Atmel ATmega128 User Manual

159
2467S–AVR–07/09
ATmega128
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.
• Bit 6 – TOIE2: Timer/Counter2 Overflow Interrupt Enable
When the TOIE2 bit is written to one, and the I-bit in the Status Register is set (one), the
Timer/Counter2 Overflow interrupt is enabled. The corresponding interrupt is executed if an
overflow in Timer/Counter2 occurs, i.e., when the TOV2 bit is set in the Timer/Counter Interrupt
Flag Register – TIFR.
101clk
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
Table 68. Clock Select Bit Description
CS22 CS21 CS20 Description
Bit 76543210
TCNT2[7:0] TCNT2
Read/Write R/W R/W R/W R/W R/W R/W R/W R/W
Initial Value00000000
Bit 76543210
OCR2[7:0] OCR2
Read/Write R/W R/W R/W R/W R/W R/W R/W R/W
Initial Value00000000
Bit 7654 3210
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

Atmel ATmega128 Specifications

General

Brand	Atmel
Model	ATmega128
Category	Microcontrollers
Language	English