Datasheet

ATmega164A/PA/324A/PA/644A/PA/1284/P
 2018 Microchip Technology Inc. Data Sheet Complete DS40002070A-page 163
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 OCR2x Registers.
17.11.4 OCR2A – Output Compare Register A
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.
17.11.5 OCR2B – Output Compare Register B
The Output Compare Register B 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 OC2B pin.
17.11.6 ASSR – Asynchronous Status Register
• Bit 6 – EXCLK: Enable External Clock Input
When EXCLK is written to one, and asynchronous clock is selected, the external clock input buffer is enabled
and an external clock can be input on Timer Oscillator 1 (TOSC1) pin instead of a 32kHz crystal. Writing to
EXCLK should be done before asynchronous operation is selected. Note that the crystal Oscillator will only run
when this bit is zero.
• Bit 5 – AS2: Asynchronous Timer/Counter2
When AS2 is written to zero, Timer/Counter2 is clocked from the I/O clock, clk
I/O
. When AS2 is written to one,
Timer/Counter2 is clocked from a crystal Oscillator connected to the Timer Oscillator 1 (TOSC1) pin. When the
value of AS2 is changed, the contents of TCNT2, OCR2A, OCR2B, TCCR2A and TCCR2B might be corrupted.
• Bit 4 – TCN2UB: Timer/Counter2 Update Busy
When Timer/Counter2 operates asynchronously and TCNT2 is written, this bit becomes set. When TCNT2 has
been updated from the temporary storage register, this bit is cleared by hardware. A logical zero in this bit
indicates that TCNT2 is ready to be updated with a new value.
• Bit 3 – OCR2AUB: Output Compare Register2 Update Busy
When Timer/Counter2 operates asynchronously and OCR2A is written, this bit becomes set. When OCR2A has
been updated from the temporary storage register, this bit is cleared by hardware. A logical zero in this bit
indicates that OCR2A is ready to be updated with a new value.
Bit 76543210
(0xB3) OCR2A[7:0] OCR2A
Read/Write R/W R/W R/W R/W R/W R/W R/W R/W
Initial Value00000000
Bit 76543210
(0xB4) OCR2B[7:0] OCR2B
Read/Write R/W R/W R/W R/W R/W R/W R/W R/W
Initial Value00000000
Bit 7 6 5 4 3 2 1 0
(0xB6)
– EXCLK AS2 TCN2UB OCR2AUB OCR2BUB TCR2AUB TCR2BUB ASSR
Read/Write R R/W R/W R R R R R
Initial Value 0 0 0 0 0 0 0 0