attiny13-20ss ATMEL Corporation, attiny13-20ss Datasheet - Page 72

• Manufacturer Part Number: attiny13-20ss
• Description: 8-bit Microcontroller With 1k Bytes In-system Programmable Flash - Atmel Corporation
• Manufacturer: ATMEL Corporation

Timer/Counter Control
Register B – TCCR0B
72
ATtiny13
• 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 ATtiny13 and will always read as zero.
• Bit 3 – WGM02: Waveform Generation Mode
See the description in the “Timer/Counter Control Register A – TCCR0A” on page 69.
• Bits 2:0 – CS02:0: Clock Select
The three Clock Select bits select the clock source to be used by the Timer/Counter.
Table 33. Clock Select Bit Description
Bit
Read/Write
Initial Value
CS02
0
0
0
0
1
CS01
0
0
1
1
0
FOC0A
W
7
0
CS00
0
1
0
1
0
FOC0B
W
6
0
Description
No clock source (Timer/Counter stopped)
clk
clk
clk
clk
I/O
I/O
I/O
I/O
/(No prescaling)
/8 (From prescaler)
/64 (From prescaler)
/256 (From prescaler)
R
5
–
0
4
R
0
–
WGM02
R/W
3
0
CS02
R/W
2
0
CS01
R/W
1
0
CS00
R/W
2535G–AVR–01/07
0
0
TCCR0B