Data Sheet

157
ATmega48A/PA/88A/PA/168A/PA/328/P [DATASHEET]
Atmel-8271H-AVR- ATmega-Datasheet_08/2014
18.11.2 TCCR2B – Timer/Counter Control Register B
• Bit 7 – FOC2A: Force Output Compare A
The FOC2A 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 TCCR2B is written
when operating in PWM mode. When writing a logical one to the FOC2A bit, an immediate Compare Match is
forced on the Waveform Generation unit. The OC2A output is changed according to its COM2A1:0 bits setting.
Note that the FOC2A bit is implemented as a strobe. Therefore it is the value present in the COM2A1:0 bits that
determines the effect of the forced compare.
A FOC2A strobe will not generate any interrupt, nor will it clear the timer in CTC mode using OCR2A as TOP.
The FOC2A bit is always read as zero.
• Bit 6 – FOC2B: Force Output Compare B
The FOC2B 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 TCCR2B is written
when operating in PWM mode. When writing a logical one to the FOC2B bit, an immediate Compare Match is
forced on the Waveform Generation unit. The OC2B output is changed according to its COM2B1:0 bits setting.
Note that the FOC2B bit is implemented as a strobe. Therefore it is the value present in the COM2B1:0 bits that
determines the effect of the forced compare.
A FOC2B strobe will not generate any interrupt, nor will it clear the timer in CTC mode using OCR2B as TOP.
The FOC2B bit is always read as zero.
• Bits 5:4 – Reserved
These bits are reserved bits in the ATmega48A/PA/88A/PA/168A/PA/328/P and will always read as zero.
• Bit 3 – WGM22: Waveform Generation Mode
See the description in the ”TCCR2A – Timer/Counter Control Register A” on page 154.
• Bit 2:0 – CS22:0: Clock Select
The three Clock Select bits select the clock source to be used by the Timer/Counter, see Table 18-9 on page
157.
Bit 7 6 5 4 3 2 1 0
(0xB1)
FOC2A FOC2B – – WGM22 CS22 CS21 CS20 TCCR2B
Read/Write W W R R R/W R/W R/W R/W
Initial Value 0 0 0 0 0 0 0 0
Table 18-9. Clock Select Bit Description
CS22 CS21 CS20 Description
0 0 0 No clock source (Timer/Counter stopped).
001clk
T2S
/(No prescaling)
010clk
T2S
/8 (From prescaler)
011clk
T2S
/32 (From prescaler)
100clk
T2S
/64 (From prescaler)