Rainbow Electronics ATtiny43U - Manual (Page 94)

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8048B–AVR–03/09
ATtiny43U
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 FOCnB bit,
an immediate Compare Match is forced on the Waveform Generation unit. The OCnB output is
changed according to its COMnB1:0 bits setting. Note that the FOCnB bit is implemented as a
strobe. Therefore it is the value present in the COMnB1:0 bits that determines the effect of the
forced compare.
A FOCnB strobe will not generate any interrupt, nor will it clear the timer in CTC mode using
OCRnB as TOP.
The FOCnB bit is always read as zero.
• Bits 5, 4 – Res: Reserved Bits
These bits are reserved and will always read zero.
• Bit 3 – WGMn2: Waveform Generation Mode
See the description in the “Register Description” on page 90 .
• Bits 2:0 – CSn[2:0]: Clock Select
The three Clock Select bits select the clock source to be used by the Timer/Counter.
If external pin modes are used for the Timer/Countern, transitions on the Tn pin will clock the
counter even if the pin is configured as an output. This feature allows software control of the
counting.
12.9.5 TCNT0 – Timer/Counter Register
Table 12-9. Clock Select Bit Description
CSn2 CSn1 CSn0 Description
0 0 0 No clock source (Timer/Counter stopped)
0 0 1 clk
I/O
/(No prescaling)
0 1 0 clk
I/O
/8 (From prescaler)
0 1 1 clk
I/O
/64 (From prescaler)
1 0 0 clk
I/O
/256 (From prescaler)
1 0 1 clk
I/O
/1024 (From prescaler)
1 1 0 External clock source on Tn pin. Clock on falling edge.
1 1 1 External clock source on Tn pin. Clock on rising edge.
Bit 7 6 5 4 3 2 1 0
0x32 (0x52) TCNT0[7:0] TCNT0
Read/Write R/W R/W R/W R/W R/W R/W R/W R/W
Initial Value 0 0 0 0 0 0 0 0