Timer/counter register – tcnt2, Output compare register a – ocr2a, Atmega169v/l – Rainbow Electronics Atmega169L User Manual
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136
ATmega169V/L
2514A–AVR–08/02
• Bit 2:0 – CS22:0: Clock Select
The three Clock Select bits select the clock source to be used by the Timer/Counter, see
Table 65.
Timer/Counter Register –
TCNT2
The Timer/Counter Register gives direct access, both for read and write operations, to
the Timer/Counter unit 8-bit counter. Writing to the TCNT2 Register blocks (removes)
the compare match on the following timer clock. Modifying the counter (TCNT2) while
the counter is running, introduces a risk of missing a compare match between TCNT2
and the OCR2A Register.
Output Compare Register A –
OCR2A
The Output Compare Register A contains an 8-bit value that is continuously compared
with the counter value (TCNT2). A match can be used to generate an Output Compare
interrupt, or to generate a waveform output on the OC2A pin.
Table 65. Clock Select Bit Description
CS22
CS21
CS20
Description
0
0
0
No clock source (Timer/Counter stopped).
0
0
1
clk
T2S
/(No prescaling)
0
1
0
clk
T2S
/8 (From prescaler)
0
1
1
clk
T2S
/32 (From prescaler)
1
0
0
clk
T2S
/64 (From prescaler)
1
0
1
clk
T2S
/128 (From prescaler)
1
1
0
clk
T
2
S
/256 (From prescaler)
1
1
1
clk
T
2
S
/1024 (From prescaler)
Bit
7
6
5
4
3
2
1
0
TCNT2[7:0]
TCNT2
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
Bit
7
6
5
4
3
2
1
0
OCR2A[7:0]
OCR2A
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