Datasheet

126
ATmega32A [DATASHEET]
Atmel-8155D-AVR-ATmega32A-Datasheet_02/2014
18.11.4 ‘ASSR – Asynchronous Status Register
• Bit 3 – AS2: Asynchronous Timer/Counter2
When AS2 is written to zero, Timer/Counter 2 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, OCR2, and TCCR2 might be corrupted.
• Bit 2 – 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 1 – OCR2UB: Output Compare Register2 Update Busy
When Timer/Counter2 operates asynchronously and OCR2 is written, this bit becomes set. When OCR2 has been
updated from the temporary storage register, this bit is cleared by hardware. A logical zero in this bit indicates that
OCR2 is ready to be updated with a new value.
• Bit 0 – TCR2UB: Timer/Counter Control Register2 Update Busy
When Timer/Counter2 operates asynchronously and TCCR2 is written, this bit becomes set. When TCCR2 has
been updated from the temporary storage register, this bit is cleared by hardware. A logical zero in this bit indicates
that TCCR2 is ready to be updated with a new value.
If a write is performed to any of the three Timer/Counter2 Registers while its update busy flag is set, the updated
value might get corrupted and cause an unintentional interrupt to occur.
The mechanisms for reading TCNT2, OCR2, and TCCR2 are different. When reading TCNT2, the actual timer
value is read. When reading OCR2 or TCCR2, the value in the temporary storage register is read.
18.11.5 TIMSK – Timer/Counter Interrupt Mask Register
• 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,
that is, 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, that is, when
the TOV2 bit is set in the Timer/Counter Interrupt Flag Register – TIFR.
Bit 76543 2 1 0
– – – – AS2 TCN2UB OCR2UB TCR2UB ASSR
Read/Write R R R R R/W R R R
Initial Value00000 0 0 0
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