AT90S/LS4434 and AT90S/LS8535
42
The Stop condition provides a Timer Enable/Disable function. The prescaled CK modes are scaled directly from the CK
oscillator clock.
Timer/Counter2 – TCNT2
This 8-bit register contains the value of Timer/Counter2.
Timer/Counter2 is realized as an up or up/down (in PWM mode) counter with read and write access. If the Timer/Counter2
is written to and a clock source is selected, it continues counting in the timer clock cycle following the write operation.
Timer/Counter2 Output Compare Register – OCR2
The Output Compare Register is an 8-bit read/write register.
The Timer/Counter Output Compare Register contains the data to be continuously compared with Timer/Counter2. Actions
on compare matches are specified in TCCR2. A compare match only occurs if Timer/Counter2 counts to the OCR2 value.
A software write that sets TCNT2 and OCR2 to the same value does not generate a compare match.
A compare match will set the compare interrupt flag in the CPU clock cycle following the compare event.
Timer/Counter2 in PWM Mode
When the PWM mode is selected, Timer/Counter2 and the Output Compare Register (OCR2) form an 8-bit, free-running,
glitch-free and phase correct PWM with outputs on the PD7(OC2) pin. Timer/Counter2 acts as an up/down counter, count-
ing up from $00 to $FF, where it turns and counts down again to zero before the cycle is repeated. When the counter value
matches the contents of the Output Compare Register, the PD7(OC2) pin is set or cleared according to the settings of the
COM21/COM20 bits in the Timer/Counter2 Control Register (TCCR2). Refer to Table 20 for details.
Table 19.
Timer/Counter2 Prescale Select
CS22
CS21
CS20
Description
0
0
0
Timer/Counter2 is stopped.
0
0
1
PCK2
0
1
0
PCK2/ 8
0
1
1
PCK2/ 32
1
0
0
PCK2/ 64
1
0
1
PCK2/128
1
1
0
PCK2/256
1
1
1
PCK2/1024
Bit
7
6
5
4
3
2
1
0
$24 ($44)
MSB
LSB
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
$23 ($43)
MSB
LSB
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