
86
8008H–AVR–04/11
ATtiny48/88
Notes:
1. MAX
= 0xFF
Bits 2:0 – CS0[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/Counter0, transitions on the T0 pin will clock the
counter even if the pin is configured as an output. This feature allows software control of the
counting.
11.8.2
TCNT0 – Timer/Counter Register
The Timer/Counter Register gives direct access, both for read and write operations, to the
Timer/Counter unit 8-bit counter. Writing to the TCNT0 Register blocks (removes) the Compare
Match on the following timer clock. Modifying the counter (TCNT0) while the counter is running,
introduces a risk of missing a Compare Match between TCNT0 and the OCR0x Registers.
11.8.3
OCR0A – Output Compare Register A
The Output Compare Register A contains an 8-bit value that is continuously compared with the
counter value (TCNT0). A match can be used to generate an Output Compare interrupt.
Table 11-2.
CTC Mode Bit Description
Mode
CTC0
Timer/Counter
Mode of Operation
TOP
Update of
OCRx at
TOV Flag
0
Normal
0xFF
Immediate
MAX
1
CTC
OCRA
Immediate
MAX
Table 11-3.
Clock Select Bit Description
CS02
CS01
CS00
Description
0
No clock source (Timer/Counter stopped)
00
1
clkI/O (No prescaling)
01
0
clkI/O/8 (From prescaler)
01
1
clkI/O/64 (From prescaler)
10
0
clkI/O/256 (From prescaler)
10
1
clkI/O/1024 (From prescaler)
1
0
External clock source on T0 pin. Clock on falling edge.
1
External clock source on T0 pin. Clock on rising edge.
Bit
7
654
32
10
TCNT0[7:0]
TCNT0
Read/Write
R/W
Initial Value
0
Bit
7
654
32
10
OCR0A[7:0]
OCR0A
Read/Write
R/W
Initial Value
0