Rainbow Electronics ATtiny43U - Manual (Page 93)

93
8048B–AVR–03/09
Note: 1. MAX = 0xFF, BOTTOM = 0x00
12.9.3 TCCR0B – Timer/Counter Control Register B
12.9.4 TCCR1B – Timer/Counter Control Register B
• Bit 7 – FOCnA: Force Output Compare A
The FOCnA 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
TCCRnB is written when operating in PWM mode. When writing a logical one to the FOCnA bit,
an immediate Compare Match is forced on the Waveform Generation unit. The OCnA output is
changed according to its COMnA1:0 bits setting. Note that the FOCnA bit is implemented as a
strobe. Therefore it is the value present in the COMnA1:0 bits that determines the effect of the
forced compare.
A FOCnA strobe will not generate any interrupt, nor will it clear the timer in CTC mode using
OCRnA as TOP.
The FOCnA bit is always read as zero.
• Bit 6 – FOCnB: Force Output Compare B
The FOCnB bit is only active when the WGM bits specify a non-PWM mode.
Table 12-8. Waveform Generation Mode Bit Description
Mode WGMn2 WGMn1 WGMn0
Timer/Counter
Mode of
Operation
TOP
Update of
OCRx at
TOV Flag
Set on
(1)
0 0 0 0 Normal 0xFF Immediate MAX
1 0 0 1
PWM, Phase
Correct
0xFF TOP BOTTOM
2 0 1 0 CTC OCRnA Immediate MAX
3 0 1 1 Fast PWM 0xFF TOP MAX
4 1 0 0 Reserved – – –
5 1 0 1
PWM, Phase
Correct
OCRnA TOP BOTTOM
6 1 1 0 Reserved – – –
7 1 1 1 Fast PWM OCRnA TOP TOP
Bit 7 6 5 4 3 2 1 0
0x33 (0x53) 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
Bit 7 6 5 4 3 2 1 0
0x2E (0x4E) FOC1A FOC1B – – WGM12 CS12 CS11 CS10 TCCR1B
Read/Write W W R R R/W R/W R/W R/W
Initial Value 0 0 0 0 0 0 0 0