear the timer in CTC mode
using OCR0A as TOP.
The FOC0A bit is always read as zero.
• Bit 6 – FOC0B: Force Output Compare B
The FOC0B bit is only active when the WGM bits specify a non-PWM mode.
However, for ensuring compatibility with future devices, this bit must be set to zero when
TCCR0B is written when operating in PWM mode. When writing a logical one to the
FOC0B bit, an immediate Compare Match is forced on the Waveform Generation unit.
The OC0B output is changed according to its COM0B1:0 bits setting. Note that the
FOC0B bit is implemented as a strobe. Therefore it is the value present in the
COM0B1:0 bits that determines the effect of the forced compare.
A FOC0B strobe will not generate any interrupt, nor will it clear the timer in CTC mode
using OCR0B as TOP.
The FOC0B bit is always read as zero.
• Bits 5:4 – Res: Reserved Bits
These bits are reserved bits in the ATmega48/88/168 and will always read as zero.
• Bit 3 – WGM02: Waveform Generation Mode
See the description in the “Timer/Counter Control Register A – TCCR0A” on page 95.
98
ATmega48/88/168
2545D–AVR–07/04
ATMEL [ ATMEL ]
