![](http://datasheet.mmic.net.cn/30000/MR80C32-20-D_datasheet_2377239/MR80C32-20-D_133.png)
133
8154B–AVR–07/09
ATmega16A
17.11.2
TCNT2 – Timer/Counter Register
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.
17.11.3
OCR2 – Output Compare Register
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.
17.11.4
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 Oscil-
lator 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 hard-
ware. 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 hard-
ware. 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 hard-
ware. 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.
Bit
765
4321
0
TCNT2[7:0]
TCNT2
Read/Write
R/W
Initial Value
000
0000
0
Bit
765
432
10
OCR2[7:0]
OCR2
Read/Write
R/W
Initial Value
0
Bit
765
4
3
2
1
0
–
AS2
TCN2UB
OCR2UB
TCR2UB
ASSR
Read/Write
R
R/W
R
Initial Value
0