109
8025I–AVR–02/09
ATmega48P/88P/168P/328P
12.9.2
TCCR0B – Timer/Counter Control Register B
• 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 ATmega48P/88P/168P/328P and will always read as zero.
• Bit 3 – WGM02: Waveform Generation Mode
See the description in the
”TCCR0A – Timer/Counter Control Register A” on page 106
.
• Bits 2:0 – CS02:0: Clock Select
The three Clock Select bits select the clock source to be used by the Timer/Counter.
Bit
7
6
5
4
3
2
1
0
FOC0A
FOC0B
–
–
WGM02
CS02
CS01
CS00
TCCR0B
Read/Write
W
W
R
R
R/W
R/W
R/W
R/W
Initial Value
0
0
0
0
0
0
0
0