Datasheet
159
7593L–AVR–09/12
AT90USB64/128
Notes: 1. MAX= 0xFF
2. BOTTOM= 0x00
16.8.2 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 – Res: Reserved bits
These bits are reserved bits in the AT90USB64/128 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 156.
5 1 0 1 PWM, phase correct OCRA TOP BOTTOM
6110Reserved – – –
7111Fast PWM OCRATOP TOP
Table 16-7. Waveform Generation mode bit description. (Continued)
Mode WGM2 WGM1 WGM0
Timer/Counter
mode of operation TOP
Update of
OCRx at
TOV flag
set on
(1)(2)
Bit 76543210
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