Timer/counter register – tcnt2, Output compare register – ocr2, Timer/counter interrupt mask register – timsk – Rainbow Electronics ATmega128L User Manual
Page 153: Atmega128(l)
153
ATmega128(L)
2467B–09/01
If external pin modes are used for the Timer/Counter2, transitions on the T2 pin will
clock the counter even if the pin is configured as an output. This feature allows software
control of the counting.
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 OCR2 register.
Output Compare Register –
OCR2
The Output Compare Register 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 OC2 pin.
Timer/Counter Interrupt Mask
Register – TIMSK
• Bit 7- OCIE2: Timer/Counter2 Output Compare Match Interrupt Enable
When the OCIE2 bit is written to one, and the I-bit in the Status Register is set (one), the
Timer/Counter2 Compare Match interrupt is enabled. The corresponding interrupt is
executed if a compare match in Timer/Counter2 occurs, i.e. when the OCF2 bit is set in
the Timer/Counter Interrupt Flag Register – TIFR.
Table 68. Clock Select Bit Description
CS22
CS21
CS20
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
/32 (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 T2 pin. Clock on falling edge
1
1
1
External clock source on T2 pin. Clock on rising edge
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
OCR2[7:0]
OCR2
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
OCIE2
TOIE2
TICIE1
OCIE1A
OCIE1B
TOIE1
OCIE0
TOIE0
TIMSK
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